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Overview of Energetics and Homeostasis in Animals

Bioenergetics

Energy is often defined as capacity to do work, but in living systems it is best defined as ability to cause specific change. The different kinds of changes made by cells and living things or the use of energy by cells are 1.Changes in chemical bonds(chemical work) as in biosynthesis of new molecules for growth of new cells which requires new synthesis of molecules and maintenance of existing cells where large molecules easy to damage and must be recycled as in the formation of proteins, fats and other organic compounds. In synthesis of large molecules much energy is required. Cells need to change with time as it needs certain proteins during interphase as well as foods changes to be used by the body

2. Changes in location (mechanical work) Living things and cells undergo movement, to move relative to something else (e.g. flagellated cells sperm); move relative to environment like ciliated epithelium in bronchial tubes move particles relative to cells; muscle cells contract in one.

3. Changes in concentration across membrane (concentration work) as in when molecules or ions move against chemical

Notes in Animal Physiology by CCDivina………… 1

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concentration gradient (eg: cells must pump amino acids into cell)

4. Changes in cell's electrical potential (electrical work) as energy in electrochemicial gradient can be used to make ATP in bacteria, chloroplasts & mitochondria and ATP can be used to make electrochemical gradient (membrane potential) as in electric eel

5. Changes in thermal energy (heat). In homeotherms like the birds and mammals, relatively constant temperature must be maintained and heat production is the major use of food energy

6. Changes in bioluminescence ("light" work) such as in fireflies, some bacteria

The environmental energy available at earth's surface is largely light light energy. Many organisms capture light energy most plants, some bacteria, some protests are photosynthetic organisms called "phototrophs" Phototrophs are organisms which use light energy to make all molecules required for life from inorganic precursors like CO2 and H2O. Chemotrophs use chemical energy stored in light (eg: starch) as energy source during darkness; organisms get energy from source other than light. All animals, fungi, many protists, most bacteria and a few parasitic plants are chemotrophs. Energy is released from chemicals they take up from the


environment in fermentation, glycolysis, respiration and others sources too

Metabolic Rate is the energy used by organisms per unit time. It is measured in calories – amount of heat energy --> raise 1g H2O 1oC [14.5o to 15.5o C], linked to Krebs Cycle - MR is determined by O2 consumption often as VO2max where the minimal calories required for basic functions of life and the maximal calories is on the peak of metabolic activity as in cases of athletes in the Olympics . Metabolic Rates is greatly influenced by several variables such as age, sex, body size, temp, food levels, time of day, size of organism, hormonal balance, available O2

The basal metabolic rate (BMR) in endotherms (animals that derive body heat from own metabolism) is when they at rest without stress. In human males 1,600 - 1,800 Kc/d and females is 1,300 - 1,500 Kc/d.

HOMEOSTASIS is how Animals regulate their internal environment and maintain a steady state internal environment (constancy) in face of a changing external environment.

Animals adjust to these changes. Each stimuli the animal receives calls for corresponding response. Physiological Compensation is the short term


physiological adjustments or adaptations to environmental changes, i.e., homeostatic compensation Internal "Milieu" as Claude Bernard in 1880's referred to it is the internal environment of the interstitial fluids filling spaces between cells exchanging nutrients with the blood. The Constancy of Human milieu is body temperature of 37o C + 1o C; pH of 7.4 + 0.1 and blood sugar of 0.1% [mg% - 100 mg/100ml blood]

Homeostatic Regulation is the mechanisms that cells have evolved to maintain constancy.

A Homeostatic Regulator mechanism has 3 parts: receptor detects a change, controller processes the informa-tion and the effector produces the response.


Here are some examples of Homeostatic Regulation

1. Temperature : the hypothalmus regulates body temperature via homeostatic thermoregulation...

2. pH regulation of the blood . If the pH 7.4 + 0.1 has a shift of 0.4 pH unit , it will mean death. For example a crying baby blows off CO2 and lowers blood acidity (alkalosis) and person with bleeding stomach ulcers favors acidosis. Carbonic anhydrase converts CO2 + Notes in Animal Physiology by CCDivina………… 5

H2O <---> H2CO3 <---> H+ + HCO3

- . Hemoglobin of the red blood cells pick up H+ ions and buffering blood. Buffer is: a substance, as Hemoglobin and other proteins that in solution tends to stabilize the hydrogen-ion concentration by neutralizing, within limits, both acids and bases. If pH blood drops [H+ ^] then HCO3

- + H+ shifts ---> to H2CO3

and vice versa.

Calcium homeostasis.

In blood, the normal range is 9 to 11 mg%. Ca+2 is needed for nerve function, muscle contraction, blood clotting, etc.. Calcium regulation functions via antagonistic hormones . The thyroid makes calcitonin hormone that lowers Ca levels and causes Ca to be


deposited into bone reduces intestinal absorption of Ca and reduces Ca uptake by kidney. The parathyroid --> parathyroid hormone raises Ca levels, stimulates release Ca from bone and increases Ca uptake by intestine & kidney

4. Blood Glucose balance . the normal range of blood sugar is 80-120mg/100ml. The pancreas makes insulin and glucagon, which are antagonistic hormones

5. Osmoregulation maintains the water balance of organism. Osmosis is the net movement of water through a semi-permeable membrane like the cell


membrane. Terrestrial animals gain water from food & drink and lose water by urinating, defecating, & evaporation. Aquatic animals could be osmoconformer (when the internal [solute] same as environment) or osmoregulator when internal [solute] maintain constant level.

Osmoregulation is a challenge to both fresh water fish and seawater fish . Freshwater fish has greater internal solutes thus constantly gains water thru its body surface, its gills, and food it eats. To compensates it does not drink water and excretes large amounts dilute urine and regains most ions that are lost [Na, Cl, K] via food & gills.

altwater fish has less internal solutes, thus constantly loses water. It compensates by drinking saltwater, has urine that is very concentrated. It pumps ions [Na, Cl, K] out via gills


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Digestive System

Diets and feeding mechanisms vary extensively among animals.

All animals are heterotrophs and must obtain their nutrients by consuming organic molecules.

Animals may obtain nutrient by suspension, substrate deposit, and fluid or bulk feeding

Ingestion, digestion, absorption and elimination are the four main

stages of food processing.

Food processing in animals involves ingestion, digestion (enzymatic breakdown of the macromolecules of food into their monomers) absorption (the uptake of nutrient by body cells) and elimination (the passage of undigested materials out the body in feces.

An adequate diet provides fuel, carbon skeletons for biosynthesis and essential nutrients. Carbohydrates and fats are most often used as fuel. Monomer of carbohydrates, proteins, fats and nucleic acids are used in biosynthesis.

Animals store excess calories as glycogen in the liver and muscles and as fat in adipose tissue. Undernourished animals have diet deficient calories.


Essential nutrients must be supplied in pre-assembled form because of the blood lacks the machinery for biosynthesis; malnourished animals are missing one or more of the essential nutrients. Essential amino acids are those an animal cannot make from nitrogen-containing precursor. Animals can synthesis most essential fatty acid. There are a few essential unsaturated fatty acids.

Vitamins are organic molecules, many of which serve as coenzymes or parts of coenzymes; they are required in small amount.

Vitamins, their functions, deficiency symptoms and primary sourcesVITAMINS FUNCTION DEFICIENCY

SYMPTOMSPRIMARY SOURCES

Water Soluble VitaminsB1 THIAMINE

Formation of co-enzyme in Kreb’s cycle

Beriberi, neuritis, heart failure

Organ meats, grains

B2 RIBOFLAVIN

Co-factor in cellular respiration

Photophobia, skin fissures

Milk eggs. Liver, whole grains

B6 PYRIDOXINE

Co-enzyme in amino and fatty acid metabolism

Dermatitis and nervous disorders

Whole grains

B12 CYANOCOBALAMIN

Nucleic acid synthesis, prevents pernicious anemia

Pernicious anemia, malformed red blood cells

Organ meats, synthesized by intestinal bacteria


BIOTIN Protein synthesis, CO2

fixation, amine metabolism

Scaly dermatitis, muscle pains, weakness

Egg white, synthesized by digestive flora

FOLIC ACID Nucleic acid synthesis. Red blood cells formation

Anemia, failure of red blood cells to mature

Meats

NIACIN Coenzyme in hydrogen transport

Pellagra, skin lesions, digestive disturbances

Whole grains

PANTHO-THENIC ACID

Forms part of coenzyme A

Neuromotor and cardiovascular disorders

Most foods

C ASCORBIC ACID

Vital to collagen and ground substances

Scurvy, failure to form connective tissues

Citrus fruits

FAT SOLUBLEA CAROTENE

Visual pigment formation, maintains epithelial structure.

Nigh blindness, skin lesions

Egg yolk, green and yellow vegetables

D CALCIFEROL

Increase calcium absorption from but, bone and tooth formation

Rickets, defective bone formation

Fish oils. Liver

E TOCOPHEROL

Maintains red blood cells

Increased fragility of red blood cells

Green leafy vegetables

Knaphthaquinone

Stimulates prothrombin synthesis by liver

Failure of blood-clotting mechanism

Synthesis by intestinal flora


Mineral salt are inorganic nutrients required by animals either as macronutrients or micronutrients. The essential macronutrients are potassium, sodium, chlorine, phosphorus, calcium, magnesium and sulfur. The micronutrients are iron, copper, zinc and manganese. Cobalt and iodine, valadium, selenium are required trace elements. The functions of the different minerals in the animal’s organism are presented below.MINERALS FUNCTION PRIMARY SOURCEESSENTIAL MINERALSCalcium Component of bone and

teeth, essential for normal blood clotting, needed for normal muscle, nerve and cell function

milk and other dairy products, green leafy vegetables

CHLORINE Principal negative ion in interstitial fluid, important in fluid balance and in acid-base balance

Most food, table salt

MAGNESIUM Component of many co-enzymes, balance between magnesium and calcium ions needed for normal muscle and never function

Many foods

PHOSPHORUS

As calcium phosphate, an important structural component of bone, essential for energy transfer and storage, (component of ATP) and form many other metabolic processes, component of DNA, RNA and many proteins

All foods

POTASSIUM Principal positive ion within cells, influence muscle contraction and nerve excitability

Many foods

SODIUM Principal positive ion in interstitial fluid, important in fluid balance, essential for conduction of

Most foods, table salt


nerve impulsesSULFUR Component of many protein,

essential for normal metabolic activity

Meat, fish, legumes, nuts

TRACE MINERALSCOBALT Component of vitamin

B12, essential for red blood cell production

Meat, dairy products

COPPER Component of many enzymes, essential for melanin and hemoglobin syntheses

Lever, eggs, fish, whole-wheat flour, beans

FLUORINE Component of bone and teeth

Some natural waters

IODINE Component of hormones that stimulate metabolic rate

Seafood, iodized salt, Vegetables grown in iodine-rich soils

IRON Component of hemoglobin, myoglobin, cytochrome and other enzymes essential to oxygen transport and cellular respiration

Meat specially liver, nuts, egg yolk, legumes

MANGANESE

Activates many enzymes, essential for urea formation

Whole grain cereal, egg yolk, green vegetables

ZINC Component of enzymes, peptidases important in wound healing and fertilization

Shellfish, meats, liver

Mammalian digestive system

The mammalian digestive tract has a four-layered wall over most of its Notes in Animal Physiology by CCDivina………… 14

length; the smooth muscle layer propels food along the tract by peristalsis and regulates its passage through strategic points by means of sphincters.

Mammals have accessory glands that add digestive secretions to the tract through ducts. These are the salivary glands, pancreas and liver.

Digestion begins in the oral cavity, whereas teeth -chew food into smaller particles that are exposed to salivary amylase. Saliva contains buffers, antibacterial agents and mucin for lubricating the food.

The esophagus conducts food from the pharynx other stomach by involuntary peristaltic waves.

The stomach stores food and secretes gastric juice which converts a mass to acid chyme, gastric juice include hydrochloric acids enzyme pepsin. Nerve impulse and other hormone gastrin regulate gastric motility and secretion.

Most digestion and virtually all absorption occur in the small intestine, the longest segment of the alimentary canal

The pancreas and gallbladder, which stores bile secreted by the liver, empty ducts into the duodenum the first part to the small intestine, Regulatory hormones such as secretin and cholecystokinin regulates the activities of the pancreas and gall bladder.

Digestive Tract and its Function


The primary function of the alimentary tract is to provide body with continual supply of water, electrolytes and nutrients. To do so, food must be moved along the alimentary tract at an appropriate rate for digestive and absorptive functions to take place.

The alimentary tract shows major anatomical differences between its parts. Each part is adapted for specific functions such as

1. simple passage of food from one point to another, as in esophagus

2. storage of food in the body of the stomach or fecal matter in the descending colon

3. digestion of food in the stomach, duodenum, jejunum and ileum

4. absorption of digestive end-products in the entire small intestines and proximal half of the colon

One of the most important features of gastrointestinal tract is the myriad of auto regulatory processes in the gut that keeps the food moving at an appropriate pace- slow enough for digestion and absorption to provide the nutrients needed by the body.

Characteristics of the Intestinal Wall

A typical section of the intestinal wall, showing layers from the outside to inward

1. the serosa2. a longitudinal muscle layer


3. a circular muscle layer4. the submucosa5. the mucosa

In addition, a sparse layer of smooth muscle fibers, the muscularis mucosa lies in the deeper layers of mucosa. The different layers of smooth muscles perform the motor functions of the gut.

Characteristic of Intestinal Smooth Muscle

1. The Functional Syncitium.The individual smooth muscle fiber

lies close to each other. About 12 percent of the membrane surfaces are actually fused with membranes of adjacent muscle fibers in the form of a nexus and most of the remainder of the cell membranes of adjacent fibers lie in extremely close opposite.

Measurements of ionic transport through these areas of close contact demonstrate extremely low electrical resistance, so much so that intracellular electrical current can travel very easily form one smooth muscle fiber to another. Therefore the smooth muscle of the gastrointestinal tract performs as a functional syncitium which means that action potentials originating in one smooth muscle fiber are generally propagated from fiber to fiber.


2 . Contraction of Intestinal Muscle

The Smooth muscles of the gastrointestinal tract exhibits both tonic and rhythmic contractions.

Tonic contraction is continuous lasting minute after minute or even hour after hour sometime increasing or decreasing in intensity but nevertheless continuing. It is caused by a series of action potential, the frequency of these determine the degree of tonic contraction. The intensity of tonic contraction in each set of the gut determines the steady pressure of the segment, the tonic contraction of the sphincters determines the amount of resistance offered at the sphincter to the movement of intestinal contents. In this way, the pyloric the ileocecal and the anal sphincters help to regulate food movement in the gut.

The rhythmic contraction of the gastrointestinal smooth muscles is responsible for the phasic function of the gut, such a mixing of the food and peristaltic propulsion of food.

Innervations of the Gut – Intramural Plexus

The intramural plexus is especially responsible for many neurogenic reflexes that occur locally in the gut, such as reflexes from the mucosal epithelium to


increase the activity of the gut muscle or to cause localize secretion of digestive juices by the submucosal glands. The plexus is also intimately involved in coordination of the motor movements of the gastrointestinal tract.

In higher forms of animals, nutrition is ingestion, digestion and assimilation and egestion. Ingestion is acquiring the food from the environment. Digestion is the physical and chemical breakdown of food to be assimilated or absorbed in circulation. Egestion is the release of the undigested food.

Digestion needs the activities of different digestive enzymes to break them down chemically into absorbable forms. In man, digestion takes place along the digestive or alimentary tract, the organs involved in digestion are the mouth, the pharynx, esophagus, stomach, small intestines and large intestines. The digestive accessory glands are the salivary gland, liver and pancreas.

Digestion takes place right after ingestion. In the mouth, the food is chewed or masticated into smaller particles to expose more surface area for the action of the enzymes. The teeth are of different kinds, like the incisors for biting, the canines for tearing, the molars for grinding and crushing. The tongue mixes the masticated food with the saliva secreted by the salivary gland.


Saliva contains water, mucin and ptyalin, an enzyme that breaks down carbohydrates into disaccharides. When food is thoroughly chewed it proceeds to the pharynx and esophagus by swallowing or deglutition. The food forms a bolus and moves along the tract through the wave-like contraction of muscles in the walls, this contraction is known as peristalsis.

The stomach is a large sac-like organ that is closed at its upper part by the cardiac sphincters and the lower part of they pyloric sphincter. The stomach stores the temporary partially digested food. The glands of the stomach wall produces gastric juice that contains hydrochloric acid (HCl) and pepsin.

Pepsin breaks down proteins into polypeptides. The food is in a semi-liquid chyme form when it leaves the stomach to proceed to the small intestines.

The small intestines are approximately 22 meters long and have three sections– the duodenum, jejunum and ileum. Final digestion and absorption takes place in this stretch of organ. Secretory gland cells of the intestinal walls and the pancreas secrete enzymes that finally breaks down disaccharides into monosaccharides, lipids into fatty acids and glycerol, polypeptides into amino acids and nucleic acids into nucleotides.


Liver and pancreas facilitate digestion in the small intestines. Liver secretes bile, a substance that emulsifies fats and aid in its digestion. Pancreas secrete pancreatic juice containing a lot of digestive enzymes that function in the small intestines.

The secretions of the small intestine include amylase maltase, sucrase, lactase, etc. to digest carbohydrates and lipase to digest fats. Several other associated organs secrete chemicals into the small intestine to aid in digestion: the pancreas secretes enzymes like trypsin, chymotrypsin, and alkali solutions like bicarbonate as buffers and the liver and gall bladder make and secrete bile. Bile contains no enzymes, but salts to emulsify fat so it can be digested.

Absorption of completely digested food takes place in the ileum of the small intestines. The villi or the small fingerlike projections of the small intestines increase the absorption capacity of this organ.

The undigested food goes to the large intestines or colon. Water from the undigested particles is reabsorbed. Note that no digestion takes place in this organ. Storage in the large intestines lasts 12 to 1 hours before harmless bacterial grow abundantly.


The large intestine or colon, which begins with a blind pouch called the cecum. In humans, this terminates in the appendix, a finger-like extension which may function in the immune system. The large intestine functions to re-absorb (resorb) water and in the further absorption of nutrients. The bacterial flora of the large intestine includes such things as Escherichia coli, Acidophilus spp., and other bacteria, as well as Candida yeast (a fungus). These bacteria produce methane (CH4), hydrogen sulfide (H2S), and other gases as they ferment their food. Occasionally, some of this gas is released as flatus. As these bacteria digest/ferment left-over food, they secrete beneficial chemicals such as vitamin K, biotin (a B vitamin), and some amino acids, and are our main source of some of these nutrients.

The rectum is the terminal portion of the large


intestine and functions for storage of the feces, the wastes of the digestive tract, until these are eliminated. The external opening at the end of the rectum is called the anus. The anus has two sphincters, one voluntary and one involuntary. The pressure of the feces on the involuntary sphincter causes the urge to defecate and the voluntary sphincter controls whether a person defecates or not.

Functional Types of Movements in the Gastrointestinal Tract

There are two basic types of movements occur the gastrointestinal tract

1. Mixing movements, which keep the intestinal contents thoroughly mixed at all times.

2. Propulsive movements, cause food to move forward along the tract at an appropriate rate for digestion an absorption

The Mixing Movement is caused by local contraction of small segments of the gut wall. These movements are modified in different parts of the gastrointestinal tract for proper performance.

The propulsive movements in the gut are peristaltic. A contractile ring appears around the gut and then moves forward.


Peristalsis is an inherent property of any synctial smooth muscle but stimulation at any point causes a contractile ring to spread in both directions. Thus, peristalsis occurs in gastrointestinal tract, the bile ducts, other glandular ducts through the body, the ureters and most major smooth muscle tubes of the body.

Major Functions of the Stomach

1. Storage of large quantities of food until it can be accommodated in the lower portion of the gastrointestinal tract

2. Mixing of this food with gastric secretion until it forms a semi fluid mixture called chime

3. Slow emptying of the food from the stomach into small intestines at a rate suitable for proper digestion and absorption by the small intestine. Physiologically, the stomach can be divided into corpus and antrum.


Storage Function of the Stomach

As food enters the stomach, it forms concentric circles in the boy of the stomach, the newest food lying close to the esophageal opening and the oldest food lying nears the wall of the stomach. The stomach has relatively little tone in its muscular wall so that it can bulge progressively toward, thereby accommodating greater and greater quantities of food up to a limit of about 1 liter.

Mixing in the Stomach

The digestive juice of the stomach is secrete by the gastric glands, which cover almost the entire outer wall of the body of the stomach. These secretions come immediately into contact with the stored food lying against the mucosal surface of the stomach. When the stomach is filled, weak constrictor waves, also called mixing wave moves along the stomach wall approximately once every 20 seconds. These waves move the gastric secretions in the outermost layer of food gradually toward the antral part of the stomach. On entering the antrum, the waves become even stronger and the food and gastric secretions also become mixed to greater and greater degree of fluidity.


Peristalsis also contributes to mixing. Each time a peristaltic wave passes over the antrum towards the pylorus, it digs deeply into the contents of the antrum. The opening of the pylorus is small enough the only a few milliliters of antral contents are expelled into duodenum with each peristaltic wave, In backward though the peristaltic ring the moving peristaltic constrictive ring, combines with this reflux actions, in an exceedingly important mixing mechanism of the stomach.

Chyme. After the food has become mixed with the stomach secretion the resulting mixture that passes down the gut is called chyme. The degree of fluidity of chyme depends on the relative amounts of food and stomach secretion and on the degree of digestion that has occurred. The appearance of chyme is that of a murky, milky semi fluid paste

Propulsion of Food Through the Stomach.

Strong peristaltic waves occur about 20 percent of the time in waves, like the mixing waves, occurs about once every 20 seconds. As the stomach becomes progressively more and more empty, these intense waves begin farther and farther up the body of the stomach gradually pinching of the lowermost proteins of stored food, adding his food to the chyme in the antrum.


The peristaltic waves often exert as much as 50 to 70 cm of water pressure, which is about six times as powerful as the usual mixing waves.

Emptying the stomach. Emptying the stomach is promoted by peristaltic waves in the antrum of the stomach and resistance of the pylorus to the passage of food opposed it. The pylorus normally remains almost but not completely closed because of mild tonic contraction. The rate of emptying of stomach is determined principally by the degree of activity of the antral peristaltic waves.

The degree of activity of he pyloric pump is regulated mainly by signals from the duodenum that depress pyloric pump activity. In general when excesses of volume of chyme or excess of certain types of chyme have entered the duodenum, strong negative feedback signals both nervous and hormones, and transmitted to the stomach to depress the pyloric pump. Thus the mechanism allows chyme to enter the duodenum only as rapidly as it can be processed by the small intestines.

Strong nervous signals are transmitted from the duodenum back to the stomach when the stomach emptied food into the duodenum. These signals probably play the most important role of all in deterring the degree of activity of the pyloric pup and therefore, also in


determining the rate of emptying of the stomach.

The enterogastiric reflex is especially sensitive to the presence of irritant and acids in the duodenal chyme. For instance, any time the pH f the chyme in the duodenum falls below approximately 3.5 to 4, the enterogastic reflex is immediately elicited, which inhibits the pyloric pump and reduces or even blocks further the reflex acidic stomach contents in the duodenum until the duodenal chyme can be neutralized by pancreatic and other secretions

Breakdown of protein digestion will also elicit this reflex by slowing the rate of stomach emptying, sufficient time is insured for adequate protein digestion in the upper portion of the small intestines.

When fatty foods, especially fatty acids, are present in the chyme that enters the duodenum, the activity of the pyloric pump is depressed and stomach emptying is correspondingly slowed. This plays an important role in allowing slow digestion of the fats before they proceed into the deeper accesses of the intestine.

Emptying of the stomach is controlled to a moderate degree by stomach factors such as the degree of


filling in the stomach and the activity of the stomach peristalsis.

Probably, the more important control of stomach emptying, besides the feedback signal from the duodenum, include especially the enterogastric reflex and at a lesser extent hormonal feedback. These two feedback signals work to slow down the rate of emptying when too much chyme is at the small intestine, or the chyme is excessively acidic, or there’s too much protein, or if it is hypotonic or hypertonic, or there is irritation.

In this way, the rate of stomach emptying is limited to the amount of chyme that the small intestines can process.

Summary of Control Mechanism

1. Both nervous and hormonal input regulate the activity of the GI tract.The nervous mechanisms control

appetite and peristalsis, and the hormonal factors consist of three hormones secreted by tissues of the GI tract. These regulate gastric secretion and motility, pancreatic secretion, and gallbladder contraction. One example of nervous control of the GI tract is the swallowing reflex.

When food reaches the back of the mouth, pressure sensitive nerve cells send nerve impulses to the medulla of the


brain. The medulla coordinates a series of 25 muscles in the throat and esophagus which force the food toward the stomach in an automatic wave of contraction. The entire wave requires nine to ten seconds to complete, and is so well coordinated that one can swallow while upside down. The glottis is a muscular structure at the top of the trachea that closes during swallowing to prevent food from entering the lungs, and two sphincters open and close during contraction to keep food in the stomach.

2. The second nervous control is the coordination of smooth muscle contractions that produce peristalsis in the GI tract. This includes external nerve input from the autonomic nervous system, and internal control of the tract by a nerve plexus within the tract tissue. External nerves also exert control over the function of related glands such as the pancreas and salivary glands. Autonomic Control of the Gastrointestinal Tract.

The gastrointestinal tract receives extensive parasympathetic and sympathetic innervations that are capable of altering the overall activity of the entire gut or of the specific parts of it, particularly of its upper end down to the stomach and


its distal end from the mid-colon region to the anus.

Parasympathetic Innervations.

The parasympathetic supply to the gut is divided into cranial and sacral division, it causes general increase in activity of the mesenteric plexus which excites the gut wall and facilitates most of the intrinsic excitatory nervous reflexes of the gastrointestinal tract.

Sympathetic Innervations. Stimulation of the sympathetic nervous system inhibits activity in the gastrointestinal tract causing effects essentially opposite to those of the parasympathetic system. Thus, strong stimulation of the sympathetic system can totally block movement of the food through the gastrointestinal tract.

Application

1. GASTRITIS. Most of us occasionally suffer from

gastritis (inflammation of the stomach lining) with the familiar symptoms of stomachache and "heartburn." The pain is caused when food remains for too long a period in the stomach and excess hydrochloric acid is secreted.

Heartburn has nothing to do with the heart, but instead refers to the pain that is produced when some of the acidic material enters the lower end of the


esophagus and irritates esophageal tissues. These conditions can occur when one is under stress, or has eaten too much, since both cause decreased gastric motility.

The usual treatment for gastritis is to swallow a buffering compound (antacid) such as sodium bicarbonate, which buffers the acid in the upper part of the stomach and thereby relieves the pain. Since not everyone should take bicarbonate, due to its high sodium content, a number of commercial antacids have been developed that contain more complex mixtures of buffering compounds.

2. ACHYLIAOccasion the stomach has the

opposite disorder in which insufficient hydrochloric acid is secreted. This condition is called achylia and is estimated to occur in about 10% of the population. The symptoms are usually mild, and arise from too rapid evacuation of the stomach so that digestion is poor. The usual treatment is to acidify the stomach by hydrochloric or glutamic acid taken with meals.

3. ULCERIn a few people, gastrointestinal

disorders can become chronic, and the stomach or duodenum becomes locally inflamed and finally produces a crater-like sore called an ulcer.

In rare instances, the ulcer becomes so large that it hemorrhages or


even perforates the stomach lining so that stomach contents enter the abdominal cavity. This condition represents a medical emergency and requires immediate surgery and hospital care.

For simple ulcers, the treatment involves a diet of bland, readily digestible foods, and avoidance of stressful situations. In more serious ulcers that do not respond to dietary changes, a drug called cimetidine is useful. This compound works by blocking the histamine response of gastric tissue that would otherwise trigger a more widespread inflammation and increased gastric secretion. In about 75% of patients treated with cimetidine, relief of ulcer pain occurs in a few days and the ulcer is healed in four to six weeks.

4. DIARRHEAThere are several common conditions

of the GI tract associated intestinal motility. In diarrhea, the intestine responds to inflammation by constant peristalsis.

The inflammation can arise either through some toxic substance in the diet, as in food poisoning, or by viral or bacterial infection of the intestinal tissues. As a result food moves through the tract far to~ rapidly. The feces are fluid because the large intestine does not have a chance to remove water.

Usually diarrhea is self-limiting but in some circumstances it can be seriously debilitating. For instance, the


diarrhea associated with cholera can produce death through dehydration and loss of salt from the body. Drugs are available that control diarrhea by reducing intestinal motility.

5. APPETITE REGULATION Appetite is regulated by the central nervous system, and is probably related to nutrient levels circulating in the blood, such as glucose and lipid.

The receptors are in the hypothalamus of the brain, such that the sensation of hunger is activated when nutrient levels are relatively low. Other factors, not yet completely understood, also control to the regulation of appetite and food intake.

6. STOMACH CONTROL ON RATE OF DIGESTIONThe activity of the stomach

controls the rate at which food is presented to the intestine for digestion, although some digestion of occurs in the stomach as well. Hormones exert both stimulating and inhibiting effects on gastric juice. When food reaches the stomach, gastrin is secreted by cells in the terminal portion of the stomach and travels via the blood stream to the rest of the stomach, where it stimulates motility and secretion of gastric juice. The motility, in the form of peristaltic contractions, squeezes small quantities of food into the upper intestine.

7. CHOLECYSTOKININ AND SECRETIN


When food from the stomach reaches the upper intestinal segment called the duodenum, other cells of the intestine secrete cholecystokinin (CCK) and secretin.

Amino acids and fatty acids in the food activate CCK release, which stimulates the gall bladder to contract and inject bile into the small intestines. Stomach acid activates the release of secretin, which in turn travels to the pancreas by way of the blood to stimulate secretion of pancreatic juice.

Both CCK and secretin tend to inhibit gastric activity. Thus if a meal is high in fat and protein, it requires a longer time to digest. The amino acid and fatty adds cause a relatively large amount of CCK to be secreted so that gastric activity is slowed and thereby increasing digestion time. Similarly, higher stomach acid content in the food reaching the intestine causes grater release of pancreatic juice, the juice contains bicarbonate, which acts as buffer to neutralize stomach acid.

8. UNUSUAL FOOD ARE UNDIGESTEDUptake of digested nutrients is

controlled by carrier enzymes in the cell membranes of the intestinal epithelial tissue. Each enzyme is specialized to deal with specific nutrient which can be used by the body therefore unusual


substances in the diet tend not be absorbed, but instead are passed into fecal materials

Other abnormalities associated with the digestive system are:

1. Belching is when swallowed gas moves up the esophagus and is released from the mouth and/or nose

2. Vomiting is an important reflex to protect from harmful substances. Illnesses like flu, extreme pain (anywhere in the body: migraine, kidney stones. . .), and other stressful conditions can trigger the emptying of the stomach contents.

3. Hiatal hernia is caused in part by failure of the cardiac sphincter to close properly allowing stomach acid to enter and burn the esophagus.

4. An ulcer is when the gastric secretions eat through stomach (gastric ulcer) or intestinal wall (duodenal ulcer).

5. Diarrhea is having very loose, watery feces and constipation is having larger, harder, nearly dry feces. Getting enough fiber is importance to proper intestinal functioning because it holds water in the feces. If feces are too dry and hard, they will pass through the digestive tract with difficulty, possibly leading to diverticulosis or diverticulitis. Also, due to the increased transit time, there is


more time for bacteria to ferment the left-overs and secrete increased amounts of carcinogenic byproducts, thereby increasing the person’s chances of colon cancer.

Questions and Answers

What determines the essential nutrients of an animal?

The diet of each type of animal must include a specific group of essential nutrients-essential amino acids, essential fatty acids, vitamins and minerals – to provide the raw materials needed to synthesize the different kinds of organic molecules the animal must have to sustain life. The essential nutrient materials the animal must have but cannot synthesize in its cells. The nutrients that are essential differ for each type of animal because the ability to synthesize particular molecules is a genetic trait acquired through natural selection and because each type of animal has a unique evolutionary history.

In general, the more simple and primitive animals are able to synthesize more of the materials they require than can the more complex and advanced animals. The ability to construct many materials was lost during the evolution of more complex animals because the materials became so commonly available in the diet, that the enzymes required to synthesize them were no longer necessary


and were lost from the genetic repertoire.

For example, most vertebrate animals are able to synthesize vitamin C in their cells, but this ability has been lost in guinea pigs, fruit-eating bats, a few types of bird, and some other primates. All animals require vitamin C for it is essential in the construction and maintenance of substances that bind cells together, especially in skin, bone and muscle. The only animals that require vitamin in their diets, however, are those with ancestors that regularly consumed an adequate supply of vitamin c and gradually lost the enzyme necessary for its synthesis.

Why do malnourished children usually have enlarged abdomens?

A swollen abdomen and leg are symptomatic of severe protein, deficiency, In such cases, the blood does not contain enough plasma proteins to hold water in the blood vessels and water seeps out of the capillaries and accumulates in the interstitial fluids between cells, especially in the abdominal cavity and legs. This conditions also produces low blood pressure and cause the problems associated with poor blood circulation. In parts of Africa a child with an enlarged abdomens is said to kwashiorkor, which means “ the rejected one, because protein deficiency begins when a child is


weaned after a younger sibling is born, without the protein-rich milk from its mother, a child in a poverty-stricken area is likely to suffer form an inadequate protein intake.

What is the advantage of a digestive tract as compared with digestive cavity?

A digestive cavity or incomplete digestive system has only one opening to the outside environment. A digestive tract or complete digestive system has tow openings, one for food intake and the other for waste removal. Cnidarians, flatworms and other acoelomates have digestive cavities 9 the gastrovacular cavity) Advanced animals including both pseudocoelomates and coelenterates, have digestive tracts.

Food enters a digestive cavity by way of the single opeing, whichis ofhten ringed with special structures to poison the prey and so keep it form stuggling and injuring tissue inside the cavity. The food then moves into the cavity, where it is digested, the portions of food that cannot be digested are moved out of the body through the cavity, where it is digested. The portions of food that cannot be digested are moved out of the body through the same opening in the form of feces. Because the digestive cavity has a single opening, food entering the


cavity cannot be separated form the feces leaving the cavity. To prevent food and feces from mixing food is not taken in at the same time the feces leave- a restriction that limits the rate of food intake.

A digestive tract founding most animals, is a muscular tube with tow openings, one for food intake, the mouth and the other for feces removal (the anus) the one way system permits food to be ingested and held which fecal material is collected and expelled at the same time. The one-way flow also enables each segment of the tract to be specialized for performing a particular function o food passes through a sort of assembly line form mouth to anus. The degree of this specialization is greater in the vertebrate digestive tract, which consist of specific region of different functional initial preparation of food, storage, digestion, absorption and formation and removal of feces. Each region is separate form the other by special circular muscle, called sphincters, that can contract to close off the region of the tract.

How do the digestive tract of carnivores differ from those of herbivores?

Animal meat requires more storage and less processing than plant materials. The teeth of a carnivore are pointed and sharp for killing it preys and tearing it


into pieces small enough to swallow. Animal meat does not requires chewing. The teeth of a herbivore, by contrast are flat for crushing and grinding plant materials. S mammal cannot digest cellulose and so derives not nutrient from plant materials unless chewing ruptures the cells walls. A carnivore has a large stomach for food storage, since it reacts large and infrequent meals. The stomach of dog or cat makes up 70% of its digestive tract. An herbivore has smaller stomach because it eats smaller amount of food more frequently. The stomach of a horse makes up only about 8% of its digestive tract (a ruminant however, has an enormous stomach with several chambers, for digestion f cellulose by bacterial and protozoa. Most digestion and all absorption food take place in the small intestines and a carnivore, whose for requires less processing, has a shorter small intestine than an herbivore, whose food requires extensive processing.

What prevent the walls of the digestive tract from being digested?

Both the stomach and small intestine contain enzymes that can digest their own muscular walls. Yet this rarely happens, because the protein –digesting enzymes are not active until released into the lumen of the stomach or small intestine and the inner walls of these structures


are covered with a protective coat of mucus.

Digestive glands in glands in the pancreas and walls of the stomach secrete proteolytic enzymes (pepsin, trypsin, and chymotrypsin) as an inactive enzyme precursors, known generally as zymogens, the enzyme do not become active until they reach the lumen of the stomach or small intestine, thus, protein digestion does not occur in the glands, ducts or walls of the digestive system.

Active protein-digesting enzymes in the lumen of the digestive tract cannot digest the walls of the tract, because the walls are lined with a protective film of mucus that cannot be digested by enzymes. Occasionally, however the protective layer of mucus breaks lose and the walls of the stomach or small intestine are digested, two materials known to remove much are alcohol and aspirin, Emotional stress also leads to ulcers, usually duodenal ulcers, when the acidic gastric juicers are not immediately neutralized by bicarbonates as the juices enter the duodenum.

Why do cows have so many stomachs?

A cow has four stomach, rumen, reticulum, omasum and abomasum. The first three stomachs are pouches derived form the esophagus, and the abomasun is the true stomach. This unusual arrangement of the mammalian digestive tract found, only in ruminants, cud-chewing hoofed mammals


such as cows, sheep and deer is an adaptation for digesting the cellulose within plant cells. Cellulose is a polymer of glucose and an excellent source of energy. No mammal is able to synthesize an enzyme that digest cellulose, but ruminants digest it by harboring cellulose-digesting bacteria and protozoa within their stomachs.

The cellulose digesting microorganisms live in the rumen and reticulum of a cow, Swallowed food enters firs the rumen and then the reticulum where the microbes digest and ferment the liberated glucose, since condtions inside the stomachs are anaerobic, from the reticulum, the coarse plant materials are regurgitated or rechewed and then swallowed again for further enzymatic action. These microorganisms use the producers of their digestion and release fatty acids, which move to the omasum, along with some of the bacteria and protozoa. There the material is concentrated by reabsorption of water through the omasum walls and then is moved to the abomassum, where acids kill the microbes, in the small intestines, the microbes are digested and their amino acids, glucose and other monomers, together with fatty acids released earlier, are absorbed into the blood stream of the cow. The four stomachs of the ruminant enable part of the digestive tract to be more specialized than the digestive tracts of other herbivores of ridding of cellulose, for absorption and


recycle of water from the quantity of saliva use kind digestion by the microorganisms, and for killing of he microorganisms by acids.

Why do we have appendix?

An appendix is found only in humans, a few species of great apes and the wombat (a marsupisal). About 6 cm long and 1 cm in diameter, it is a hollow organ that dangles from the cecum,. The walls of the appendix are muscular and line first with a layer of lymph tissue, and then an innermost layer of epithelium It is structurally similar to the colon and is also capable of peristalsis. The appendix has no known function; we don not know why humans have one. Since it vaguely resembles a lymph node, the appendix may function to prevent intestinal infections

Appendix or inflammation of the appendix is the most common cause of emergency surgery today, the appendix becomes a liability when its lumen becomes blocked by fecal material or by swelling of the lymph tissue in reaction to an infection. Fluids secreted by the appendix then accumulate and become infected by intestinal bacteria, the areas then become inflamed, swollen and painful. If not removed, the appendix may burst and spread infection throughout the abdominal cavity.


RESPIRATORY SYSTEM

The respiratory system supplies oxygen to the tissues and removes carbon dioxide The major functional events of respiration include pulmonary ventilation, diffusion of oxygen and carbon dioxide between the blood and alveoli, transport of oxygen and carbon dioxide to and from the peripheral tissues, and regulation of respiration.

Pulmonary Ventilation

Lung volume increases and decreases as the thoracic cavity expands and contracts. The lung is held to the thoracic wall as if glued, except that they can slide freely in the thoracic cavity. Any time the length or thickness of the thoracic cavity increases or decreases, simultaneous changes in lung volume occur. The lungs can be expanded and contracted into ways (1) by downward and upward movement of the diaphragm to lengthen or shorten the chest cavity and (2) by elevation and depression of the ribs to increases and decrease the antero-posterior diameter of the chest cavity.

Raising and lowering the rib cage cause the lungs to expand and contract. In the natural resting position, the ribs


slant downward, allowing the sternum to fall backward towards the vertebral column. When the rib cage is elevated, the ribs project almost directly forward and way from the spine, increasing the anteroposterior thickness of the chest. Muscles the raise the rib cage are sternocleidomastoid, anterior serrati. and scaleni. While the muscles that depress the rib cage are abdominal recti and internal intercostals.

Pressures that cause Movement of Air in and out of the Lungs

Pleural pressure is the pressure of the fluid in the narrow space between the lung pleura and chest wall pleura. During normal inspiration, the expansion of the chest cage pulls the surface of the lungs with greater force.

Alveolar pressure is the air inside the lung alveoli. During inspiration, the pressure in the alveoli decreases to about negative one centimeter of water. This slight negative pressure is sufficient to move about 0.5 liter of air into the lungs within 2 seconds required for inspiration. During expiration opposite changes occur. The alveoli pressure rises to about +1 cm of water and these forces the 0.5-liter of inspired air out of the lungs during the 2-3 seconds of expiration.


Lung compliance is the change in lung volume for each unit change in transpulmonary pressure. Transpulmonarv pressure is the difference in pressure between the alveolar pressure and pleural pressure.

Surface Tension and Collapse of the Lungs

Water molecules have a strong attraction for one another. The water lining the alveoli also attempting to contract. This attempts to force the air out of the alveoli through the bronchi and in doing so it causes the alveoli to attempt to collapse. The net effect is to cause an elastic contractile force of the entire lungs, which is called the surface tension elastic force.

Surfactant reduces the work of breathing by decreasing the alveolar surface tension. Smaller alveoli have a greater tendency to collapse. When the alveoli have one-half of the normal radius, the collapse pressure are double. Surfactant, interdependence, and lung fibrous tissues are important for stabilizing the sizes of the alveoli. If some of the alveoli were small and others were large, theoretically the smaller alveoli would tend to collapse, decreasing their volume in the lungs. This loss of volume would cause expansion of the larger alveoli. But interdependence, fibrous tissue and surfactant are reasons why that


instability of alveoli does not occur in the normal lung.

Pulmonary Volumes and Capacities

Pulmonary volumes and capacities are measured with a spirometer, which is a drum that is inverted in water with a tube extending from the air space in the drum to the mouth of the person being tested.

The pulmonary volumes added together equal the maximum volume to which the lungs can be expanded. The four pulmonary volumes are: (1) tidal volume; which is the volume of air inspired or expired with each normal breath, (2) inspiratory reserve volume; the extra volume of air that can be inspired over and above the normal tidal volume, (3) expiratory reserve volume; the extra amount of air that can be expired by a normal tidal expiration, (4) residual volume; is the volume of air remaining in the lungs after the most forceful expiration.

Pulmonary capacities are combinations of two or more pulmonary volumes, which can be described as (1) Inspiratory capacity which is the combination of tidal volume and the inspiratory reserve volume, (2) Functional residual capacity, equals the expiratory reserve volume plus the residual volume, (3) Vital capacity,


equals the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume, (4) total lung capacity, it is equal to the vital capacity plus the residual volume.

Functions of the Respiratory Passageway

Air is distributed to the lungs by way of the trachea, bronchi and bronchioles. The trachea is called the first generation respiratory passageway, and two main rights and left bronchi are the second generation respiratory passageways; each division thereafter is an additional generation. There are between 20-25 generations before the air finally reaches the alveoli.

Respiratory Functions of the Nose

Warming and humidifying the air, ordinarily, the temperature of the inspired air rises to within one degree Fahrenheit of body temperature and within 2-3 % of flail saturation with water vapor before it reaches the trachea.

Filtering the air, the hairs at entrance to the nostrils are important for filtering out large particles. The air passing through the nasal passageway hits many obstructing veins: the conchae. septum, and pharyngeal wall. When the particles strike the surfaces of the obstructions, they are entrapped in the mucous coating.


Pressures in the Pulmonary System

Blood pressure in the pulmonary circulation is low compared with those in systemic circulation. The left atrial pressure can be estimated by measuring the pulmonary wedge pressure. The pulmonary wedge pressure can be measure by floating a ballogn4ipped catheter through the right heart and pulmonary artery until the catheter wedges tightly in smaller branches of the artery. The wedge pressure is usually only 2-3 mm.Hg greater than the left atrial pressure. Pulmonary pressures are (1) pulmonary artery pressures; (2) pulmonary capillary pressure and (3) left atrial and pulmonary venous pressure.

Effect of Hydrostatic Pressure Gradients in the Lungs in the regional Pulmonary Blood flow

Hydrostatic gradients in the lung create three zones of pulmonary blood flow. Zone I has no blood flow during any part of the cardiac cycle because the local capillary pressure never rises higher than the alveolar pressure. Zone 2 has an intermittent blood flow that occurs during systole~ when the artery pressure is greater than the alveolar pressure. Zone 3 has a high continuous blood flow because the capillary pressure remains greater than the alveolar pressure during the entire cardiac cycle.


PHYSICAL PRINCIPLES OF GAS EXCIIANGE;DIFUSION OF OXYGEN AND CARBON DIOXIDETHROUGH THE RESPIRATORY MEMBRANE

Respiratory Gases Diffuse from Areas of High Partial Pressure to Areas of Low Partial Pressure. Respiratory physiology involves mixture of gases, mainly Oxygen, Nitrogen, and Carbon Dioxide. The rate of diffusion of each of these gases is directly proportional to the pressure to the pressure caused by each gas alone, which is called the partial pressure of the gas. Partial pressures are used to express the concentrations of gases because it is the pressures that causes the gases to move via diffusion from one part of the body to another. The partial pressures of oxygen, carbon dioxide, and nitrogen are designated as P02, PC02, and PN2, respectively.

The pressure of gas in the air is calculated by multiplying its fractional concentration by the total pressure. Air has a composition of about 79% nitrogen and about 21% oxygen. The total pressure at sea level (atmospheric pressure) averages 760 mm Hg; therefore 79% of the 760 mm Hg is caused by nitrogen (about 600 mm Hg) and 21 Hg is caused by oxygen (about 160 mm Hg). The partial pressure of nitrogen Ill the mixture is 600 mm Hg, and the partial pressure of oxygen is 160 mm Hg; the total pressure is 760 mm Hg,


the sum of the individual partial pressures.

The pressure of gas in a solution is determined not only by its concentration but also by its solubility coefficient. Some types of molecules, especially carbon dioxide, are physically or chemically attracted to water molecules, which allows far more of them to become dissolved without a build-up of excess pressure within the solution. The relationship between gas concentration and gas solubility is expressed by Henry's Law:

Concentration of dissolved gasPressure = Solubility Coefficient

The vapor pressure of water at body temperature is 47 mm Hg.

When air enters the respiratory passageway, water evaporates from the surfaces and humidifies the air. The pressure that the water molecules exert to escape from the surface is the vapor pressure of the water, which is 47 mm Hg at the body temperature. Once the gas mixture has become fully humidified, the partial pressure of water vapor in the gas mixture is also 47 mm Hg. This Partial pressure is designated PH2O.

The rate of gas diffusion in a fluid (D)' is affected by multiple factors. These factors are described as follows


and expressed in the following single formula:

Pressure difference the greater the difference in pressure between the two ends of a diffusion pathway, the greater is the rate of gas diffusion.

Cross-sectional area (A) - the greater the cross-sectional area of the diffusion pathway, the greater is the total number of molecules to diffuse.

Gas solubility (S) the greater the solubility of the gas, the greater is the number of m6lecules available to diffuse for any given pressure difference.

Diffusion distance (d) - the greater the distance that the molecules must diffuse, the longer it takes the molecules to diffuse the entire the distance.

Molecular weight of gas (MW) - the greater the velocity of kinetic movement of the molecules, which i~ inversely proportional to the square root of the molecular weight, the greater the rate of diffusion of the gas.

Temperature - the temperature remains reasonably constant in the body an4 usually need not be considered.

The diffusion coefficient of a gas is directly proportional to its solubility and inversely proportional to its


molecular weight. It is obvious from the above formula that the characteristics of the gas determine two factors of the formula - solubility and molecular weight-and together they determine the diffusion coefficient of the gas. That is, the diffusion coefficient is proportional to SVMW'~; also, the relative rates at which different gases at the same pressure levels diffuse are proportional to their diffusion coefficients. Considering the diffusion coefficient for oxygen to be 1, the relative diffusion coefficient for carbon dioxide is 20.3. The diffusion coefficient for nitrogen, carbon monoxide, and helium are less than that of oxygen.

COMPOSITION OF ALVEOLAR AIR-IT'S RELATION TO ATMOSPHERIC AIR

The concentrations of gases in alveolar air are different than those in atmospheric air. These differences are shown in the table. And explained as follows:

1. Alveolar air is only partially replaced by atmospheric air with each breath.

2. Oxygen is constantly being absorbed from the alveolar air

3. Carbon dioxide is constantly diffusing from the pulmonary blood into the alveoli.


4. Dry atmospheric air is humidified before it reaches the alveoli.

Water vapor dilutes the other gases in the inspired air. Atmospheric air is composed mostly of nitrogen and oxygen; it contains almost of nitrogen and oxygen; it contains almost no carbon dioxide or water vapor. The atmospheric air becomes totally humidified as it passes through the respiratory passages. The water vapor at normal body temperature (i.e. 47 mm Hg) dilutes the other gases in the inspired air. the oxygen Hg in atmospheric air to 249 mm Hg in the humidified air, and the nitr6gen partial pressure decreases from 597 to 5634 mm Hg

Alveolar air is renewed very slowly by atmospheric air. The amount of alveolar is replaced by new atmospheric air with each breath is only one seventh of the total, so that many breaths are required to completely exchange the alveolar air. This slow replacement of alveolar air prevents sudden change in gas concentrations in the blood; makes the respiratory control mechanisms much mire stable that it would otherwise be; and helps prevent excessive increases and decreases in tissue oxygenation, tissue carbon dioxide concentration, and tissue pH when respiration is temporarily interrupted.


The alveolar oxygen concentration is controlled by the rate of oxygen absorption into the blood and the rate of entry of new oxygen into the lungs. Oxygen is continually being absorbed into the luings, and new oxygen is continually being breathed into the alveoli. The more rapidly oxygen is absorbed, the lower becomes its concentration in the alveolus. In comparison, the more rapidly oxygen is breathed into the alveoli from the atmosphere, the higher its concentration.

Expired air is a combination of dead space air and alveolar air. The overall composition of expired air is determined by the proportion of the expired air that is dead space air and the proportion of the expired air that is alveolar air. When air is expired by the lungs, the first pr6portion of this air (dead space air) is typical humidified air. Then, more and more alveolar air becomes mixed with the dead space air until all the dead space air has been washed out and only alveolar air is expired at the end of expiration.

DIFFUSION OF GASES THROUGH THE RESPIRATORY MEMBRANE

A respiratory unit is composed of respiratory bronchiole, alveolar ducts, atria, and alveoli. There are about 300 million units in the two things. The alveolar walls are


extremely thin, and within them is an almost solid network of interconnecting capillaries; the flow of blood in the alveolar wall has been described as a sheet" of flowing blood. Gas exchange occurs through the membranes of all the terminal portions of the lungs, not merely ran the alveolar themselves. These membranes are collectively known as the respiratory membrane, or the pulmonary membrane.

The respiratory membrane is composed of several different layers The exchange of oxygen and carbon dioxide from the blood and alveolar air requires diffusion through the different layers of the respiratory membrane:

A layer of fluid lining the alveolus that contains surfactant

The alveolar epithelium, which is composed of thin epithelial cells.

Diffusion coefficient-The diffusion coefficient for the transfer of each gas through the respiratory membrane depends on its solubility in the membrane and, inversely, on the square root of its molecular weight.

Pressure difference across respiratory membrane- The difference between the partial pressure of gas in the alveoli and that of gas in t'1he blood is directly proportional to the rate of gas transfer through the membrane.


DIFFUSING CAPACITY OF THE RESPIRATORY MEMBRANE

The diffusing capacity of the lungs for. carbon dioxide is 20 times greater than that of oxygen. The ability of the respiratory membrane to exchange a gas between the alveoli and the pulmonary blood can be expressed in quantitative terms by its diffusing capacity, which is defined as the volume of a gas that diffuses through the membrane each minute for a pressure difference of one mm Hg. The diffusing capacity of the lungs for oxygen when a person is at rest is about 21 ml/mm Hg in minute. The diffusing capacity for carbon dioxide is about 20 times this value, or about 440 ml/mm Hg/minute.

The diffusion capacity for oxygen increases during exercise. During exercise, the oxygenation of 'the blood is increased not only by greater alveolar ventilation but also by greater capacity of the respiratory membrane for transmitting oxygen into the blood. During strenuous exercise, the diffusing 'capacity for oxygen can increase to about 65 ml/ mm Hg, which is three times the diffusing capacity during resting conditions. This increase is caused by the ff:

Increased surface area- Opening up of closed pulmonary capillaries or extra


dilatation of open capillaries increases the surface area for diffusion of oxygen.

Improved ventilation-perfusion ratio - Exercise improves the match between the ventilation of the alveoli and the perfusion of the alveolar capillaries with the blood.

Respiratory Membranes: An epithelial basement membrane A thin interstitial space between

the alveolar epithelium Capillary membraneA capillary basement membrane that

fuses in places with the epithelial basement membrane

The capillary endothelial membrane.

The respiratory membrane is optimized for gas exchange:

Membrane thickness--Despite the large number of layers, the overall thickness of respiratory membrane averages about 0.6 micrometer except where there are cell nuclei.

Membrane surface area-The total surface area of the respiratory membrane is about 70 square meters in the normal adult. This is equivalent to the floor area of a 25-by-30- foot room

Capillary blood volume-The capillary blood volume is 60 to 140 milliliters. By imagining that this in all amount of blood is spread


over the entire surface of a 25-by-30-foot floor, it is easy to understand the rapidity of respiratory exchange of gases.

Capillary diameter-The average diameter of the pulmonary capillaries is about 5 micrometers; the red blood cell membrane usually touches the capillary wall so that the oxygen and carbon dioxide need not pass through the significant amounts of plasma as they diffuse between the alveolus and the red cells.

Multiple factors determine how rapidly a gas will pass through the respiratory membrane. These determining factors include the ff:

Thickness of respiratory membrane-The rate of diffusion through the membrane is inversely proportional to the membrane thickness. Edema fluid in the interstitial space and alveoli decreases diffusion because the respiratory gases must move only through the membrane but also through this fluid. Fibrosis of the lungs can also increase the thickness of some portions of the respiratory membrane.

Surface area of respiratory membrane- In emphysema; many in the alveoli coalesce, with dissolution of alveolar walls: This often causes


the total surface area to decrease by as much as five folds. During strenuous exercise. Even the slightest decrease in surface area can be a serious detriment to respiratory exchange of gases.

TRANSPORT OF OXYGEN AND CARBON DIOXIDE IN THE BLOOD and BODY FLUIDS

OXYGEN is transported principally in combination with hemoglobin to the tissue capillaries, where it is released for use by the cells.

In tissue cells, oxygen reacts with various foodstuffs to form large quantities of carbon dioxide. This enters the tissue capillaries and is transported back to the lungs.

Pressures of Oxygen and Carbon Dioxide in the Lungs, Blood and Tissues

The P02 of pulmonary blood rises to equal that of alveolar air within the first third of the capillary

The P02 averages 104 mm Hg in the alveolus, whereas the P02 of venous blood entering the capillary averages only 40 mm Hg. The initial pressure difference that causes oxygen to diffuse into the pulmonary capillary is 104-40 mm Hg, or 64 mm Hg. The P02 rises to equal that of alveolar air by the time the blood has


moved a third of the distance through the capillary, becoming almost 104 mm Hg.

Tissue P02 is determines by the rate of oxygen transport to the tissues and the rate of oxygen utilization by the tissues.

The P02 in the initial portions of the capillaries is 95 mm Hg, and the P02 in the interstitial fluid surrounding the tissue cells averages 40 mm Hg. This pressure difference causes oxygen to diffuse rapidly from the blood into the tissues, and the P02 of the blood leaving the tissue capillaries is also about 40 mm Hg. Two main factors can affect the tissue P02.

1. Rate of Blood Flow. If the blood flow through a particular tissue becomes increase, greater quantities of oxygen are transported into the tissue in a given period, and the tissue P02 becomes correspondingly increased.

2. Rate of Tissue Metabolism. If the cells use more oxygen for metabolism than normal, the interstitial fluid P02 tends to reduce.

Carbon dioxide diffuses in a direction exactly opposite that of oxygen. There is one major difference between the diffusion of carbon dioxide and oxygen: carbon dioxide can diffuse about 20 times as rapidly as oxygen


TRANSPORT OF OXYGEN IN THE BLOOD

About 97 percent of the oxygen are carried to the tissues in chemical combination with hemoglobin

The remaining 3 per cent are carried to the tissues in the dissolved state in the water of the plasma and cells. Hemoglobin combines with large quantities of oxygen when the P02 level are low. When blood passes through the lungs, where the blood P02 rises to 95 mm Hg, hemoglobin picks up large quantities of oxygen. As it passes through the tissue capillaries, where the P02 falls to about 40 nm Hg, large quantities of oxygen are released from the hemoglobin. The free oxygen then diffuses to the tissue cells.

Carbon monoxide interferes with the oxygen transport because it has about 250 times the affinity of oxygen for hemoglobin

Carbon monoxide combines with hemoglobin at the same point on the hemoglobin molecule, as does oxygen and can therefore displace oxygen from the hemoglobin. Because it binds with about 250 times as much as tenacity as oxygen, relatively small amount of carbon monoxide can tie up a large portion of the hemoglobin, making it unavailable for oxygen transport. A patient with severe carbon monoxide poisoning can be helped by the administration of pure oxygen


because oxygen at high alveolar pressure displaces carbon monoxide from its combination with hemoglobin more effectively than does oxygen at low atmospheric pressures.

TRANSPORT OF CARBON DIOXIDE IN THE BLOOD

Under resting conditions, about 4 milliliters of carbon dioxide are transported from the tissues to the lungs in each 100 millimeters of blood

Approximately 70 percent of the carbon dioxide is transported in the form of bicarbonate ions, 23 percent is transported in combination of hemoglobin and plasma proteins, and 7 percent is transported in the dissolve state in the fluid of the blood.

Transport in the form of bicarbonate ions (70 %). Dissolved carbon dioxide reacts with water inside red blood cells to form carbonic acid. An enzyme in the red blood cells called carbonic anhydrase catalyzes this reaction. Most of the carbonic acid immediately dissociates into bicarbonate ions and hydrogen ions; the hydrogen ions in turn combine with hemoglobin. Many of the bicarbonate ions diffuse from the red blood cells into the plasma while chloride ions diffuse into the red blood cells to take their place, a phenomenon called the chloride shift.


Transport in combination with hemoglobin and plasma proteins (23%). Carbon dioxide reacts directly with amine radicals of the hemoglobin molecules and plasma proteins to form the compound carbaminohemoglobin. This combination of carbon dioxide with the hemoglobin is a reversible reaction that occurs with a loose bond, so that the carbon dioxide is easily released into the alveoli where the where the PC02 is lower than that in the tissue capillaries.

Transport in the dissolved state (7%). The amount of carbon dioxide dissolved in the fluid of the blood at 45-mm Hg is about 2.7 milliliters per 100 ml of blood (2.7 volumes percent). The amount dissolved at 40 mm Hg is about 2.4 ml, or a difference of ()~3ml. Therefore, only about 0.3m1 of carbon dioxide is transported in the form of dissolved carbon dioxide by each lOOml of blood; this represents about 7% of all carbon dioxide that is transported.

REGULATION OF RESPIRATION

Respiratory Center

1. The dorsal respiratory group – generates inspiratory action potentials in a


steadily increasing ramp-like fashion and thus is responsible for the basic rhythm of respiration

2. The pneumotaxic Center - helps to control the rate and pattern of breathing. It transmits inhibitory signals to the dorsal respiratory group and thus controls the filling phase of the respiratory cycle.

3. The ventral respiratory group - can cause either expiration or inspiration, depending on which neurons in the group are stimulated

The Hering - Breuer reflex prevents over inflation of the lungs. This reflex is initiated by nerve receptors located in the walls of the bronchi and bronchioles that detect the degree of stretch of the lungs. When the lungs become overly inflated, the stretch receptors activate an appropriate feedback response that "switches off' the inspiratory ramp and thus stops further inspiration.

Chemical Control of Respiration

1. The ultimate goal of respiration is to maintain proper concentrations of oxygen, carbon dioxide, and hydrogen ions in the tissues. Excess carbon dioxide or hydrogen ions mainly stimulate the respiratory center itself, causing increased strength of inspiratory and expiratory signals to the respiratory muscles.


2. Increased PCO2 or hydrogen ion concentration stimulates a chemosensitive area of the respiratory center. The sensor neurons in the chemosensitive neurons compared with carbon dioxide.

Regulation of Respiration during Exercise

1. In strenuous exercise, the arterial P02, PC02 and pH values remain almost exactly normal. Strenuous exercise can increase oxygen consumption and carbon dioxide formation by as much as 20-fold.

2. Chemical factors can also play a role in the control of respiration during exercise. When a person exercises, the nervous factors usually stimulate the respiratory center by the proper amount to supply the extra oxygen requirements for the exercise and the blow off the extra carbon dioxide.

Other factors that affect Respiration

1. Voluntary control - One can hyperventilate or hypoventilate to such an extent that serious derangement in PCO2, PH, and P02 can occur in the blood.

2. Irritant receptors in the airways - The epithelium of the trachea, bronchi, and bronchioles is supplied with sensory nerve endings called pulmonary irritant receptors that are


stimulated by some irritants that enter the respiratory airways.

3. Lung "J receptors" - a few sensory nerve endings occur in the alveolar wall in justaposition to the pulmonary capillaries, and they are called 3 receptors.

4. Brain edema - The activity of the respiratory center may be depressed or even inactivated by acute brain edema resulting from concussion.

5. Brain edema The activity of the respiratory center may be depressed or even inactivated by acute brain edema resulting from concussion.

6. Anesthesia - Perhaps the most prevalent cause of respiratory depression and respiratory arrest is overdose with anesthetics or narcotics.

Methods for Studying Respiratory Abnormalities

The most fundamental tests of pulmonary performance are determinations of the blood P02, PC 02, and pH. it is often important to make these measurements rapidly as an aid in determining the appropriate therapy for acute respiratory distress or acute abnormalities of acid-base balance. Measuring devices for pH, PCO2, and P02, are built into the same apparatus, and all these measurements can be made within a minute or so with one small sample of blood; thus, changes in the blood gases Notes in Animal Physiology by CCDivina………… 68

and pH can be followed almost moment by moment.

Respiratory Disorders

Chronic Pulmonary Emphysema

The term pulmonary emphysema literally means excess air in the lungs. Chronic pulmonary emphysema, however, signifies a complex obstructive and destructive process of the lungs and is usually a consequence of long-term smoking The following pathophysiological events contribute to its development:

· Chronic infection the bronchi and bronchioles are irritated. The irritant (usually smoke) deranges the normal protective mechanisms of the airways: (1) cilia may be partially paralyzed so that mucus cannot be moved easily out of the passageways, (2) secretion of excess mucus exacerbates the condition, and (3) alveolar macrophages can be inhibited.

· Airway obstruction - the infection, excess mucus, and inflammatory edema of the bronchiolar epithelium combine to cause chronic obstruction of many of the smaller airways.

· Destruction of alveolar walls - the obstruction of the airways makes it especially difficult to expire, causing entrapment of air in the alveoli and over stretching of the


alveoli. This, combined with lung infection, causes marked destruction of the alveolar cells.

Pneumonia

The term pneumonia includes any inflammatory condition of the lung in which alveoli are filled with fluid and blood cells. A common type of pneumonia is bacterial pneumonia, caused most frequently by pneumococci. This disease begins with infection in the alveoli; the pulmonary membrane becomes inflamed and highly porous, so that find and even red and white blood cells pass out of the blood into the alveoli. The infected alveoli become progressively filled with fluid and cells, and the infection spreads by extension of bacteria from alveolus to alveolus. Eventually, large area of the lungs, sometimes whole lobes or even a whole lung, become "consolidated" which means that they are filled with fluid and cellular debris.

Some Questions and Answers

What is respiration? Why do animals respire and why is it important?

Respiration is the process by which animals take in oxygen necessary for cellular metabolism and release the carbon dioxide that accumulates in their bodies as a result of the expenditure of energy. When an animal breathes, air or


water is moved across such respiratory surfaces as the lung or gill in order to help with the process of respiration. Oxygen must be continuously supplied to the animal and carbon dioxide, the waste product, must be continuously removed for cellular metabolism to function properly. For example, if this does not happen and carbon dioxide levels increase in the body, pH levels decrease and the animals may eventually die

Oxygen is valuable because it is important in many ATP-producing cycles occurring throughout the body such as, the Krebs cycle, and the electron transport chain. Glycolysis breaks down glucose, a six-carbon sugar, into the three-carbon molecule of pyruvic acid. The series of reactions associated with glycolysis are necessary for anaerobic and aerobic pathways to work, and are also the most fundamental in cellular metabolism. In the presence of 02, the pyruvic acid, which came about from the breakdown of glucose, is further oxidized. However, under anaerobic conditions the pyruvic acid is reduced to lactic acid. Glycolysis follows a specific pathway and ultimately, the oxidation of 1 mol of glucose to pyruvic acid ends in a net gain of only 2 mol of ATP and 2 NADH molecules.

The Krebs cycle is a series of eight major reactions following glycolysis. In these reactions, acetate residues are


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degraded to CO2 and H2O. With each turn of the Krebs cycle, 2 CO2 molecules and 8 H+ atoms are removed. These hydrogen atoms, which are removed two at a time, are transported by NADH and FADH2 and further go into the electron transport chain.

The electron transport chain, also known as the respiratory chain, oxidizes the NADH and FADH2 from the Krebs cycle to H2O by oxygen. This cycle involves electrons that move through about seven steps in order of their decreasing electron pressures, more specifically, from the high reducing potential of NADH to FADH2 to oxygen, the final electron acceptor. The electron transfer is the final pathway for all electrons during aerobic metabolism, and it uses the energy from the transfer for the phosphorylation of ADP to ATP. A total of 38 ATP molecules are collectively released from the three cycles of glycolysis, the Krebs cycle, and the electron transport chain working together. Without oxygen, the Kreb's cycle and electron transport chain would be disabled and only 2 ATPs would be produced by glycolysis. To maintain an adequate supply of oxygen to cells, animals must have an efficient means of gas transfer and respiration.

What is oxygen debt?


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In some animals, such as mammals, if the supply of oxygen to active muscle cells is not sufficient to produce enough ATP to maintain intense activity, the only source of additional ATP will be from glycolysis. Without sufficient oxygen, some of the pyruvic acid produced is reduced to lactic acid, which accumulates in the tissues, resulting in fatigue. Excess lactic acid may also enter the blood, decreasing blood pH and affecting other tissues in the body. When muscle activity decreases, extra oxygen is needed to convert the lactic acid back to pyruvic acid, which is then utilized by the Kreb's cycle. This extra oxygen represents the animal's oxygen debt. Some animals, such as the goldfish and some intertidal invertebrates, can avoid oxygen debt through the use of biochemical pathways that convert lactic acid to alcohol, which can then be excreted.

What is the difference between air and water as respiratory environments? How does this affect the amount of energy spent obtaining oxygen in water and air and therefore the structures used in ventilation?


Water and air are radically different as respiratory environments in a number of ways. The most significant difference is that water contains only 1/13 as much O2 as air does, or 1% to 21% (water to air) by volume. Water also is over 800 times denser than air and 50 times more viscous, so aquatic breathers must use more energy to simply move water across their respiratory surfaces. Fish, for example, use as much as 10% of the oxygen they take in to provide breathing muscles with enough oxygen to burn the energy needed to keep water passing over the gills in the right direction. Humans use only 1-2 % of their oxygen intake to keep breathing. Temperature also has an effect on the amount of oxygen each environment can hold. As water temperature increases the amount of dissolved oxygen decreases. Air also shows a slight reduction in oxygen content with increasing temperature, but it isn't physiologically significant because there is so much oxygen in air to begin with. Gas diffusion rates are also lower in water than in air. Salt water contains less oxygen than fresh water because the higher salt concentration decreases gas solubility. All of this produces a vast difference between aquatic and terrestrial organisms in the amount of energy expended to obtain oxygen.

How is oxygen carried through the blood and passed onto other cells?


What role does hemoglobin play in oxygen transfer? What conditions affect hemoglobin/oxygen affinity?

Hemoglobin (Hb) is found in red blood cells, being the principle part of a red blood cell. Hemoglobin is a large protein with four polypeptide chains and four heme groups. Each heme group has an iron atom attached to it, which is where oxygen attaches to be carried to cells and tissues. It is important to note that the O2/Fe bond, that is initially made so the oxygen can be transported, can be readily broken in the right conditions. These conditions are altered depending on if oxygen needs to be picked up or released to tissue cells. The reason hemoglobin is found in red blood cells only is that the conditions needed for efficient oxygen transport by the Hb molecules can be quickly changed, and all of this can be done without changing the conditions throughout the body. Some of the conditions necessary for oxygen and carbon dioxide transport may be unsuitable for other reactions that need to take place throughout the body, so keeping Hb within the red blood cells allows oxygen transport to occur without interfering with other bodily functions. Conditions that control the ability of hemoglobin (Hb) to bind to oxygen include the partial pressure of O2 in the surrounding respiratory medium (air or water), temperature, pH, CO2 levels. A high partial pressure of O2 in the


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surrounding respiratory medium will increase the rate at which the O2

diffuses into the blood. Hemoglobin's affinity for oxygen typically decreases if temperature increases, pH decreases, or CO2 levels increase.

There are a few different kinds of hemoglobin, all doing the same job, but each having its own affinity to O2. Normally hemoglobin will pick up an O2

when the partial pressure of the O2 in the blood (O2 dissolved in solution) is high, and there are fewer than 4 O2

molecules on the hemoglobin, 4 being the maximum number able to be carried. When an O2 molecule is attached to a hemoglobin molecule it is not affecting the partial pressure of the O2 in the blood, as there is a low concentration of O2 in the blood plasma, just not enough to supply the cells of the body. The best scenario for oxygen transfer from the lungs to body cells and tissues is hemoglobin to have high affinity at the respiratory surface (high amount of O2

diffusing across the lung surface) and low oxygen affinity (give the oxygen away) near body cells that need it (low O2 content).

Other factors that affect hemoglobin/oxygen affinity include a decrease in pH, which reduces hemoglobin/oxygen affinity (the Bohr effect). A decrease in pH reduces Hb/ O2

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binding sites of the hemoglobin molecule changes, making it more difficult for them to bind to oxygen. (See "Why are red blood cells important to carbon dioxide transport?" for a complete explanation of the mechanisms involved). A rise in body temperature reduces Hb/O2 affinity as the increased energy (heat) will prevent bonds from forming or break bonds currently in place. Increased CO2 content can affect the affinity because CO2 can bind to sites where O2 would normally bind. Hemoglobin normally picks up CO2 at the tissues and releases it at the respiratory surface in exchange for oxygen to complete the chain. When the concentration of CO2 is too high it takes the place of oxygen on Hb at higher than normal rates.

Oxygen dissociation curves graphically represent the percent of hemoglobin's oxygen binding sites that are holding oxygen at different partial pressures of oxygen. The sigmoid (S-shaped) curve is due to subunit cooperativity between the four oxygen binding sites on a hemoglobin molecule. When no binding sites are occupied by oxygen, it is relatively difficult to get the first oxygen to bind. After it does, however, the structure of the hemoglobin molecule is altered a bit, and the second binding site becomes more accessible. This makes it a bit easier for the second molecule of oxygen to bind. After this, additional oxygen


molecules bind rather easily to the third and fourth binding sites. Therefore, oxygen binds slowly at first, and then more quickly, giving the dissociation curve a sigmoid shape.

How is carbon dioxide transported in the blood?

The transportation of carbon dioxide is a very significant process of the gas-transfer systems within many animals. There are three main ways in which CO2 is transported in the blood. A small percentage of the CO2 that is in the blood is dissolved molecular CO2. A larger amount of CO2 reacts with –NH2

groups of hemoglobin and other proteins to form carbamino compounds. However, most of the CO2 that is transported in the blood is in the form of bicarbonate (HCO3

-). In general, CO2 is diffused into the blood from the tissues. The blood transports CO2 to the respiratory surfaces of the lungs or gills, where it is released into the environment. The blood mainly consists of plasma and erythrocytes (red blood cells). Most of the CO2 entering and leaving the blood does so through erythrocytes.

Why are red blood cells important to carbon dioxide transport?

Most of the CO2 entering or leaving the blood go through red blood cells for two reasons. One reason is due to the


enzyme carbonic anhydrase. This enzyme is present in red blood cells and not in the plasma. The enzyme is important in the transportation of CO2 because, within the red blood cells, it catalyzes the reaction of CO2 with OH- resulting in the formation of HCO3

- ions. As the level of HCO3

- ions increases within the erythrocytes, the HCO3

- ions diffuse through the erythrocyte membranes into the plasma of the blood. In order to maintain electrical balance within the erythrocytes, an anion exchange occurs in a process called a chloride shift. In this process, HCO3

- ions leave the red blood cells while a net influx of Cl-

ions from the plasma enters the red blood cells. The membrane of red blood cells is very permeable to both ions because the membrane has a high concentration of a special anion carrier protein, the band III protein. This protein allows for a passive diffusion of the Cl- and HCO3

-

ions to and from the red blood cells and plasma. This keeps the bicarbonate from building up in the red blood cells, which would slow down or stop the reversible conversion of CO2 to HCO3

-. Facilitated

diffusion occurs in the movement of CO2

across the respiratory surfaces as bicarbonate (HCO3

-) diffuses out of the red blood cells and into the epithelium where it is converted back to CO2. Excretion of CO2 is limited by the rate of bicarbonate-chloride exchange across the erythrocyte membrane.


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The second reason why most of the CO2 is transported to and from the blood by passing through the erythrocytes is that O2 binds to Hemoglobin (Hb) at the respiratory surface, causing hydrogen ions (H+) to be released. The increase in H+ ions combines with HCO3

- to form CO2 and OH-. Thus, more CO2 is formed and can leave the blood across the respiratory surface. Excess H+ binds to OH-, forming water and allowing the pH to increase enough to promote the binding of oxygen to Hb. The release of O2 from Hb in the tissues makes the Hb available to bind to H+, promoting the conversion of CO2 to HCO3

-, which helps draw CO2 from the tissues. Therefore, CO2 that is being transported into and out of the red blood cells minimizes changes in pH in other parts of the body because of proton binding to and proton release from hemoglobin, as it is deoxygenated and oxygenated, respectively (Figure 1.).


Why is the regulation of body pH important?

The regulation of body pH is important because some organs, tissues, and various types of cells are more affected by changes in pH than others. Therefore, within an animal’s body are various mechanisms, including mechanisms at the cellular level, that regulate the body pH in order for the animal to maintain normal bodily functions. For example, the regulation of body pH is needed in animals in order to stabilize volume of hydrogen ions and to regulate enzyme activity. Within cells, pH is regulated in order for cellular functions to proceed. At the tissue level, the body has the ability to redistribute acid


between body compartments because some tissues have the ability to tolerate much larger fluctuations in pH than others do. In general, animals have a body pH that is on the alkaline side of neutral, which means that there is less hydrogen than hydroxyl ions in the body. Human blood plasma, at 37 C (normal body temperature) has a pH of 7.4. Normal functioning can be maintained in mammals at 37º C over a blood plasma pH range of 7.0-7.8.

How does breathing regulate pH?

One of the main ways that a mammal regulates pH is through the control of respiration. For example, if the body pH in a mammal decreases, the respiration rate and depth of respiration increases in order to get rid of the excess CO2, which brings H+ levels back down and brings pH back up. Hence, when breathing is increased, CO2 levels in the blood decline and pH increases. If pH increases, respiration rate decreases, thereby increasing CO2 levels, which forms more carbonic acid and brings pH back down.

In mammals, a stable body pH is achieved by adjusting the release of CO2 through the lungs and excretion of acid or bicarbonate through the kidneys, so that acid excretion and production are balanced. The collecting duct of the mammalian


kidney has acid-excreting and base-excreting cells, which can be altered to increase or decrease acid or base excretion. In aquatic animals, the external surfaces have the capacity to extrude acid in similar ways to the collecting duct of the mammalian kidney. For example, a protein ATPase exists in the skin of frogs and gills of freshwater fish which excretes protons on the apical surface of the epithelium. Fish gills also have a HCO3

-/Cl- exchange mechanism, which aids in the regulation of body pH.

What are alkalosis and acidosis, and what are the consequences?

When an animal’s body experiences changes in its body pH, many physiological changes occur within the body of the animal. When there is excessive alkalinity in the body and therefore an increase in body pH, this is referred to as alkalosis. Conversely, when there is excessive acidity in the body and therefore a decrease in body pH, this is termed acidosis.

In terms of the effects of pH on the respiration of animals, when lung ventilation is decreased causing CO2

excretion to drop below CO2 production, body CO2 levels rise and pH falls. This is referred to as respiratory acidosis. When lung ventilation is increased


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causing CO2 excretion to rise above CO2

production, body CO2 levels fall and pH rises. This is referred to as respiratory alkalosis.

It is important to know that body fluids are electroneutral, which means that the sum of the anions equals the sum of the cations. Respiratory acidosis and alkalosis disturb the electroneutrality of the body fluids. However, at the cellular levels, the pH is regulated and electroneutrality is brought back to the body fluids. There are various mechanisms, which regulate cellular pH and thus maintain electroneutrality in the body fluids.

One cellular mechanism involves proteins and phosphates within the cell that act as physical buffers to regulate cellular pH. The most important buffers in the blood are proteins, especially hemoglobin, and bicarbonate because the CO2-to-bicarbonate ratio can be adjusted by excretion of CO2 in order to regulate pH.

A second mechanism that regulates cellular pH involves the important reaction of HCO3

- with H+ ions. For example, when oxygen enters red blood cells within the blood, the molecules attach to the hemoglobin thus releasing H+ ions. The pH decreases, which increases cellular acidity and causes the reaction of HCO3

- with H+ ions to form


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CO2. The CO2 then diffuses out of the red blood cells thus regulating the pH within the cells.

Also the proton-exchange and the anion-exchange mechanisms in the cell membrane play important roles in adjusting cellular pH. For example, if a cell is acidified, there is a H+ efflux, which is connected to a Na+ influx and there is a HCO3

- influx, which is connected to Cl- efflux. This mechanism adjusts the pH of the cell to a less acidified state. Lastly, another mechanism for regulating cellular pH involves the simple passive diffusion or active transport of H+ ions from the cells.

What are the organs that facilitate gas exchange/respiration?

Gas transfer occurs by passive diffusion from the environment across the body surface. Air breathing, in most vertebrate animals, involves the movement of air into and out of the lungs. Insects have developed a very different method of gas transfer between the tissues and the environment and this includes a tracheal system. Water breathing, on the other hand, for most aquatic animals involves a unidirectional flow of water over the gills. Thus, the structure and design of the mammalian, insect, and fish respiratory systems are radically different. Each gas-transfer system is


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built according to the needs of the animal and to the medium in which it lives.

In air breathing animals, the related respiratory organ that facilitates gas transfer, is the lung. The lungs in air breathing vertebrates are large organs of respiration located in the chest cavity. In humans, the right lung is made up of three lobes and the left lung is composed of two lobes. They are suspended in the pleural cavity and opens to the outside by the trachea. The respiratory portion of the lung includes the terminal bronchioles (under glossary term as bronchus), the respiratory bronchioles, and the alveolar ducts and sacs.

In contrast, the associated respiratory organs of the fish include the gills. The gills consist of a feathery, branched tissue richly supplied with blood vessels. The gills facilitate the exchange of oxygen and carbon dioxide with the surrounding water.

Most insects respire by means of a tracheal system. In this system, gas is directly transported to the tissues by air-filled tubules that bypass blood. The pores to the outside, called spiracles, deliver the gases of respiration. The drawback of this system is that the gases diffuse slowly in the long narrow tubules; as a result, these tubes need to


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be limited in size for adequate gas transfer. The advantage is that O2 and CO2 diffuse much faster, 10,000 times faster, from the air than in water, blood, or tissues. This feature often uses less energy for ventilation and bypasses the need for a circulatory system. Another advantage of the tracheal system is that oxygen can be delivered directly to tissues that need it, such as flight muscles.

What are the components of the mammalian lung?

The mammalian lung is more complex than that of the amphibian, reptile, or other non-mammal species, and consists of a complex network of tubes and sacs. To be more specific, the human respiratory system consists of the nasal cavity, pharynx, trachea, bronchi, and lungs. Although not considered a part of the respiratory system, the ribs, muscles, and diaphragm are important and help in the expansion and contraction of the lung. To begin with, the pharynx and larynx lead to the lungs; the larynx is connected to the trachea, which branch into the right and left bronchi. These bronchi further divide and lead to the terminal bronchioles. The terminal bronchioles continue and then lead air to the respiratory bronchioles. The respiratory bronchioles themselves connect to a fan of alveolar ducts and sacs. The function of the alveolar ducts


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and sacs is to moisten and cleanse the air taken in, and furthermore, transfer it to the gas-exchanging portion of the lung. These alveolar ducts and sacs are filled with many capillaries, the smallest of the blood vessels, and also consist of connective tissue fibers.

Alveoli, millions of interconnected sacs, also make up a large part of the lung. The human lung is made up of an average of 300 million alveoli. Through diffusion, gases from the air in the alveoli are exchanged with the gases in the pulmonary capillary blood. The transport of gases depends on this exchange and relationship between O2

pressure in the alveoli and the surrounding atmospheric pressure.

As seen, through a series of branches and smaller ducts, air is delivered to the respiratory portion of the lung (the terminal bronchioles, respiratory bronchioles, and the alveolar ducts and sacs); gas is transferred across the respiratory epithelium in these specific areas. Gas transfer also occurs across acini and the pores of Kohn, which allow for collateral (side-by-side) movement of air.

How do different animals ventilate their lungs/spiracles? (mammals, birds, reptiles, frogs, invertebrates)


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The functional anatomy of the lungs and associated structures vary considerably among animals in the mechanism of lung/spiracle ventilation.

Mammals. The lungs of mammals are elastic, multi-chambered bags, which open to the exterior through a single tube, called the trachea. The lungs are suspended within the pleural cavity. The ribs and the diaphragm form the walls of the pleural cavity, which are referred to as the thoracic cage. The thoracic cage mostly consists of the lungs, but between the lungs and the thoracic walls there is a low-volume of pleural space sealed and fluid filled.

During normal breathing, the thoracic cage expands and contracts by a series of skeletal muscles, the diaphragm, and the external and internal intercostal muscles. The respiratory center within the medulla oblongata controls the contractions of these muscles through the activity of motor neurons. During inhalation, the volume of the thorax increases due to the lowering of the diaphragm. In addition, the ribs are raised and moved outward by the contraction of the external intercostal muscles. The increase in thoracic volume reduces alveolar pressure, and air is drawn into the lungs. During exhalation the diaphragm and external intercostal muscles relax, reducing the thoracic volume. Reducing the thoracic volume


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raises alveolar pressure and forces air out of the lungs.

Birds. In the lungs of birds, gas exchange occurs in air capillaries extending from parabronchi, a series of small tube-like structures, which are functionally equivalent to the alveoli in mammals. The parabronchi extend between large dorsobronchi and ventrobronchi, both of which are connected to an even larger tube, the mesobronchus. The parabronchi and connecting tubes form the lung, which is contained within a thoracic cavity. However, the volume of the thoracic cage and lung changes very little during breathing and therefore, are not directly involved in avian lung ventilation. In birds, the air-sac system connected to the lungs ventilates the avian lungs. During inspiration, air flows through the mesobronchus into the caudal air sacs. Air also moves through the dorsobronchus and the parabronchi into the cranial air sacs. Oxygen is then diffused into the air capillaries from the parabronchi and is taken up by the blood. During expiration, air leaving the caudal air sacs passes through the parabronchi and then through the mesobronchus to the trachea. The cranial air sacs, during expiration, move air through the ventrobronchi to the trachea and into the environment. The bird ventilation mechanism is special because birds are capable of flying at high altitudes while maintaining a sufficient


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supply of O2 in their bodies. Specifically, the unidirectional flow of air through the parabronchi aids in increasing the efficiency of gas exchange within the avian lungs thus giving birds the capability of flying at high altitudes. This means of gas exchange is more efficient that thet tidal flow model seen in mammals.

Reptiles. The ribs of reptiles form a thoracic cage around the lungs. During inhalation, the ribs moving cranially and ventrally, enlarging the thoracic cage. This process reduces the pressure within the cage below atmospheric pressure. The nares and glottis open and air flows into the lungs. Exhalation occurs passively by the relaxation of the muscles that enlarge the thoracic cage, which release energy stored in stretching the elastic component of the lung and body wall.

In tortoises and turtles, the ribs are fused to a rigid shell. Outward movements of the limb flanks and/or the ventral part of the shell and by forward movements of the shoulders are what inflate the lungs. The reverse process results in lung deflation, involving the retraction of limbs and head into the shell leading to a decrease in pulmonary volume. Therefore, when a turtle is withdrawn into its shell, its lungs are deflated and the turtle can't breathe.


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Frogs. In frogs, the nares open into a buccal cavity, which is connected through the glottis to a pair of lungs. During inhalation, air is drawn into the buccal cavity with the nares open and the glottis closed. Then the nares close and the glottis is opened. The buccal floor then rises, forcing air from the buccal cavity into the lungs. This lung-filling process may be repeated several times in sequence inhaling air in portions. This same process may also occur during expiration in which the lungs release air in portions. Inhaling and exhaling air in portions may produce a mixture of pulmonary air low in O2 and high in CO2. This complex method of lung ventilation may be to reduce fluctuations in CO2

levels in the lungs to stabilize and regulate blood PCO2 and control blood pH. Frogs also exchange gasses across their skin, so the lungs are not the only repsiratory surface.

Invertebrates. Invertebrates have a variety of gas-transfer mechanisms. In some invertebrates, ventilation does not occur. These invertebrates rely on diffusion of gases between the lung and the environment. Spiders have ventilated lungs called "book lungs". The lungs have respiratory surfaces consisting of thin, blood-filled plates that extend like the leaves of a book into a body cavity guarded by an opening (spiracle). The spiracles open and close to regulate the rate of water loss from these "book


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lungs". Snails and slugs also have ventilated lungs in which their lung volume changes enabling them to emerge from and withdraw into their rigid shells. In aquatic snails the lungs serve to reduce the animal’s density. Most insects have a gas-transfer mechanism called the tracheal system (to know more information on the insect tracheal system, link to the questions: How do insect tracheals work? How are they different from lungs and gills?)

How do gills work?

For most fish species gills work by a unidirectional flow of water over the epithelial surface of the gill, where the transfer of gases is made (O2 in, CO2

out). The reason for this unidirectional flow of water, and not an inhaling and exhaling of water, is due to the energetics of the system. The energy that would be required to move water into and out of a respiratory organ would be much more than that used to move air because water is more dense and viscous.

The blood flowing just under the epithelial gill tissue usually moves in a countercurrent flow to that of the water moving over it. This allows for the most O2 to be taken in by the blood because the diffusion gradient is kept high by the blood picking up oxygen as it moves along, but always coming in contact with water that has a higher O2 content. The


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blood receiving the O2 will continue to pick up O2 as it moves along because fresh water is being washed over the epithelial lining of the gills. An important aspect to remember here is that the water going over the gills needs to be moving unidirectional, either by the fish forcing the water to move in one direction or if the water is moving mostly in one direction.

There are two ways fish ventilate their lungs: buccal/opercular pumping (active ventilation) and ram ventilation (passive ventilation). The fish pulling in water through the mouth (buccal chamber) and pushing it over the gills and out of the opercular chamber (where the gills are housed) accomplishes buccal/opercular ventilation. The pressure in the buccal chamber is kept higher than the pressure in the opercular chamber so the fresh water is constantly being flushed over the gills. A fish swimming with its mouth open, allowing water to wash over the gills accomplishes ram ventilation. This method of ventilation requires fast water or a fast fish to keep enough oxygen going to the gill surface.

How do insect tracheoles work? How are they different from lungs and gills?

Insect tracheal systems are a series of air filled tubes that run from the edge


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of the exoskeleton to the cells/tissues far within the body. The tracheal system terminates at the tracheoles, that often go in between or right into cells to deliver O2 very close to the mitochondria. There is usually fluid between the terminal ends of the tracheols and the body cells, but as the insect becomes more active the fluid is replaced by air so gas exchange is heightened. The use of tracheal systems is superior to using water or blood as mediums of gas exchange because O2 and CO2 diffuse 10,000 times more rapidly in air so the necessary gases can be exchanged more quickly. However, there is a size limit for effective ventilation via a tracheal system, which is one reason that insects cannot grow to gargantuan sizes.

The inner wall surface of the tracheal system is made of the same material that composes the exoskeleton, which helps to prevent water loss. Spiracles, the openings to the outside air, can be opened and closed at will to in regulate air exchange, water loss, and to keep out debris.

Ventilation is usually accomplished through convection, the mass movement of gases. Some larger insects can compress and expand their body wall to coincide with the opening and closing of spiracles to pull air in and push air out. To reduce the amount of energy used in


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respiration some insects use the discontinuous ventilation cycle (DVC) which is composed of open, closed, and intermediate flutter phases. During the closed phase (spiracles closed) the O2

that is in the body is being used more rapidly than the CO2 being produced. Due to this, when the open phase begins there is a O2 gradient, the low end being within the body, forcing a rush of O2

from the surrounding air into the spiracles and releasing any CO2 that was produced. This process may be helped along by the expansion of respiratory sacs within the body to pull more air in or push more air out. During the flutter phase there is rapid inhalation and exhalation. This type of ventilation uses the most energy and it is not understood why it is done.

What is the role of pulmonary surfactants in respiration?

Pulmonary surfactants are lipoprotein complexes produced in the lungs that are used to reduce the effort in breathing and help prevent the collapse of alveoli. Pulmonary surfactants make expansion of the alveoli easier by lowering the surface tension that holds membranes of different alveoli together and minimizes expansion of individual alveoli. This makes it easier for alveoli membranes to slide against each other when they are expanded to take in air.


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Surfactants also reduce the chances of alveolar collapse by stabilizing surface tension when an alveoli sac is expanded. When alveoli are expanded the surfactant is spread out more, which increases surface tension. Surface tension is a major contributor to wall tension, which determines if a small alveolar sac collapses into a larger alveolar sac. Collapse occurs when the pressure inside a small alveolar sac (wall tension in relation to the radius of the sac) is greater that the pressure in a larger alveolar sac, forcing the air in a small sac (high pressure) to force its way into the large sac (low pressure). The surfactant prevents this by minimizing the surface tension, which minimizes the difference in wall tension and thereby minimizing the pressure difference between alveoli.

How are breathing patterns controlled or regulated?

Breathing is an automatic and rhythmic behavior regulated by several nerve centers in the brain, more specifically, in the neurons of the pons and medulla oblongata. The central processing of many sensory inputs control breathing movements. The central processor is made up of a pattern generator and a rhythm generator. From these, the depth and amplitude of each breath is controlled and the frequency of breathing is controlled, respectively.


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Ventilation helps maintain satisfactory rates of gas transfer and blood pH levels. Breathing movements with eating, talking, or other bodily functions are controlled by sensory inputs as well. The muscles and diaphragm help ventilate the lungs. This action is stimulated by the spinal motor neurons and the phrenic nerve that get information from the neurons that make up the medullary respiratory centers. The muscles of the respiratory system are finely controlled, and this allows humans to breathe, sing, and whistle. The medullary respiratory center also contains inspiratory and expiratory neurons. The activity of the inspiratory neurons correspond to inspiration. The networks of neurons connect to higher brain centers, the chemoreceptors and mechanoreceptors.

Neuronal action has much to do with breathing and respiratory activity. From the phrenic nerve or from individual neurons in the medulla, scientists have been able to record inspiratory neuronal activity and learn more. Inspiration is characterized by a changing release of medullary neurons. The activity recorded shows a rapid onset, a gradual rise, and an abrupt termination with a sudden burst of activity related to inhalation. Following this activity, the inspiratory muscles contract and intrapulmonary pressure decreases. Inspiratory neuronal activity can be said to depend on the


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cycle of various neurons- inspiratory, early inspiratory, off-switch, post inspiratory, and expiratory neurons. The "off-switch" neurons come about at the sharp cutoff point in the activity of inhalation, and also when neuronal activity has reached a threshold level. Pulmonary stretch receptors that are stimulated by lung expansion decrease the threshold level. Without these receptors working on the inspiratory neurons, there would be over-expansion of the lung. At the beginning of expiration, the amount of work by the inspiratory muscles begins to decrease, which is caused by the post-inspiratory neurons. The post-inspiratory neurons are responsible for slowing the rates of expiration. At the end of the post-inspiratory activity, the expiratory neurons are then released.

The time between each breath is determined by the interval between the bursts of activity of the inspiratory neurons. The interval between a burst of activity is related to the amount of activity in the burst that came before it, as well as with nerves in the pulmonary stretch receptors. If the activity of inspiration is great, as is when taking a deep breath, there is a longer interval between inspirations. This allows the ratio of duration on inspiratory and expiratory activity to stay constant no matter how long the breath taken is. The pulmonary stretch receptors can influence this ration,


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however, depending on their activity. If these receptors are very active, the duration of expiration may be extended, leaving a longer time for exhalation. This can occur during expiration when the lung empties out slowly and when the pulmonary stretch receptors are still active while the lung stays inflated.

Expiratory neuronal activity appears not to influence normal exhalation. Exhalation most often occurs passively, as the thoracic cavity relaxes after inhalation. Expiratory neurons are used for forced exhalation, however, and are only active when the inspiratory neurons are still.

The human respiratory system has the ability to adjust its breathing patterns to different environments and to disturbances in breathing, such as asthma (a narrowing of the airway which causes breathing difficulties). This flexibility is due to a number of sensors found throughout the body, which send signals to the respiratory networks in the brain. The chemoreceptors detect any changes of acidity that may occur in the cerebral spinal fluid (CSF) in the brain, or in blood. For example, when PCO2 levels increase in the body, the levels of pH in the CSF decrease. The chemoreceptors act to drive ventilation, and the amount of breathing is increased. The mechanoreceptors of the body help maintain any expansions of the lung and


also help maintain the size of the airway.

How does an animal respond to extreme conditions?

Animals have the ability to respond to extreme conditions, such as reduced oxygen levels (hypoxia), increased carbon dioxide levels (hypercapnia), diving, and exercise. As we will see, each of the extremes mentioned will induce a respiratory response specific to its demands.

Decreased O2 levels (hypoxia)

In aquatic environments, gas mixing and diffusion occur less rapidly than in air. Because of this, aquatic animals experience frequent changes in O2 levels and face regions of hypoxia. CO2 levels may or may not come about with different O2 levels.

Some animals can survive periods of hypoxia. To do so, the animals either use anaerobic pathways, or will adjust their respiratory and cardiovascular systems in order to deliver oxygen throughout their bodies while experiencing reduced O2

availability.

In air, the levels of O2 and CO2 can remain relatively stable. There is, however, a decrease in O2 levels with higher altitudes. With increasing


altitude, there is a gradual reduction in PO2, and each animal has a different way of fighting these conditions. For example, and increase in blood levels of 2,3 DPG will decrease the affinity of Hb for O2, thereby releasing more O2 for the tissues to use.

A decrease in PO2 of the air will cause a decrease in blood PO2. The carotid and aortic bodies are stimulated when this happens, causing an increase in lung ventilation. When there is an increase in lung ventilation there is more CO2 eliminated and a reduction in blood PCO2 as well. As a result, the pH of the CSF rises and tends to reduce ventilation. When an animal is in an area of hypoxia for a longer period of time, blood and CSF pH levels are brought back down to normal by the release of bicarbonate in the body. For instance, for a human who has moved to a higher altitude, this process takes about one week. The carotid bodies and the aortic body chemoreceptors may be reset to the lower CO2 levels. Hypoxic conditions cause a vasoconstriction in the pulmonary capillaries and a rise in pulmonary blood pressure. This circulates the blood away from the poorly ventilated areas of the lung.

There are other effects to living in such an extreme condition. Humans, for example, tend to be smaller in size, barrel chested, and have an increased


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lung volume. There is a reduction in limb development and often excessive growth or development of the right ventricle, due to increased pulmonary blood pressures. Also, over long periods of time, most animals will increase the number of red blood cells and the amount of hemoglobin in the blood. This feature increases the oxygen capacity of the blood. If there is a decrease in O2

levels in the blood, erythropoietin, a hormone of the kidney and liver, is produced. This hormone stimultes red blood cells are production in bone marrow. Hypoxia may also result in systemic vasodilation, as well as an increased cardiac output. When O2

supplies are restored from increased hemoglobin levels in the blood and through ventilation, cardiac output is brought back to normal.

Increased CO2 levels (hypercapnia)

PCO2 represents the amount of CO2 in solution. When there is an increase in blood PCO2, there is an increase in ventilation. The aortic and carotid body chemoreceptors, the mechanoreceptors in the lungs, and most especially, the central H+ receptors, regulate this activity. They do so by sending messages to the respiratory center of the brain. The pH of the CSF is brought back to normal levels in order to bring ventilation levels back to normal as well. When there is an increase in CO2


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levels, there is a distinct increase in ventilation. After the stress of increased CO2 levels is relieved, ventilation gradually returns to a level slightly above the ventilation level that occurred before hypercapnia. The reason it returns to a level only slightly above the initial ventilation volume relates to a rise in plasma and CSF bicarbonate levels. As a result of the increased plasma and CSF bicarbonate, pH levels are brought back to normal, even though there may still be a high level of CO2.

Diving by air-breathing animals

During a dive, animals are subjected to periods of hypoxia. Anoxia, severe hypoxic conditions that can result in permanent damage, is a large problem for a mammal’s central nervous system (CNS) and because of this, oxygen must be continuously supplied to the animal. Throughout a dive, animals combat anoxia by making use of oxygen stores in the lungs, blood, and tissues. Animals that dive have higher hemoglobin levels, which increase the oxygen capacity of the blood, and also have larger oxygen stores in muscle ( myoglobin ) to efficiently supply the body with O2. In order to utilize the stores efficiently during a dive, blood is delivered to the brain and heart first. The tissues and organs to where blood did not go to resort to an anaerobic pathway. As a result, the heart rate slows and cardiac output decreases.


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The O2 stores need to be large enough to sustain aerobic metabolism because diving animals cannot tolerate the large buildup of lactic acid from anaerobic metabolism.

During a dive, inspiration is prevented and water is detected from receptors found near the glottis, mouth, or nose. Although there is an increase in CO2 levels and a decrease in blood pH, ventilation is prevented. This is because the carotid and aortic body chemoreceptors are not acted upon by the respiratory neurons to cause ventilation.

One potential danger of a prolonged dive is that gases in solution in the blood under the higher pressure of greater depth may come out of solution too quickly and form air bubbles in the blood vessels when the pressure diminishes. In humans, this can cause a condition known as "the bends", in which gas bubbles accumulate in the joints, and can even obstruct blood flow in small vessels in the brain and other parts of the body. Many diving mammals prevent this condition by exhaling when they dive, thereby emptying most of the air out of their lungs. In addition, under the pressure of diving, the alveoli collapse, thereby forcing air into the bronchioles, where it cannot go into solution in the blood.

Exercise


During exercise, more oxygen is needed, and more CO2 and metabolic acid are produced. In addition, there is an increased cardiac output because the tissues need more oxygen supplied to them. This is also caused due to an increase of lung ventilation to support gas tensions in arterial blood, which experiences faster blood flow. When an individual is exercising, the venous blood shows signs of decreased O2 levels, increased CO2 levels, and an increase in H+ levels. In the arterial blood, however, the average PO2 and PCO2 do not differ much as they do in the venous blood, except when under extreme exercise. When exercise has stopped, there is a decrease in the amount of breathing and eventually, a decline in ventilation volume as well once the balance between O2 consumption and CO2

production is restored and the O2 needs are met. This may take a while, if a significant oxygen debt has been built up by a prolonged period of anaerobic muscle activity.

What are some of the physiological problems associated with high altitude?

Altitude Sickness, and the related disorders and symptoms, pose an immediate threat to athletes who spend their time exercising at high altitudes. The most commonly affected athletes are high altitude mountain climbers. It is not


uncommon to find them above 20,000 feet using skill, strength and concentration to scale some of the most dangerous mountains our Earth has to offer. Unfortunately, the challenge of high altitude mountaineering also brings with it the risk of serious illness and possibly death. Why is this? Why does our body respond so negatively to high altitude environments?

Increased altitude is coupled with decrease atmospheric pressure meaning that for every breath inhaled; there is less O2 available. Think of breathing inside a bedroom filled with 1000 liters of O2. There is plenty of air around you and the pressure is high, like it is at sea level. Now imagine you are breathing in a warehouse that is filled with an equal amount of air. The decreased in pressure would make it harder to breathe. The atmospheric pressure on top of Mt. Everest (29,028 ft) is 33% less than it is at sea level. This means that 66% less oxygen is available. This is what climbers face when performing at high altitudes.

Due to the oxygen constraint, our bodies are forced to work harder to continue to metabolize. Respiration must increase to get sufficient oxygen across the lungs. Increasing our respiration can be taxing to our systems. If the body overdoes it, Acute Mountain Sickness (AMS) can occur. This is the result of


increased respiration and circulation. The body overcompensates for the decreased oxygen by sending too much to the brain. Leakage into the brain occurs and causes swelling. Decreased oxygen also starves nerve cells, triggering the release of adenosine. This chemical decreases the body’s metabolism, decreasing our need for oxygen. It also dilates blood vessels into the head and neck, which allows more oxygen to go to the brain. This is the same dilation that is correlated with migraine headaches. A common treatment for the migraine symptoms is the use of caffeine.

Caffeine blocks the adenosine receptors, thus preventing vasodilatation. If AMS goes unnoticed, a more serious sickness can occur. High Altitude Cerebral Edema (HACE) has occurred from 10,000 ft. and above. It occurs when AMS is overlooked and thus brain swelling increases. In extreme cases, death can result. The symptoms of HACE are imbalance, severe headache, vomiting, nausea, and hallucinations. Known treatments include rapid descent, supplemental oxygen, water, and a diuretic called Diamox.

Victims of HACE often experience comas and death. The increased blood flow, as a result of high altitude that was mentioned before, can also lead to High Altitude Pulmonary Edema (HAPE). This occurs when excessive blood pressure


causes fluid to leak from the blood vessels into the alveoli sacs of the lungs. Cases have been seen at 8,000 ft. and above and were characterized by difficulty breathing, gurgling sound in lungs, fever, coughing, and exhaustion. The fluid in the lungs blocks the oxygen-blood interface. The body compensates by increasing heart rate and blood pressure, thereby forcing more fluid into the lungs. Eventually, if altitude is not decreased, the victim drowns. No oxygen reaches the lung/capillary interface.

Other problems associated with high altitude include Periodic Breathing and Khumbu Cough. In Periodic Breathing, during sleep above 14,000 ft., climbers will repeatedly stop breathing, gasp, hyperventilate, and then stop again. The medulla of the brain is affected causing breathing to become irregular. CO2 builds up, the sleeper hyperventilates, CO2

decrease, respiration stops, and the cycle continues. The body actually responds to a state of alkalosis, which causes the shut off of breathing. Khumbu Cough is commonly seen with high altitude climbing. It is characterized by a dry cough that results from too high a breathing rate. The mucosa of the bronchi dries out due to the increased breathing rate and contact with dry, cold air. Besides irritation, the Khumbu Cough can result in broken ribs as a result of severe coughing episodes. The only prevention is to keep the breathing rate


down. This reduces the drying out of the mucosa.


Circulatory System

Transport systems functionally connect body cells with the organs of exchange

The exchange of oxygen, carbon dioxide, nutrients and metabolic waste between an organism's cells and the environment occurs across fluid-bathed membranes. Because most of their cells are to far from the outside environment to be serviced by diffusion or active transport many animals have a special system that transports chemicals within the body by transporting fluids ( blood or interstitial flidy0 through out the body, transport systems provide a lifeline between the aqueous environment of living cells and the organs such as the lungs, the exchange chemicals with the outside environment.

The transport system also functions in homeostasis enabling other organ systems to regulate the chemical and physical properties of the cellular environment.

Most invertebrates have a gastrovascular cavity or a circulatory system for internal transport

Cnidarians and flatworms have gastrovascular cavities that function in circulation as well as digestion.

Arthropods and most mollusks have Notes in Animal Physiology by CCDivina………… 111

open circulatory systems, in which tissues are bathed directly in hemolymph pumped by a heart into sinuses. Annelids and some mollusk have closed circulatory systems with blood confined to vessels, some of which pulsate and function s hearts.

Diverse adaptations of a cardiovascular system have evolved in vertebrates

In vertebrates, blood flows in a closed cardiovascular system consisting of blood vessels and a two-to four- chambered heart, the heart has one atrium or two atria. Which pump blood into arteries. Arteries branch into arterial exchange between blood and interstitial fluid. Capillaries rejoin into venules that converge into veins.

In fishes, the heart has a single atrium and single ventricle that pump blood to gills for oxygenation the blood then travels to other capillary beds of the body before returning to the hear.

Amphibians and most reptiles have a three-chambered heart in which the single-ventricle pumps blood to both lungs and body in the pulmonary and systemic circuits. These two circuits return blood to separate atria. Their soluble circulation repumps blood returning from the capillary beds of the respiratory organ, thus ensuring a strong flow of blood to the rest of the body.


Birds and mammals, both endotherms, have four chambered hearts that keep oxygen-rich and oxygen-poor blood completely separated.

Rhythmic pumping of them mammalian heart drive blood through pulmonary and systemic circuits.

The Heart

The cardiac cycle consist of periods of contraction, called systole and periods of relaxation called diastole.

Heart valves dictate a one-way flow of blood through the heart

Together with the stroke volume, heart rate ( pulse) determines cardiac output the volume of blood pumped into the systemic circulation per minute.

The intrinsic contraction of the cardiac muscle is coordinated by a conduction system originating in the sino-atrial (SA node ( pacemaker0 of the right atrium, the pacemaker initiates waves of contraction that spreads to both atria, hesitates momentarily at the atrioventricular (AV) node and then progresses to both ventricles. The pacemaker is in itself influenced by nerves,


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hormones and body temperature and by atrial volume changes during exercise.

All blood vessels including capillaries, are lined by a single layer of endothelium, arteries and veins have to additional outer layers composed of characteristic proportions of smooth muscle, elastic fibers and connective tissue.

The velocity of blood flow varies in he circulatory system being slowest in the capillary beds as a result of the high resistance and large total cross-sectional area of the arterioles and capillaries, this slower flow enhances the exchange of substances between the blood and interstitial fluid.

Blood pressure is determined by cardiac output and peripheral resistance due to variable constriction the arterioles.

Muscular activity and pressure changes during breathing propel blood back to the heart in veins equipped with one-way valves.

The steady supple of blood to different organs is determined by variable constriction of arterioles and capillary sphincters.


Capillary exchange is the ultimate function of the circulatory system substances transverse the endothelium in endocytotic-exocytotic vesicles, by diffusion or are dissolved in fluids force out by blood pressure are the arterial ends of the capillary.

HEART- pulsatile, four–chamber pump composed of two atria and two ventricles; Atria principal entryway to the ventricles; Ventricles supply main force that propels blood throughout the lungs and through the peripheral circulatory system

Physiology of Cardiac Muscle3 muscles – (1) atrial muscle , (2)

ventricular muscle and (3) specialized excitatory and conductive muscle fibers

atrial and ventricular type contract

same as skeletal muscle fibers Excitatory muscle - provide

excitatory system and transmission system for rapid conduction of impulses throughout the heart

Cardiac muscle as a functional

syncitium, intercalated discs – membranes that separate individual cardiac muscle cells flow with relative ease along the axes of the cardiac muscle fibers so that action potentials travel from past the


intercalated disc without hindrance - in syncitium

2 syncitia – atrial and ventricular

syncitiaConductive sytem A-V bundle

conductive system for both atria and ventricle

All or Nothing Principle Applied to the Heart

Stimulation of any single atrial muscle fiber causes the action potential to travel over the entire muscles mass

Role of Calcium

Action potential travels over the muscle fiber membrane causing action potential to travel into the interior of the fiber through T tubules. T tubules causes the calcium ions to be released into the muscle fiber sarcoplasm from the cisternae of the sarcoplasmic retiluculum. Ca ions diffuse rapidly onto myofibrils and chemical reaction promote the sliding of the actin and myosin filaments along each other- muscle contraction.

Immediately after the calcium ions are transported back into the sarcoplasmic reticulum or into the t tubules -muscle relaxes.


The Cardiac Cycle

period from one end of heart contraction to the end of the next is the cardiac cycle

each cycle is initiated by spontaneous generation of an action potential in the S-A node. located in the posterior wall of the right atrium near the opening of the superior vena cava and the action potential travels rapidly through both atria and thence through the A-V bundle, onto the ventricles

The atria acts as primer pump for the ventricle, and ventricle provide the major source of power for moving blood through the vascular system

Systole and Diastole. Diastole period of relaxation Systole – period of contraction.

Functions of the Valves

The Atrioventricular Valves. A-V valves (tricuspid and mitral

valves) prevent backflow of blood from the ventricle to the atria and seminal valve (aortic and pulmonary valves ) prevent backflow from the aorta and pulmonary arteries into the ventricle during diastole. The valves closes when a backward

pressure gradient pushes blood backward and they open when a forward pressure


gradient forces blood in the forward direction .Papillary muscles attach to the vanes

of the A-V valves by the chordae tendineae. Papillary muscles contract when the ventricular walls contract, the pull the vanes of the valves inward toward the ventricle to prevent the bulging too far backward toward the atria during ventricular contraction Aortic and pulmonary valves. The high

pressures in the arteries at the end of systole caused the seminar valves to snap to the close position in comparison with a much sought closure of the A-V valves. The velocity of blood passing through

the aortic and pulmonary valves is far grater than the through the AV valves

Regulation of Cardiac Function

When at rest, the heart pumps only 4 to 6 liters of blood each minute, however during severe exercise it may be required to pump as much as 5x this amount Two ways of regulation:

1. Intrinsic auto regulation in response to changes in volume of blood flowing into the heart

2. Reflex control of the heart by the autonomic nervous system.

Intrinsic auto regulation of cardiac pumping –

Frank Starling Law of the heart


The greater the heart is filled during diastole, the greater will be the quantity of blood pumped into the aorta within physiological limits, the heart pumps all the blood that comes to it without allowing extensive damming of blood in the veins.

When cardiac muscle becomes stretched in an extra amount, when extra amount of blood enters the heart chamber, the unusually stretched muscle contracts with a greatly increased force, thereby automatically pumping the extra blood into the arteries

Control by Nerves

The nerves 1. Change the heart rate 2. Change the strength of

contraction of the heart and 3. Parasympathetic stimulation

decreases heart rate and sympathetic stimulation increases heart

Some Factors Affecting Rate of Heart Beat1. Exercise. Exercise over a period of

many weeks lead to hypertrophy of the cardiac muscles and enlargement of the ventricular chambers – enhanced strength of heart

2. Excess potassium ions in extracellular fluid causes the heart to become extremely dilated and flaccid and slow the heart rate. Very large quantities


can block conduction of the cardiac impulse from the atria to ventricles through the A-V bundle – weaker contraction

3. Excess calcium ions causes effect almost exactly opposite to potassium – spastic action

4. Sodium ions decreases cardiac function similar to potassium. sodium ions compete with calcium ions

Rhytmic excitation of the heart

The heart is endowed with special system for generating rhythmical impulses to cause rhythmical contraction of the heart muscle and for conducting these impulses throughout the heart. The adult human heart normally contracts at 72 beats per minute.

Special excitatory conductive systems of the heart that control cardiac contractions

1. S-A node, normal rhythmic self-excitatory impulse is generated

2. A-V node, in which the impulse from the atria is delayed before passing into the ventricles

3. The A-V bundle, which conducts impulse from heart atria into the ventricles

4. The left and right bundles of Purkinje fibers- conduct cardiac impulse to all parts of the ventricles.


SA NODE

Small crescent shape strip of specialized muscle in posterior wall of the right atrium immediately beneath median opening of the superior vena cavaS-A node controls the rate of heat beat

of the entire heartThe membranes of the S-A fibers are

very permeable to sodium, therefore, large numbers of sodium ions leak to the interior of the fiber, causing the resting membrane potential to drift continually towards a more positive value. Just as soon as the membrane potential reaches threshold level for discharge, an action potential occurs. At the end of the action potential, the membrane become highly permeable to potassium ions and leakage of potassium ions out of the fiber carries positive charges outside, therefore, the inside membrane potential now become more negative than ever because of loss of positive charge causing hyperpolarization. This condition persist for a fraction of a second and then disappears when the natural leakiness of the membrane to sodium ions elicits another action potential.

Arteries , Veins and Capillaries

The rate of blood flow in any spot in circulatory systems depends on the total cross-sectional area of the vessels.


The aorta and venae cavae have smaller cross sectional area in the comprasion to the arterioles, capillaries and venules added together. The rate of blood flow is therefore

faster in the aorta and venae cavae and slowest in the capillaries. As blood leaves the capillaries and

passes into veins, the total cross-sectional area through which it flows is reduced, so that rate of blood flow accelerates even the blood pressure remains loss.

Regulation of Blood flow through the Vessels

The amount of blood flowing into a given capillary bed or into the veins is also under the direct control of nervous systemsVasoconstriciton – contraction of the

precapillary sphincters and the walls of the vessels in response to nerve impulses Vasoconstriction helps stabilize blood

flow during a change in body position such as standing up after lying in bed. Capillaries open in response to local

tissue needs. The opening is vasodilation

Blood is a connective tissue with cells suspended in plasma.


Whole blood consist so of cellular elements (cells and pieces of cells 0 suspended in a liquid matrix called plasma. Plasma is a complex aqueous solution of inorganic electrolytes, proteins, nutrients, metabolic waste products, respiratory gases and hormones. Plasma proteins, influence blood pH , osmotic pressure, and viscosity, and function in lipid transport, immunity ( antibodies and blood clotting ( fibrinogens). Red blood cells or erythrocyte transport oxygen a function reflected in their small size, biconcave shape, anaerobic metabolism and hemoglobin content. Pluripotent stem cells in the red bone marrow give rise to all type of blood cells.

Erthyrocytes (RBC) A. General points

1. Life span of 120-130 daysNotes in Animal Physiology by CCDivina………… 123

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2. Number present: Male: 5 x 106/mm3 Female: 4.5 x 106/mm3

3. RBCs are 500-1000 times more numerous than leukocytes B. Morphological features

1. Biconcave disk with a diameter of 7-8 um and width of 2 um. The shape is dependent on the spectrin-ankyrin-actin interaction.

2. Lacks a nucleus in mammals, but nucleated in other forms (birds, etc.)

3. Lacks a Golgi, centrioles, lysosomes, RER

4. Very few or no mitochondria , resulting in anaerobic glycolysis and pentose phosphate pathways being important for energy production.

5. Cytoplasm composed of: a. water - 65% b. organelles

- 1% c. hemoglobin - 34% C. Function : transport of O2 and CO2

Five types of white blood cells or leucocytes, function in defense by phagocytosis of bacteria and debris or by producing antibodies.

Leukocytes (WBCs)

A. Involved in both the cellular and

humoral defenses of the organism.

B. Morphological features


1. Granulocytes/polymorphonuclear a. have specific granules in the cytoplasmb. non-mitotic cells in the blood stream and after leaving the vascular systemc. three types: neutrophils, eosinophils basophils

2. Agranulocytes/mononuclear a. lack specific granules in the

cytoplasmb. differ from granulocytes in that

they can reproduce by mitosis after leaving the vascular system

c. two types: lymphocytes and monocytes

1 . Neutrophils (Polymorphonuclear neutrophils, polys, PMNs, polymorphs)

A. General points 1.

Characterized by many lobed nucleus and specific granules in cytoplasm2. Comprise 50-70% of differential count3. 4,400/mm3

B. Morphological features 1. Diameter of 10 to 15 um


2. Nucleus generally segmented, consisting of 2 to 5 lobes held together by chromatin; young or immature cells are non-segmented (band or stab); may comprise 1% of cells

3. Cytoplasm - very little RER, Golgi, free ribosomes, and few mitochondria ; three types of granules (formed by the Golgi apparatus): 50-200 granules/cellC. Functions

1. Neutrophils serve as a first line of cellular defense against invasion of microorganisms. PMNs are chemotactically attracted by devitalized tissue, bacteria, and other foreign bodies and factors produced by antigen- antibody interactions with certain blood proteins (complement) and they migrate to the site of infection

2. Killing of bacteria is thus accomplished via two different mechanisms:

a. enzymatic (via fusion of specific and azurophilic granule contents with the phagosome) which involves:

(1)phagocytosis of the foreign material, thus forming a phagosome,

(2) the specific granules fusing with the phagosome, inactivating the material,

(3)the azurophilic granules fusing with the phagosome, digesting the material, and

(4)finally the digested material expelled from the cell.


b. via formation of reactive oxygen compounds within the phagosome

3. Neutrophils die and become the pus of an abscess.

4. Not all bacteria destroyed by neutrophils. For example, the tubercle bacillus survives phagocytosis by the PMN, and must be contained by the macrophage which is derived from the monocyte

Eosinophil (polymorphonuclear eosinophil)

A. General points 1. Characterized by its large

eosinophilic granules in the cytoplasm

2. Comprise 1-4% of the differential count

3. 200/mm3 B. Morphological features

1. Diameter of 12 to 17 um2. Nucleus generally consists of two

lobes held together by a strand of chromatin; more than two lobes is not common Cytoplasm has lysosomes and contain

hydrolytic enzymes and peroxidase; contents help in the destruction of parasitic worms and in the hydrolysis of antigen-antibody complexes internalized by the eosinophils

C. Functions


1. Eosinophils leave the vascular system by diapedesis, and locate especially in the connective tissue beneath the epithelium of the respiratory and gastro-intestinal tract.

a. binding of histamine, leukotrienes, and esoinophil chemotactic factor (released by mast cells, basophils, and neutrophils) to eosinophil plasma membrane receptors results in the migration of the eosinophils to the site of the allergic reaction, inflammatory reaction, or parasitic worm invasion

2. The differential count of eosinophils increases with parasitic infections (trichinosis, schistosomiasis, ascaris)

a. major basic protein and eosinophil cationic protein bore holes in the pellicles of parasitic worms, facilitating access of reactive oxygen compounds (e.g. superoxides; hydrogen peroxide) to the parasite

3. Differential count increases in allergic conditions such as hay fever and asthma.

4. Cells play a role in the phagocytosis and hydrolysis of antigen-antibody complexes.

5. Eosinophils degrade chemical mediators such as leukotrienes


and histamine released by mast cells and basophils, thus regulating local inflammatory responses

Basophil (Polymorphonuclear basophil)

A. General points 1. Comprise about 0.5% of

differential count2. 40/mm3

B. Morphological features 1. Diameter of 8 to 12 um2. Nucleus ; irregular shape, does

not appear to be lobated C. Functions

1. Increase in number along with other leukocytes with leukemia.

2. Increase in number in smallpox, chicken pox, and sinus inflammations.

3. Functions are appear to be involved in mediating allergic and inflammatory reactions (functions are similar to mast cells)

a. antigens can bind to IgE molecules whose Fc portion is bound to Fc receptors on the basophil surface; this may cause the basophils to release the specific granule contents into the extracellular spaces

(1) release of histamine causes smooth muscle contraction (in the bronchial tree), vasodilation of the microvasculature, and leaking of blood vessels


b. begin to produce and release leukotrienes

(1) similar effects to histamine, but actions are slower and more persistent

4. Lymphocytes A. General points

1. Produced in lymphatic nodules, lymph nodes, spleen, thymus, tonsils, and bone marrow, and endow the body with its immunological defense.

2. Comprise 20-40% of differential count

3. 2,500/mm3

B.Subdivision of small lymphocytes based on their function, not on morphologic features. 1. B-lymphocytes

a. compose about 15% of circulating lymphocytes

b. called B-cells because in chick develop in bursa of Fabricius

c. in humans develop in bursa equivalent (gut) or bone marrow

d. cells may leave the circulation and enter lymphatic tissue where by the process of mitosis they give rise to clones of B-cells

e. function or fate of B-lymphocytes: (1)Plasma cells - produce antigen-

specific circulating immunoglobins (humoral antibody response)


(2) Memory cells - found in lymphatic tissue and stimulated by re-exposure to antigen; reaction termed the secondary response

2. T-lymphocytes a. compose 80-90% of circulating

lymphocytesb. originate embryological from the

yolk sac and seed the thymus by way of the liver and bone marrow

c. multiply and differentiate into T-lymphocytes in the thymus - each developing lymphocyte develops an individual antigenic specificity.

d. activation of T-cells (needed for activation)

(1) appropriate antigen(2) macrophages must process the

antigen for presentatione. subsets of T-lymphocytes

(1) Cytotoxic T cells(2) T helper cells(3) T suppressor cells

f. function of T-lymphocytes : cell mediated immunity; assist in humoral immunity

5. Monocyte A. General points

1. Characterized partly by its large size

2. Comprise 2-8% of the differential count

4. 300/mm3


5. Cells originate in the bone marrow B. Morphological features

1. Diameter of 12 to 20 um2. Nucleus a. eccentrically placed and may be

oval, indented, kidney or horseshoe shaped

b. chromatin less condensed than in lymphocyte, and therefore, nucleus in lighter staining

C. Functions 1. Monocytes exhibit diapedesis

(continually extend and withdraw pseudopodia) and reach full development outside the blood stream where they are known as macrophages. Macrophages fuse to form foreign body giant cells and osteoclasts; In the CNS the macrophages form microglia; in the liver, Kupffer cells; and in the lungs, alveolar macrophages.

2. Serve as the second line of defense against invading organisms. Found in areas of chronic inflammation.

3. After leaving the vascular system, the macrophage (monocyte) plays a role along with the T-lymphocyte in the differentiation of the B-lymphocyte into the plasma cell, which produces immunoglobulins.

4. Some macrophages are particularly good at processing and presenting antigen and are called antigen presenting cells

5. Monocytosis - increased monocyte count due to infectious and


inflammatory diseases, tuberculosis, and leukemia.

Platelets

Platelets are fragments of cells produced in the bone marrow that function blood clotting , a cascade of complex reactions that converted the plasma fibrinogen to fibrin.

1. Thrombocytopenia - a deficiency in platelets (<60,000/mm3). May occur with certain viral diseases.2. Role in clot formation:

a. With trauma, platelets release seratonin which causes contraction of vascular smooth muscle, reducing blood loss.

b. When vessel ruptures, platelets agglutinate, forming a plug which helps close the gap

c. Platelets release the enzyme thromboplastin

3. Functions in the maintenance of endothelial cells - with thrombocytopenia, blood vessels loose their competence and blood seeps out into the tissue, resulting in the condition of thrombocytopenia purpura.

Cardiovascular disease are the leading cause of death

A leading cause of death is cardiovascular disease, a deterioration


of the heart and blood vessels. Gradually plaque build up during artherosclerosis or arteriosclerosis narrows the diameter of blood vessel and may be associated with vessel blockage and consequent heart attack of stroke.

Commonly Asked Questions

What are the advantages of a closed, as compared with an open, circulatory system?

Two basic types of transport systems – the open and the closed circulatory systems- occur in the larger invertebrate animals. Smaller animal do not need transport systems, for all of their body cells are near internal cavities or the external environ, In an open circulatory system, the blood is not completely enclosed with the vessels, the hearts pump blood through arteries into large cavities or sinuses, where it mixes wit interstitial fluid and bathes the cells of the body. The blood is slowly return to the heart through small pores, called ostia. And bathes the cell of the body. The blood is slowly returned to the heart s through small pores called ostia. In a closed circulatory system, the blood remain within a completely enclose system o f vessel and never comes in a direct contact with the body cells Material move between the blood and interstitial fluid through the thin walls of capillaries.


Circulation is slower in an open system, because with some of the blood pooled in sinuses, the hearts cannot build up enough pressure to make the blood flow rapidly. In an open system cannot achieve high rates of oxygen transport that active animals requires animals with open system are either quite small and sluggish of use the open system only for transport of food and wastes and use a different system for transport of gases. Insects for opens system only transport of food and wastes and use a different system for transport of gases, Insects of example, have a separate system of vessels- the tracheal system – for gas transport, the insects circulatory system is composed of five muscular hearts which slowly pump the blood, which contains food and wastes (except carbon dioxide, hominess and other material though a system of vessels and open cavities in a forward and downward direction. the blood bathes the cells of he body in open cavities below the vessel. Providing the necessary materials (except oxygen) for cellular activities and accumulating waste products 8 except carbon dioxide from the cells. The blood then moves slowly form these cavities backward and upward to the hearts. Transport is accelerated during physical activity, when the skeletal l muscles contact rhythmically, squeeze the cavities and forcing the blood back toward the hearts.


Invertebrate animals that have open circulatory systems include the arthropod (such as insects, spiders, crabs and lobsters, and most mollusks (such as snails, oysters and clams. Invertebrates with a closed circulatory system include the annelids such as earthworms and some mollusks (such as squids).

How can a frog or a lizard be very active if its oxygen-rich blood mixes with oxygen-poor blood before becoming available to the body cells?

A frog or a lizard has a single ventricle, which receives oxygen-poor oxygen –poor blood from the body as well as oxygen-rich blood form the lungs, and in the case of a frog, from the skin. Blood from the ventricle is pumped via one artery to the lungs (and skin, in the case of a frog) and via another artery to the rest of the body. In neither animal, however, is there’s complete mixing of the two types of blood in the ventricle, a frog has ridge of hear tissue hat partially segregates the ventricle into a left and right side. The ridge divert unoxygenated blood fro the right atrium to he artery leading t the lungs and skin and oxygenated blood from the left atrium to the artery leading to the rest of the body. A lizard has septum, or wall, in its ventricle that perform the same function, but perform it much better that


the ridge in frog’s ventricle. The septum almost completely separates the ventricle into a left and right side there is a very; little mixing of oxygenated and unoxygenated blood in a lizard heart. The active cells of both a frog and a lizard receive highly oxygenated ventricles. A bird or mamma, however, has a greater need for oxygen, because of the high metabolic demands of endothermy,

What controls heart rate?

The rate at which the heart muscles contract is regulated in several ways, the main controls is the sino-atrial node or pacemaker, which’s a small piece of specialized hat muscle located in the wall of the right atrium. Electrical impulses emitted at regular interval by this tissue stimulate muscle contraction the four chambers of the heart. Each impulse travels through both atria, causing them to contract almost simultaneously, and on to another specialized region – the atrio-ventricular node – which transmits the impulse to both ventricles simultaneously, the slight delay in the signal produces a sequence of contrition first the two aria, the then two ventricle.

A second regulator of heart rate is an area within the medulla oblongata of the rain. The cardio-inhibitory center in


this area communicates with the Sino trial node via the vagus nerves, which contain both afferent and efferent axons. The afferent nerve axons, which originate in the node and terminate in the cardio-inhibitory center and extend to the sinoatrial node, can time the node to decrease the rate of heart-muscle contractions. The cardio-inhibitory center functions to restrains the Sino Arial node, to hold the heart rate in check.

In addition to feedback from the sinoatrial mode, the cardio-inhibitory center receiver information from sensory surfaces and higher brain centers. Sensory cells on the internal and external body surfaces transmit information t the center about such conditions as indigestion, inhalation of irritating fumes sudden cold temperatures and blood pressure, when the center receiver the information, it stimulates the efferent axons of the vagus nerves, which diminish the heart rate certain emotional l state also stimulate the cardio-inhibitory centers, many areas of the brain are involved in the regulation of emotion, but the critical pathway that influences heat rate form the limbic system to the cardio-inhibitory center.

The cardio-accelerating with the medulla oblongata of the brain is stimulated by many factors; including the pain sensations form the skin and


anticipation of exercise. Efferent neurons form the cardio-accelerating center terminate in the heart muscle themselves, rather than in the sinotarial node. When the stimulated, these neurons release a neurotransmitter (norephineprine) that increase both the heart rate and the stroke volume (amount of blood pumped with each contraction

Hormones also affect the heart rate. Thyroxin, the hormone secreted by thyroid gland, increases the heart rate, Epinephrine. A hormone secreted by the adrenal medullas, increases both the rate and the stroke volume.

What regulates the rate a blood flows though the circulatory system.

Animals must be able to adjust the rate of blood flown in response to changing conditions when cellular activity is low, as during sleep, the ea of blood flow is lowered to conserve energy. During strenuous activity, the rate of blood flow must b e rapid enough to meet the increased demand for exchange of material between the bloods and more active cells.

The cardiac output, or quantity of blood the heart pumps per minute, is about 5-liter sin a resting human. Cardiac outputs is the product of two factors, - the heart rate (number of


contractions per minute) and Stroke volume (amount of blood ejected from the heart during each contraction)

Heart rate is controlled primarily by Sino Arial node, but also by cardio-inhibitory and cardio-accelerating center within the medulla oblongata of the brain and by hormones secreted by the thyroid and adrenal glands.

Stroke volume is controlled by artery diameter. Because the vessels and the heart form a closed circulatory system, net volume of blood expelled form the heart during each contraction can only be increase if the rate at which blood is returned to the heart undergoes a corresponding increase. As the volume of blood returning per minute to the heart increases, the muscles conditions that force blood through the heart becomes stronger. Blood is returned other heart more rapidly when the blood pressure is higher i.e. when arteries are more constricted.

Artery diameter is controlled by vasomotor center in the medulla oblongata in response to carbon dioxide levels in the blood and by brain centers that control emotions Higher concentrations of carbon dioxide, a waste product of cellular respiration, reflect high levels of cellular activity, the amount of carbon dioxide in the blood detected by neurons in two vasomotor center, one on


each side of the medulla oblongata, which send electrical-chemical impulses along vasomotor nerves to the muscles of the arties. High levels of carbon dioxide cause constriction of the arterial walls, and thus and increase in blood pressure and amore rapid flow of blood thorough the circulatory system. Low levels of carbon dioxide product the opposite effect: the arteries become dilated blood pressure drops, and blood flow becomes slower.

Finally blood flow is controlled by the brain center that control the emotions, including the cerebral cortex in the limbic system, which emits electrochemical impulses that travel to the vasomotor center of ht medulla oblongata, Certain emotional states can accelerate the heart rate and constrict the arteries, other emotion stress can inhibit the heart rate and dilate the arteries to though the point that the individual faints, Information is I transmitted from the vasomotor center to the arterial walls, which either constricts of dilates vessels.

Applications

1. The ECGAs the heart goes through its

contraction-relaxation cycle, waves of depolarization and repolarization pass from the atria to the ventricular tissue. These waves produce a measurable


electrical current and associated voltage changes. Since alterations in heart function due to disease are often reflected units electrical activity patterns, analysis of the patterns has considerable diagnostic use.

The instrument used to measure heart electrical activity is called an electrocardiogram, where electrodes are attached to the body. These lead to an amplifier where the tiny voltages are magnified and fed into a recorder. An example of a normal tracing is shown in the figure. There are five distinct alterations in voltage, called P,Q,R,S and T for reference. Notice that the measured voltages are very small, approximately a thousandth of a volt. In the heart the voltage changes are nearly a hundred times larger, but the electrocardiograph can only measure the voltages that reach the surface of the body.

The first small change, the P wave is produced when the atria depolarize, the depolarization wave travels to the ventricle where a much larger change occurs, called the QRS region. The final T wave is produced by the repolarization of the ventricles. Now, compare the normal tracing with the one made form a fibrillating heart. Fibrillation occurs when the heart muscle contractions are irregular and uncoordinated and often sets in after a severe heart attack. In


fact, fibrillation is the usual cause of death. The ECG clearly shows the random patterns associated with the fibrillating heart. Of course, this is an extreme case, the ECG is more often used to diagnose heart disease sickness subtle changes in the ECG pattern can be related to specific kinds of heart damage form disease.

An example of such an abnormal patter in is called an atrioventricular block and results when the tissue that normally conducts the electrical waves from the atria to the ventricles is damaged by disease to the extent that conduction is impaired. In a block leak, there is no coordination of contraction between atrial and ventricles and the heart’s efficiency as a pump is greatly impaired.

The Pacemaker

Artificial pacemakers. As we age, the heart may lose control of its beat, the most common cause of this condition is that conduction between the atria and ventricles is blocked. The atrium may contract normally at 70 to 80 times per minute, driven by the pacemaker tissue, but the ventricles beat at their own rate at 40 to 50 times per minute.

In many instances, it is possible to implant an artificial pacemaker near the heart. this is a device that delivers a


small electrical shock to the heart at timed intervals, the purpose of the shock is not so much to initiate heart beat as to coordinate the atrial and ventricular contractions. For instance, the pacemaker can be set so that it produces ventricular contractions. For instance, the pacemaker can be set so that it produces a ventricular contraction whenever the atria contract.

A relates application of our knowledge is the defibrillator, now found in most hospitals, during fibrillation, waves of contraction are moving randomly in heart muscle and the problem is to coordinate them. The defibrillator does this by sending a single strong electrical shock through the chest wall into the heart. the heart muscle responds by contracting completely, then often begins to beat normally under the influenced of its pacemaker tissue.

Sphygmomanometers.

Blood pressure is an important indicator of vascular function and most of us have had our blood pressure measures. The instrument is called a sphygmomanometer, and consists of an inflatable cuff that is calibrated so that a air pressure in the cuff reads out in millimeters of mercury to operate the devise, the cuff is wrapped around the upper arm while a stethoscope is placed at the inner elbow near the artery that


supplied blood to the heart. As the cuff is inflated, the blood pressure in the artery is overcome so that the artery collapses. Pressure through the artery in spurts. At this point , a thumping is heard in the stethoscope as the artery fills and collapses this is a good estimate of systolic blood pressure. More pressure is then released and at a second point the thumping sound disappears when the artery stays open even during diastole. This pressure is equivalent to the diastolic blood pressure.


THE EXCRETORY SYSTEM

Cells produce water and carbon dioxide as by-products of metabolic breakdown of sugars, fats, and proteins. Chemical groups such as nitrogen, sulfur, and phosphorous must be stripped, from the large molecules to which they were formerly attached, as part of preparing them for energy conversion. The continuous production of metabolic wastes establishes a steep concentration gradient across the plasma membrane, causing wastes to diffuse out of cells and into the extracellular fluid.

Single-celled organisms have most of

their wastes diffuse out into the outside environment. Multicellular organisms, and animals in particular, must have a specialized organ system to concentrate and remove wastes from the interstitial fluid into the blood capillaries and eventually deposit that material at a collection point for removal entirely from the body.

As animals perform their various metabolic processes, protein and nucleic acid, both of which contain nitrogen, are broken down. While some of the nitrogen is used to manufacture new nitrogen-containing molecules, much of it cannot be used for this purpose and must be disposed of as waste. Typically, the first nitrogen-containing molecule that forms is ammonia (NH3, which is very Notes in Animal Physiology by CCDivina………… 146

http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookglossC.html#capillaries

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water-soluble, forming NH4OH, a strong base. In some way, this ammonia must be gotten rid of before it raises the pH of the body fluids. Because ammonia is so water-soluble, aquatic animals often can get rid of it just by diffusion into the surrounding water. However, ammonia doesn’t readily go from body fluids into air, so terrestrial animals need other ways of getting rid of nitrogenous wastes.

The two most common substances used by terrestrial animals to get rid of excess nitrogen are urea and uric acid. Many animal species that aren’t terribly concerned about water-loss, including humans, convert the ammonia to urea, which is water-soluble and excreted in a water-based solution. Other organisms such as birds, insects, or lizards, especially if they live in an arid area, must conserve water whenever possible, thus convert the NH3 to uric acid. Uric acid is not water-soluble, thus can be excreted with little, if any, water with it. This is the white goo in bird droppings. While the major portion of human nitrogenous waste is in the form of urea, humans typically excrete some uric acid, too. Uric acid is another kind of purine like the adenine and guanine in our DNA

Regulation of Extracellular Fluids


Excretory systems regulate the chemical composition of body fluids by removing metabolic wastes and retaining the proper amounts of water, salts, and nutrients. Components of this system in vertebrates include the kidneys, liver, lungs, and skin.

Not all animals use the same routes or excrete their wastes the same way humans do. Excretion applies to metabolic waste products that cross a plasma membrane. Elimination is the removal of feces.

Nitrogen Wastes

Nitrogen wastes are a by-product of protein metabolism. Amino groups are removed from amino acids prior to energy conversion. The NH2 (amino group) combines with a hydrogen ion (proton) to form ammonia (NH3).

Ammonia is very toxic and usually is excreted directly by marine animals. Terrestrial animals usually need to conserve water. Ammonia is converted to urea, a compound the body can tolerate at higher concentrations than ammonia. Birds and insects secrete uric acid that they make through large energy expenditure but little water loss. Amphibians and mammals secrete urea that they form in their liver. Amino groups are turned into ammonia, which in turn is converted to urea, dumped into the blood and concentrated by the kidneys.


http://smallfry.dmu.ac.uk/chem/mom/urea/urea.html

http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookglossPQ.html#proteins

Water and Salt Balance

The excretory system is responsible for regulating water balance in various body fluids. Osmoregulation refers to the state aquatic animals are in: they are surrounded by freshwater and must constantly deal with the influx of water. Animals, such as crabs, have an internal salt concentration very similar to that of the surrounding ocean. Such animals are known as osmoconformers, as there is little water transport between the inside of the animal and the isotonic outside environment.

Marine vertebrates, however, have internal concentrations of salt that are about one-third of the surrounding seawater. They are said to be osmoregulators. Osmoregulators face two problems: prevention of water loss from the body and prevention of salts diffusing into the body. Fish deal with this by passing water out of their tissues through their gills by osmosis and salt through their gills by active transport. Cartilaginous fish have a greater salt concentration than seawater, causing water to move into the shark by osmosis; this water is used for excretion. Freshwater fish must prevent water gain and salt loss. They do not drink water, and have their skin covered by a thin mucus. Water enters and leaves through the gills and the fish excretory


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system produces large amounts of dilute urine.

Terrestrial animals use a variety of methods to reduce water loss: living in moist environments, developing impermeable body coverings, production of more concentrated urine. Water loss can be considerable: a person in a 100 degree F temperature loses 1 liter of water per hour.

Excretory System Functions

1. Collect water and filter body fluids.

2. Remove and concentrate waste products from body fluids and return other substances to body fluids as necessary for homeostasis.

3. Eliminate excretory products from the body.


http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookglossU.html#urine

Invertebrate Excretory Organs

Many invertebrates such as flatworms use a nephridium as their excretory organ. At the end of each blind tubule of the nephridium is a ciliated flame cell.

As fluid passes down the tubule, solutes

are reabsorbed and returned to the body fluids. Excretory system of a flatworm. Excretory system of an earthworm. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com),

Body fluids are drawn into the Malphigian tubules by osmosis due to large concentrations of potassium inside the tubule. Body fluids pass back into the body, nitrogenous wastes empty into the insect's gut. Water is reabsorbed and waste is expelled from the insect.


http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookglossM.html#Malpighian%20tubules

http://www.whfreeman.com/

http://www.sinauer.com/

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Excretory system of an ant. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com),

Vertebrates Have Paired Kidneys

ALL vertebrates have paired kidneys. Excretion is not the primary function of kidneys. Kidneys regulate body fluid levels as a primary duty, and remove wastes as a secondary one.

The Human Excretory System

The urinary system is made-up of the kidneys, ureters, bladder, and urethra. Notes in Animal Physiology by CCDivina………… 152

The nephron, an evolutionary modification of the nephridium, is the kidney's functional unit. Waste is filtered from the blood and collected as urine in each kidney. Urine leaves the kidneys by ureters, and collects in the bladder. The bladder can distend to store urine that eventually leaves through the urethra.


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The Nephron

The nephron consists of a cup-shaped capsule containing capillaries and the glomerulus, and a long renal tube. Blood flows into the kidney through the renal artery, which branches into capillaries associated with the glomerulus. Arterial pressure causes water and solutes from the blood to filter into the capsule. Fluid flows through the proximal tubule, which include the loop of Henle, and then into the distal tubule. The distal tubule empties into a collecting duct. Fluids and solutes are returned to the capillaries that surround the nephron tubule.

The nephron has three functions:

1. Glomerular filtration of water and solutes from the blood.

2. Tubular reabsorption of water and conserved molecules back into the blood.

3. Tubular secretion of ions and other waste products from surrounding capillaries into the distal tubule.

Nephrons filter 125 ml of body fluid per minute; filtering the entire body fluid component 16 times each day. In a 24 hour period nephrons produce 180 liters of filtrate, of which 178.5 liters are reabsorbed. The remaining 1.5 liters forms urine.


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Urine Production

1. Filtration in the glomerulus and nephron capsule.

2. Reabsorption in the proximal tubule. 3. Tubular secretion in the Loop of

Henle.

Components of The Nephron

Glomerulus: mechanically filters blood

Bowman's Capsule: mechanically filters blood

Proximal Convoluted Tubule: Reabsorbs 75% of the water, salts, glucose, and amino acids

Loop of Henle: Countercurrent exchange, which maintains the concentration gradient

Distal Convoluted Tubule: Tubular secretion of H ions, potassium, and certain drugs.

Kidney Stones

In some cases, excess wastes crystallize as kidney stones. They grow and can become a painful irritant that may require surgery or ultrasound treatments. Some stones are small enough to be forced into the urethra, others are the size of huge, massive boulders (or so I am told).

Kidney Function


http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookglossJK.html#kidney%20stones

Kidneys perform a number of homeostatic functions:

1. Maintain volume of extracellular fluid

2. Maintain ionic balance in extracellular fluid

3. Maintain pH and osmotic concentration of the extracellular fluid.

4. Excrete toxic metabolic by-products such as urea, ammonia, and uric acid.

Hormone Control of Water and Salt

Water reabsorption is controlled by the antidiuretic hormone (ADH) in negative feedback. ADH is released from the pituitary gland in the brain. Dropping levels of fluid in the blood signal the hypothalamus to cause the pituitary to release ADH into the blood. ADH acts to increase water absorption in the kidneys. This puts more water back in the blood, increasing the concentration of the urine. When too much fluid is present in the blood, sensors in the heart signal the hypothalamus to cause a reduction of the amounts of ADH in the blood. This increases the amount of water absorbed by the kidneys, producing large quantities of a more dilute urine.

Aldosterone, a hormone secreted by the kidneys, regulates the transfer of sodium from the nephron to the blood. When sodium levels in the blood fall, Notes in Animal Physiology by CCDivina………… 146

http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookglossH.html#hypothalamus

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http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookglossA.html#antidiuretic%20hormone%20(ADH)

aldosterone is released into the blood, causing more sodium to pass from the nephron to the blood. This causes water to flow into the blood by osmosis. Renin is released into the blood to control aldosterone.

Disruption of Kidney Function

Infection, environmental toxins such as mercury, and genetic disease can have devastating results by causing disruption of kidney function. Many kidney problems can be treated by dialysis, where a machine acts as a kidney. Kidney transplants are an alternative to dialysis.

Gout is a disorder in which humans start to accumulate more than the usual amount of uric acid (caused by either the body manufacturing excess uric acid or the kidneys not excreting enough of it) and since it’s not water-soluble, it gets stored in the body, frequently in toe joints, causing pain and deformation of the joints involved as well as the formation of kidney stones. Traditionally, people who had gout were put on diets low in purines to try to help alleviate the condition. Typically, gout is treated with colchicine, a deadly poison Caffeine and its relatives, theobromine (in cocoa), and theophylline (in tea) are classified as xanthines (a subgroup within the purines), thus it would make sense that people with gout


http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookglossR.html#renin

should be counseled to avoid coffee, tea, and chocolate.

Some insects, notably blowfly larvae (larvae of those shiny green or blue flies) excrete their nitrogenous wastes as allantoin, another purine. Allantoin is known to be a “cell-proliferant,” thus is used to help wounds to heal. For hundreds of years, people have recognized that the presence of blowfly larvae in a gangrenous wound actually helped it to heal better. From about the turn of the century until the invention of a lot of synthetic drugs, blowfly larvae were raised aseptically, and used to treat severe wounds. With the increase in availability of chemicals after World War II, the use of blowfly larvae declined, for some reason, this treatment was necessary and/or preferred over synthetic drugs. It has been found that the fly larvae only eat dead, gangrenous tissue, leaving the live, healthy tissue, and since their nitrogenous waste is allantoin, that stimulates the wound to heal, usually with less scaring. In this procedure, small, sterile larvae are introduced into the wound and, if needed, traded for other small ones when they get big.

We excrete nitrogenous wastes via our kidneys. Our kidneys are located on either side of the spine, just up under the bottom ribs. They are well supplied with blood via the renal artery and renal vein. Urine made in the kidney collects Notes in Animal Physiology by CCDivina………… 148

in the renal pelvis within the kidney, then flows down the ureter to the bladder where it is stored until voided. From the bladder, the urine flows to the outside via the urethra, (which in the male also serves as part of the reproductory tract).

The kidney is composed of an outer layer, the cortex, and an inner core, the medulla. The kidney consists of repeating units (tubules) called nephrons. The “tops” of the nephrons make up or are in the cortex, while their long tubule portions make up the medulla. To the right is a diagram of an individual nephron. Each nephron has a closely associated blood supply. Blood comes in at the glomerulus and transfers water and solutes to the nephron at Bowman’s capsule. In the proximal tubule, water and some “good” molecules are absorbed back into the body, while a few other, unwanted molecules/ions are added to the urine. Then, the filtrate goes down the loop of Henle (in the medulla) where more water is removed (back into the bloodstream) on the way “down”, but the “up” side is impervious to water. Some NaCl (salt) is removed from the filtrate at this point to adjust the amount in the fluid which surrounds the tubule. Capillaries wind around and exchange materials with the tubule. In the distal tubule, more water and some “good” solutes are removed from the urine, while some more unwanted molecules are put in. From there, the urine flows down a Notes in Animal Physiology by CCDivina………… 149

collecting duct which gathers urine from several nephrons. As the collecting duct goes back through the medulla, more water is removed from the urine. The collecting ducts eventually end up at the renal pelvis which collects the urine from all of them. The area where the collecting ducts enter the renal pelvis is a common area for formation of kidney stones, often giving them a “staghorn” shape.

Antidiuretic hormone (ADH) from the pituitary is one factor influencing urine production. ADH promotes water retention by the kidneys, and its secretion is regulated by a negative feedback loop involving blood water and salt balances. ADH helps the kidney tubules reabsorb water to concentrate the urine. When the blood water level is too high (when you’ve been drinking a lot of liquids), this acts as a negative feedback to inhibit the secretion of ADH so more water is released. Ethanol also inhibits secretion of ADH, so a person who consumes a lot of alcoholic beverages could excrete too much water (and maybe even become dehydrated). Many diuretics work by interfering with ADH production, thus increasing the volume of urine produced. These diuretic effects are one reason why a person drinking beer (alcohol) or coffee (caffeine) needs to urinate more frequently.

When a person’s kidneys cease functioning, due to illness or other causes, renal dialysis can be used on a Notes in Animal Physiology by CCDivina………… 150

short-term basis to filter the person’s blood. This is not a perfect process; it can’t do everything a person’s kidneys can. Typically a person is put on renal dialysis as a temporary measure to extend the person’s life until a kidney transplant can be found. While life-saving, this procedure is often very inconvenient and stressful for the person. It requires spending long periods of time, several days a week, hooked up to the dialysis machine: the person’s blood must actually pass into the dialysis machine so the wastes can be filtered out, and then the blood is returned to the person’s body. This, combined with symptoms caused by the renal failure (the inability of the person’s kidneys to function) often preclude working at a job to earn the money to pay for the treatment. People can get by with one kidney, and the closest tissue match for a kidney transplant is often a sibling.

Some diseases and disorders of the excretory system include:

Nephritis is an inflammation of the glomeruli, due to a number of possible causes, including things like strep throat. Symptoms include bloody urine, scant urine output, and edema (swelling/puffliness). Another, more severe form, is due to an autoimmune attack on the glomeruli. Other types of nephritis affect the tubules.


Nephrosis also affects the glomeruli, and is characterized by excretion of abnormally large amounts of protein (often causing “foamy” urine) and generalized edema (water retension/swelling) throughout the whole body, especially noted as “puffy” eyelids. Because these people’s kidneys often do not handle sodium properly, a low-salt diet is usually prescribed. My younger brother developed nephrosis at age 4, and to control it, had to stay on a no-added-salt diet and take prednisone on a regular basis from then until age 16, at which point, his body finally responded positively to being weaned off the drug.

Most urinary tract infections (UTIs) are caused by Gram negative bacteria such as E. coli. If there is an obstruction of the urethra, catheterization may be needed, but as a general rule, catheterization in cases of UTI is contraindicated because it can actually introduce pathogens and make the infection worse. Women tend to acquire more urethral and bladder infections than men, perhaps because the opening of the urethra is closer to the anus. The way a woman cleans the area


after relieving herself can influence her chances of contracting a UTI and/or vaginal infection. When parents are toilet-training toddlers, the common mistake is to wipe young girls from back to front. The toddlers get used to this feeling, and when they start to wipe themselves, they also go from back to front. This technique wipes bacteria from the anal area towards or into the ends of the vagina and urethra. Rather, young girls should be trained to wipe from front to back, and women who were not trained this way should make a conscious effort to change their habits.

There are a variety of types of kidney stones depending on what conditions caused their formation. According to the Merck Manual, these are calcium oxalate (and/or other calcium-based stones), uric acid, cystine, and the other due to magnesium ammonium phosphate or other causes. Stones may be microscopic to large “staghorn” stones that fill the whole renal pelvis. Often, as the stone is passed down the ureter, the person experiences much pain, and the affected kidney may even temporarily become nonfunctional. Stones may be broken up by ultrasound so they can be passed more easily, but large


stones may have to be surgically removed. If possible, the underlying cause of the stone(s) should be identified and alleviated. For example, calcium stones might be caused by anything from a parathyroid gland problem to too much vitamin D to some forms of cancer to a genetic predisposition.

Nervous System

Nervous system performs the three overlapping functions of sensory input, integration and motor output. Its three main functions are sensory input ,integration and motor output to effectors cells.

The central nervous (CNS) integrates information, while the interconnecting nerves of the peripheral nervous system (PNS) communicate sensory and motor signals between the CNS and the rest of the body.

The nervous system is composed of neurons and supporting cells. The CNS (Central Nervous System) consists of the brains and spinal cord.

Central Nervous system


Neurons contain the molecular machinery common to all cells. When not too severely damaged, neurons in peripheral nerves can regrow. Nerve cells are so specialized, however, that they can no longer reproduce by cell division. And even regrowth is impossible in the central nervous system. This is why severe damage to the brain or spinal cord is permanent and can result in muscle or limb paralysis. Messages to activate those structures cannot be carried past the point of injury.

The brain also has a class of cells called glia. Glial cells are shaped to fit into the spaces between neurons. They stabilize the brain's neural circuits and also supplement the metabolic processes of neurons.

The nervous system--the brain, the spinal cord, and the nerves--also controls body activities. The lower parts of the brain control basic functions such as breathing and heart rate as well as body temperature, hunger, and thirst. Above these regions are the centers for sight, sound, touch, smell, and taste, and the regions that direct voluntary muscular activities of the arms and legs. Performed here are the higher functions of integrating and processing information.

The brain receives and sends information by means of nerves, many of which lie partly in the spinal cord. The Notes in Animal Physiology by CCDivina………… 155

spinal cord is protected by the spinal column. Nerves enter and leave the spinal cord at each level of the body, traveling to and from the arms, legs, and trunk. These nerves bring information from the various sense organs. The information is processed by the brain, and then messages are carried back to muscles and glands throughout the body.

The Peripheral Nervous System contains sensory neurons, which transmits information from the internal and external environment of the CNS and motor neurons, which carry information form the CNS to target organs, intermediate neurons of the CNS integrate sensory input and motor outs.

Impulses are action potentials, electrical signals propagated along neurons membranes

The membrane potential of a non-transmitting neuron is due to the unequal distribution of ions, particularly sodium and potassium across the plasma membrane, the cytoplasm is more negatively charged than the extracellular fluid, membrane potential is maintained by differential permeabilities and the sodium-potassium pump.

A stimulus that affects the membranes’ permeability to ion can either depolarize of hyperpolarize the membrane relative the membrane’s resting potential, this local voltage change is Notes in Animal Physiology by CCDivina………… 156

called a graded potential opens voltage-gated sodium channels and the rapid influx of f Na bring the membrane to potential to a positive value, the membrane potential is restored to its normal sting value by the delayed opening of voltage gate K+ channels and by the closing of the Na + channels . a refractory period follows an action potential, corresponding to the period when the voltage-gated Na channels are inactivated.

The all or none generation of an action potential always creates the sample amplitude of voltage change for a given neuron. The frequency of action potential varies with the intensity of the stimulus.

Once an action potential is initiated in axon, a wave of depolarization propagates, a series of action potentials to the end of the axon.

The rate of transmission of a nerve impulse is directly related to the diameter of the axons. Saltatory conduction, a mechanism by which action potential jump between the nodes of ranvier of myelinated axons, speeds nervous impulses in

Nerves, unlike telephone wires with which they are compared, generate their own self-amplified electrical signals--the nerve impulses. The electrical sign of a nerve impulse is an action potential Notes in Animal Physiology by CCDivina………… 157

(AP), and it is generated when a neuron undergoes electrical change. Electrically charged ions are in varying concentrations inside and outside a cell, causing a voltage difference on each side of the cell membrane. In a "resting" neuron the voltage difference is called the resting potential. The inside of a neuron at rest is electrically more negative than the outside, usually by between -50 and -100 millivolts (mV). In this condition the nerve membrane is polarized.

When a voltage change brought on by a stimulus depolarizes the membrane, either of two things happens. If the stimulus is strong enough to breach a critical threshold level, an action potential is fired. If not, the voltage drops back to the resting potential.

An action potential moves along an axon at speeds of up to ten yards per second. The voltage change and depolarization at one end of the axon "flows" to the next point, where the event is duplicated, and so on down the axon until the AP reaches the axon terminals.

Scientists have a fairly clear idea of how APs form in a neuron. When a portion of the membrane is depolarized, special channels in it open and allow an inward rush of sodium ions, which are in higher concentration outside the cell. Then when the positively charged sodium Notes in Animal Physiology by CCDivina………… 158

ions flow into the negatively charged neuron interior, they cause further depolarization by making the interior electrically more positive. This, in turn, opens more channels, allowing more sodium ions to rush in. Once opened, however, the sodium channels slowly close in spite of the depolarization that originally made them open. Channels for outgoing potassium ions are also in the neuron membrane. They, too, open during depolarization but more slowly than the sodium channels. When the potassium channels finally open, positively charged potassium ions flow to the outside of the cell, where they are in lower concentration. As they leave the cell, they hasten the return of the neuron's voltage to its resting level, and the interior again becomes electrically more negative than the exterior.

APs travel faster in some neurons than in others. This is because some have fatty myelin separating short segments of bare axon that are called nodes of Ranvier. In a myelinated axon the action potential jumps from one node to the next instead of traveling along the entire length of the axon as it must in an unmyelinated axon.

Chemical or electrical communication between cells occur at synapses

The membrane potential of a non-transmitting neuron is due to the unequal distribution of ions, particularly sodium Notes in Animal Physiology by CCDivina………… 159

and potassium across the plasma membrane, the cytoplasm is more negatively charged than the extracellular fluid, membrane potential is maintained by differential permeabilities and the sodium-potassium pump.

A stimulus that affects the membranes’ permeability to ion can either depolarize of hyperpolarize the membrane relative the membrane’s resting potential, this local voltage change is called a graded potential opens voltage-gated sodium channels and the rapid influx of f Na bring the membrane to potential to a positive value, the membrane potential is restored to its normal sting value by the delayed opening of voltage gate K+ channels and by the closing of the Na + channels . a refractory period follows an action potential, corresponding to the period when the voltage-gated Na channels are inactivated.

The all or none generation of an action potential always creates the sample amplitude of voltage change for a given neuron. The frequency of action potential varies with the intensity of the stimulus.

Once an action potential is initiated in axon, a wave of depolarization propagates, a series of action potentials to the end of the axon.


The rate of transmission of a nerve impulse is directly related to the diameter of the axons. Saltatory conduction, a mechanism by which action potential jump between the nodes of ranvier of myelinated axons, speeds nervous impulses in

The human brain.

In the human brain, the midbrain and hindbrain make up the brain stem. The medulla oblongata and pons of the hindbrain work together to control homeostatic functions and conduct together to control homeostatic functions and conduct sensory and motor signals between the spinal cord and higher brain centers. The cerebellum of the hindbrain coordinates movement and balance.The midbrain receives, integrates and protects sensor information of the forebrain.

The forebrain is the site of the most sophisticated neurons processing with major integrating centers in the thalamus, hypothalamus and cerebrum. The thalamus routes neural input to specific areas of the cerebral cortex the outer gray matte of the cerebrum. The function of the hypothalamus range form hormone production to the regulation of body temperature hunger , thirst, sexual response, the fight o fight response and biorhythms


The cerebral cortex contains distinct somatosensory motor areas, which directly process information and association areas, which integrate information. Imaging technology enables researchers to identify specific integrating centers in the functioning brain.

Several areas in the cerebrum and brain stem the most important being the reticular formation, which filters the sensory input sent to the cortex, control sleep and arousal.

The two cerebral hemispheres control different function, Speech, language and analytical ability are centers in the left hemispheres whereas spatial perception and artistic ability predominate in the right. Nerve tracts of the corpus collosum link the two side and allow the brain to function as an integrated whole.

Human emotions are believed to originate from interactions between the limbic system , a group of nuclei in the diencephalons and inner cerebrum, the limbic system interacts closely with the prefrontal cortex, a higher integrative control of the forebrain.

Human memory consists of short term and long-term memories. the process of learning fact appears to differ from that of learning skills. The hippocampus and amygdala. Two components of the limbic Notes in Animal Physiology by CCDivina………… 162

system participate in the circular pathways involved in fact memory.

A functional change at synapses, called long-term potentiation (LTP) may underlay memory stage and learning. Resulting from repeated burst of action potential or LPG is heightened sensitivity to a single action potential by a postsynaptic membrane. Mammalian Nervous System

NEURAL evolution has reached its present peak within the Class Mammalia-but read that "within" with understanding. Most mammals in fact have a brain that is little more developed in a mental sense than that of birds. Here it is very easy to slip into teleology and anthropomorphic chauvanism. Wow. Anyway, in your enthusiasm with having a mind, keep in your mind that evolution is fully at work and the most stupid duckbill knows more about how to be a duckbill than you ever could.

The mammalian brain has made major advancements within two regions. The cerebellum has expanded greatly in volume, but more importantly, it has become much folded in all species. The cerebellar cortex is vastly increased in surface area by this folding into many folia. Cortical cells interrelate in an inclosed grouping (called a "column" or "barrel") that is perpendicular to the cortical surface. The greater the surface area (not volume), the more Notes in Animal Physiology by CCDivina………… 163

numerous these columns can be...and, thus, the greater the processing capacity. The human cerebellum is about the size of a human fist, yet if the folding were flattened, the cerebellum would be about 45 cm wide and 25 m long to yield a rather strangely shaped cranium.

The cerebellum has only a vague local sign...that is, association with a particular body region. Further, it is always active, whether the muscular system is busy or not. An understanding of its general function was gained early on, because this is the only brain region which can be removed surgically and have the subject survive and thrive (but not unchanged). In fact, although the cerebellum itself is not involved with Parkinsonism, it does receive faulty input from higher motor centers that result in characteristic tremors. An early surgical remedy involved cerebellumectomy, which did nothing for the course of the disease but did relieve palsy symptoms.

Cerebellar function in lower vertebrates centers around muscular coordination with sense of balance to maintain body position. At some point in subsequent evolution of this brain division, it began to take on other functions. All proprioceptive (muscle and joint sense) input to the brain is referred (only) to the cerebellum in mammals. In addition all locomotor and Notes in Animal Physiology by CCDivina………… 164

postural motor decisions are referred to cerebellar cortex before implementation. The cerebellum then compares the present position of the body relative to the center of the earth, the angle subtended by all joints, and the current effort being put out by the muscular system-all of these factors are compared with the instructions about to be issued by cerebral motor centers. The cerebellum then "advises" the cerebrum how best to achieve its goal, considering what the body is presently doing.

Many cerebral functions have exact local sign, such as sense of touch, precise motor control, and the special senses of vision and hearing (pitch). The sides and apices of gyri have larger number of neurons and of synapses, and the cortex itself is thicker, compared to the floor of a sulcus. Thus, it is not surprising that such primary areas often have precise functional boundaries that correspond to the floors of sulci. A gyrus may not only be specifically identified with a particular operation, but there may be linear correlations along the length of that gyrus with particular aspects. For example, both of the temporal lobe gyri in humans that are responsible for appreciation of sense of touch and for very precise motor control can be mapped from ventral to dorsal in a distorted but recognizable figure of the body. Notes in Animal Physiology by CCDivina………… 165

These distortions represent variation in sensitivity or precision. For instance, the areas devoted to fingers (sensory and motor) are larger than gyral area representing the entire body trunk.

The three meninges of the CNS-respectively pia mater, arachnoid, and outermost dura mater-was well differentiated in mammals. Unlike most vertebrate forms, the brain lies close against the inner layer of the skull. This relationship is displayed in many gyrencephalic mammals as negative ridges and grooves representing the folding patterns of the cerebral and cerebellar cortices. This creates a kind of fossil brain image, and endocasts of extinct species permits study of brain evolution in ancient forms. This patterning does not develop in human crania except for the imprint of surface blood vessels.

FREQUENTLY ASKED QUESTIONS

What is the difference between a neuron and a glial cell?

Neurons and glial cells are the basic components of neural control system. The neurons or nerve cell is the fundamental information-processing units, receiving and integrating information Notes in Animal Physiology by CCDivina………… 166

from external and internal environment, and using this information to control effectors (muscles and glands. The neuron has two specialized properties for this task: irritability or excitatory and conductivity. Irritability – a property fond to some degree in all cells – is the capacity to respond to environmental stimuli for a neuron, these stimuli are conducted messages in the form of electrochemical impulses coming to it from sensory receptors and other neurons, the neuron responds to theses stimuli by passing o its own flow of coded electrochemical impulses. The term conductivity, when used with a wire in an electric circuit, referred to wire’s ability to carry or conduct an electric current with a neuron, conductivity is the ability to conduct a current of electrochemical impulses along its own length an the to transmit to the next neuron or effectors.

The other basic component of the neural control system, the glial (or neuroglial) cells as their name implies, “glue” the neural systems together. Because glial cells surround the neurons, they are able to insulate neurons form the rest of the body and provide them with many life-support services glial cells bring neurons the substances for the rest of the body and provide them with many life-support services. Glial cells bring neurons the substances for metabolism, remove metabolism wastes and debris from damaged or dead neurons, and Notes in Animal Physiology by CCDivina………… 167

regulate the chemistry of the fluid bathing the neurons. Insulate the neurons form each other to prevent interference between the electrochemical message channels and provide myelin sheaths for salutatory conduction. There are many types of glial cells, astrocytes, which form the brood-brain barrier by lining brains capillaries. Oligodendroglial cells, which are the glial support cells for the vertebrate central nervous system ( brain and spinal cord and Schwann cells, which perform the latter function in the vertebrate peripheral nervous system, .

Three major trends that affected the evolution of nervous systems are centralization, the change from radial o bilateral symmetry and cephalization. What are these trends and how did they affect this evolution.

Because the neural tissues are rarely preserved in fossils, scientist have had to piece together the early evolution of nervous systems for stages seen n living representative of early animal. Of these, it now seem that modern cnidarians, ( sea anemones. Hydra, jellyfish) are most similar to the fires animals to have neurons and nervous systems/.

The modern cnidarians are radially symmetrical: there is no front and back or right and left sides, instead the body Notes in Animal Physiology by CCDivina………… 168

parts are organized circularly, like spokes radiating from the center of a wheel. The cnidarians have identical neurons interconnected by synapses crisscross the body. The net transmits information from sensory receptors cell to muscle like effectors cell. When the sensory cell react to chemical or mechanical stimuli, the receptor glial cell to like effectors cells. When the sensory cells react to chemical or mechanical stimuli, the neuron message radiates outward along the net in all direction’s producing contractions in large number of effectors cells. This allows some degree of coordination of localized responses, such as the movement of a tentacle .

Also seen in a modern cnidarians, the jellyfish , is somewhat more advanced nervous system that showed the first evidence of centralization: the gathering together of neuron to form control center’s in he jellyfish, this takes the form a ring of neurons around its bell-shaped body, the ring produces coordinated whole-body swimming movements.

A major advancement in the evolution of nervous systems accompanied the appearance of animals with bilaterally symmetrical bodies, which are organized on a longitudinal axis with right and left sides that are mirror images of each other. This type of body has a distinct


anterior end and posterior end, dorsal surface and ventral surface.

The first simplest animals to exhibit this type of organization were the flatworms, represented today by such forms as the planarian, these animals show an increasing centralization, with neurons gathered together to form pathways and control center. Bundles containing the somas and fibers of neurons form two parallel nerve controls that extent the full length of the body. In the animal end, or head , the nerve cord fuse to form ganglion ( a collection of somas and synapses.)_ this accumulation of neural tissue in the head end is thought to represent the first example of evolutionary terms called cephalization. Although this planarian cephalic (situated in the head ganglion is quit primitive, it has been called the first brain)

Increasing centralization and cephalization occurred in the evolution of the bilateral nervous system, in both the invertebrates (annelids, mollusks, cephalopods, arthropods and vertebrates. In many advanced invertebrate, there is a central nervous system consisting of paired , solid ventral nerve cords with glia in each segment of the body, and a dominant ganglion,(brain) in the head, In vertebrates, the central nervous system is a single, hollow, dorsal nerve cord (the spinal cord with no conspicuous segmental ganglia and with a large doming brain in the head.Notes in Animal Physiology by CCDivina………… 170

You are watching a horror movie and you notice that your heart is beating fast, your mouth is dry and you a breathing rapidly.

You are experiencing some f the more noticeable components of the fight-or fight response produce by the sympathetic division of the autonomic nervous system. In general, the sympathetic systems prepares and animal to respond to an emergency, to be able to fight it or flee from it, which the other autonomic divisions, the parasympathetic system, works to restore than conserve energy. It is seen there that most but not all , body organs are innate by both systems, and often they have opposite (antagonistic effects on the same organs. One major difference between the systems are while the parasympathetic exits the central nervous system in the cranial and sacral nerves, the sympathetic exits through thoracic and lumbar nerve, whole preganglionic sympathetic neurons synapse with post ganglion fibers in a chain of sympathetic ganglia enter and on both sides of the spinal cord an the parasympathetic system, the synapse between preganglions and postganglionic takes place near the innervated ova.

How does environments information reach the central nervous system?


An animals’ response to a change into its external internal environments coordinated by its central nervous system, environmental information must therefore be converted into neural master before a response se can take place. An environment change usually involves some form of energy. The conversion of the environmental energy into the electrochemical energy of nerves is called transduction and is performed by sensory cells.

Transduction and the transmission of traduced information along afferent neural pathways may be performed by a single sensory cell or by a group of sensory cells organized into a sensory organ. When a single sensory cell both traduces and transmits information, it is called sensory neurons. The cell membrane enclosing dendrites of the neuron responds to a particular form of environmental energy by altering its permeability to ions, which cause a change in the membrane potential. the new potential is the generator potential of the sensory neurons and if large enough, initiates at n action potential in the icon that revels to the central nervous site, Generate potential vary greatly on value, they can be larger or smaller than action potential, which always have the same vale.

When sensory perform both Notes in Animal Physiology by CCDivina………… 172

transduction and transmission, some of the cells are involved in transduction, some are accessory structures and others are sensory neuron ah transits the information to the Central nervous system, Accessory structure focus, amplify or localize the environmental energy before it transducers. The lens of a vertebrate eye. For example bends the light so that it converges into the retina. The energy is then transude by receptors cells when the permeability of their membrane I as so altered that ionic flow changes them membrane potential. The altered potential; in a receptor cell is called a receptor potential. Like the generator potential, the receptor potential may be smaller of larger than an action potential, if large enough , the receptor potential alters the membrane potential in the sensory neurons to which it is connected by a synapse. This change may initiate an action potential in the axon of the sensory neuron, the nerve impulse is then conveyed along eh afferent pathway the central nervous system.

Its sensory cells accomplish all detection by an animal of the environmental external to the animal’s nervous system. Each type of sensory cell is sensitive to a certain form of energy, such as heat, light or sounds. An animal can receive information only if it has sensory cells that are capable of transuding the form of energy accompanying the environmental event. An Notes in Animal Physiology by CCDivina………… 173

animals’ sensory cells result from natural selection and vary for different species. A humans lack suitable sensory cells form any forms of energy, including x-ray , radar and radio or television waves, we detect such phenomena only after they have been converted by mechanical devise into forms of energy that our sensory cells can recognize, many animals can detect environmental phenomenon that we cannot. Bees see ultraviolet radiation, bats and porpoises hear very high-pitched sounds, snakes lock prey by sensing the heat emanating from their prey’s bodies and some fishes detect prey and mate by means of electrical currents. Most animals have sensory cells that respond to mechanical, chemical thermal pain and electromagnetic stimuli.

THE ENDOCRINE SYSTEMThe nervous system coordinates rapid

and precise responses to stimuli using action potentials. The endocrine system maintains homeostasis and long-term control using chemical signals. The endocrine system works in parallel with the nervous system to control growth and maturation along with homeostasis.

Hormones

The endocrine system is a collection of glands that secrete chemical messages we call hormones. These signals are passed through the blood to arrive at a Notes in Animal Physiology by CCDivina………… 174

http://gened.emc.maricopa.edu/Bio/BIO181/BIOBK/BioBookglossH.html#hormones

http://gened.emc.maricopa.edu/Bio/BIO181/BIOBK/BioBookglossH.html#homeostasis

http://gened.emc.maricopa.edu/Bio/BIO181/BIOBK/BioBookglossE.html#endocrine%20system

http://gened.emc.maricopa.edu/Bio/BIO181/BIOBK/BioBookglossA.html#action%20potential

http://gened.emc.maricopa.edu/Bio/BIO181/BIOBK/BioBookglossN.html#nervous%20system

target organ, which has cells possessing the appropriate receptor. Exocrine glands (not part of the endocrine system) secrete products that are passed outside the body. Sweat glands, salivary glands, and digestive glands are examples of exocrine glands.

The roles of hormones in selecting target cells and delivering the hormonal message. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com).




Hormones are grouped into three classes based on their structure: steroids, peptides and amines Steroids

Steroids are lipids derived from cholesterol. Testosterone is the male sex hormone. Estradiol, similar in structure to testosterone, is responsible for many female sex characteristics. Steroid hormones are secreted by the gonads, adrenal cortex, and placenta.


http://gened.emc.maricopa.edu/Bio/BIO181/BIOBK/BioBookglossPQ.html#placenta

http://gened.emc.maricopa.edu/Bio/BIO181/BIOBK/BioBookglossG.html#gonads

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Structure of some steroid hormones and their pathways of formation. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com).Peptides and Amines

Peptides are short chains of amino acids; most hormones are peptides. They are secreted by the pituitary, parathyroid, heart, stomach, liver, and kidneys. Amines are derived from the amino acid tyrosine and are secreted from the thyroid and the adrenal medulla.


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Solubility of the various hormone classes varies.Synthesis, Storage, and Secretion

Steroid hormones are derived from cholesterol by a biochemical reaction series. Defects along this series often lead to hormonal imbalances with serious consequences. Once synthesized, steroid hormones pass into the bloodstream; they are not stored by cells, and the rate of synthesis controls them.

Peptide hormones are synthesized as precursor molecules and processed by the endoplasmic reticulum and Golgi where they are stored in secretory granules. When needed, the granules are dumped into the bloodstream. Different hormones can often be made from the same precursor molecule by cleaving it with a different enzyme.

Amine hormones (notably epinephrine) are stored as granules in the cytoplasm until needed.

Evolution of Endocrine Systems

Most animals with well-developed nervous and circulatory systems have an endocrine system. Most of the similarities among the endocrine systems of crustaceans, arthropods, and vertebrates are examples of convergent evolution. The vertebrate endocrine system consists of glands (pituitary, thyroid, adrenal), and diffuse cell groups scattered in epithelial tissues.Notes in Animal Physiology by CCDivina………… 178

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More than fifty different hormones are secreted. Endocrine glands arise during development for all three embryologic tissue layers (endoderm, mesoderm, ectoderm). The type of endocrine product is determined by which tissue layer a gland originated in. Glands of ectodermal and endodermal origin produce peptide and amine hormones; mesodermal-origin glands secrete hormones based on lipids.

Endocrine Systems and Feedback Cycles

The endocrine system uses cycles and negative feedback to regulate physiological functions. Negative feedback regulates the secretion of almost every hormone. Cycles of secretion maintain physiological and homeostatic control. These cycles can range from hours to months in duration.

Negative feedback in the thyroxine release reflex. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer


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Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com

Mechanisms of Hormone Action

The endocrine system acts by releasing hormones that in turn trigger actions in specific target cells. Receptors on target cell membranes bind only to one type of hormone. More than fifty human hormones have been identified; all act by binding to receptor molecules. The binding hormone changes the shape of the receptor causing the response to the hormone. There are two mechanisms of hormone action on all target cells.

Nonsteroid Hormones Nonsteroid hormones (water soluble)

do not enter the cell but bind to plasma membrane receptors, generating a chemical signal (second messenger) inside the target cell. Five different second messenger chemicals, including cyclic AMP have been identified. Second messengers activate other intracellular chemicals to produce the target cell response.


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The action of nonsteroid hormones. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com),

Steroid Hormones

The second mechanism involves steroid hormones, which pass through the plasma membrane and act in a two step process. Steroid hormones bind, once inside the cell, to the nuclear membrane receptors, producing an activated hormone-receptor complex. The activated Notes in Animal Physiology by CCDivina………… 181



hormone-receptor complex binds to DNA and activates specific genes, increasing production of proteins.

The action of steroid hormones. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com),

Endocrine-related Problems are due to overproduction of a hormone or underproduction of a hormone or even nonfunctional receptors that cause target cells to become insensitive to hormones

The Nervous and Endocrine Systems

The pituitary gland (often called the master gland) is located in a small




bony cavity at the base of the brain. A stalk links the pituitary to the hypothalamus, which controls release of pituitary hormones. The pituitary gland has two lobes: the anterior and posterior lobes. The anterior pituitary is glandular.

The endocrine system in females and males. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com)

The hypothalamus contains neurons that control releases from the anterior pituitary. Seven hypothalamic hormones are released into a portal system connecting the hypothalamus and pituitary, and cause targets in the pituitary to release eight hormones.


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The location and roles of the hypothalamus and pituitary glands. Images from Purves et al., Notes in Animal Physiology by CCDivina………… 184

Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com),

Growth hormone (GH) is a peptide anterior pituitary hormone essential for growth. GH-releasing hormone stimulates release of GH. GH-inhibiting hormone suppresses the release of GH. The hypothalamus maintains homeostatic levels of GH. Cells under the action of GH increase in size (hypertrophy) and number (hyperplasia). GH also causes increase in bone length and thickness by deposition of cartilage at the ends of bones. During adolescence, sex hormones cause replacement of cartilage by bone, halting further bone growth even though GH is still present. Too little or two much GH can cause dwarfism or gigantism, respectively.

Hypothalamus receptors monitor blood levels of thyroid hormones. Low blood levels of Thyroid-stimulating hormone (TSH) cause the release of TSH-releasing hormone from the hypothalamus, which in turn causes the release of TSH from the anterior pituitary. TSH travels to the thyroid where it promotes production of thyroid hormones, which in turn regulate metabolic rates and body temperatures.

Gonadotropins and prolactin are also secreted by the anterior pituitary. Gonadotropins (which include follicle-stimulating hormone, FSH, and luteinizing hormone, LH) affect the gonads by stimulating gamete formation and


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production of sex hormones. Prolactin is secreted near the end of pregnancy and prepares the breasts for milk production.

The Posterior PituitaryThe posterior pituitary stores and releases hormones into the blood. Antidiuretic hormone (ADH) and oxytocin are produced in the hypothalamus and transported by axons to the posterior pituitary where they are dumped into the blood. ADH controls water balance in the body and blood pressure. Oxytocin is a small peptide hormone that stimulates uterine contractions during childbirth.

Other Endocrine Organs

The Adrenal Glands

Each kidney has an adrenal gland located above it. The adrenal gland is divided into an inner medulla and an outer cortex. The medulla synthesizes amine hormones, the cortex secretes steroid hormones. The adrenal medulla consists of modified neurons that secrete two hormones: epinephrine and norepinephrine. Stimulation of the cortex by the sympathetic nervous system causes release of hormones into the blood to initiate the "fight or flight" response. The adrenal cortex produces several steroid hormones in three classes: mineralocorticoids, glucocorticoids, and sex hormones. Mineralocorticoids maintain electrolyte balance. Glucocorticoids produce a long-term, slow response to Notes in Animal Physiology by CCDivina………… 186

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stress by raising blood glucose levels through the breakdown of fats and proteins; they also suppress the immune response and inhibit the inflammatory response.

The structure of the kidney as relates to hormones. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com),

The Thyroid Gland

The thyroid gland is located in the neck. Follicles in the thyroid secrete thyroglobulin, a storage form of thyroid hormone. Thyroid stimulating hormone (TSH) from the anterior pituitary causes conversion of thyroglobulin into thyroid hormones T4 and T3. Almost all body cells are targets of thyroid hormones.

Thyroid hormone increases the overall metabolic rate, regulates growth and development as well as the onset of Notes in Animal Physiology by CCDivina………… 187



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sexual maturity. Calcitonin is also secreted by large cells in the thyroid; it plays a role in regulation of calcium. The Pancreas

The pancreas contains exocrine cells that secrete digestive enzymes into the small intestine and clusters of endocrine cells (the pancreatic islets). The islets secrete the hormones insulin and glucagon, which regulate blood glucose levels.After a meal, blood glucose levels rise, prompting the release of insulin, which causes cells to take up glucose, and liver and skeletal muscle cells to form the carbohydrate glycogen. As glucose levels in the blood fall, further insulin production is inhibited. Glucagon causes the breakdown of glycogen into glucose, which in turn is released into the blood to maintain glucose levels within a homeostatic range. Glucagon production is stimulated when blood glucose levels fall, and inhibited when they rise. Diabetes results from inadequate levels of insulin. Type I diabetes is characterized by inadequate levels of insulin secretion, often due to a genetic cause. Type II usually develops in adults from both genetic and environmental causes. Loss of response of targets to insulin rather than lack of insulin causes this type of diabetes. Diabetes causes impairment in the functioning of the eyes, circulatory system, nervous system, and failure of the kidneys. Diabetes is the second leading cause of Notes in Animal Physiology by CCDivina………… 188

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blindness in the US. Treatments involve daily injections of insulin, monitoring of blood glucose levels and a controlled diet.

Other Chemical Messengers

Interferons are proteins released when a cell has been attacked by a virus. They cause neighboring cells to produce antiviral proteins. Once activated, these proteins destroy the virus.

Prostaglandins are fatty acids that behave in many ways like hormones. They are produced by most cells in the body and act on neighboring cells.

Pheromones are chemical signals that travel between organisms rather than between cells within an organism. Pheromones are used to mark territory, signal prospective mates, and communicate. The presence of a human sex attractant/pheromone has not been established conclusively.

Biological Cycles

Biological cycles ranging from minutes to years occur throughout the animal kingdom. Cycles involve hibernation, mating behavior, body temperature and many other physiological processes.

Rhythms or cycles that show cyclic changes on a daily (or even a few hours) Notes in Animal Physiology by CCDivina………… 189

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basis are known as circadian rhythms. Many hormones, such as ACTH-cortisol, TSH, and GH show circadian rhythms.

The menstrual cycle is controlled by a number of hormones secreted in a cyclical fashion. Thyroid secretion is usually higher in winter than in summer. Childbirth is hormonally controlled, and is highest between 2 and 7 AM.

Internal cycles of hormone production are controlled by the hypothalamus, specifically the suprachiasmic nucleus (SCN). According to one model, the SCN is signaled by messages from the light-detecting retina of the eyes.The SCN signals the pineal gland in the brain to signal the hypothalamus, etc.

From http://gened.emc.maricopa.edu/

Questions and Answers

Surgical removal of the posterior pituitary in experimental animals results in marked symptoms, but these symptoms associated with hormone shortage are temporary. Explain these results.

Answer

The cell bodies of the neurosecretory cells that produce ADH are in the hypothalamus and their axons


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extend into the posterior pituitary, where ADH is stored and secreted. Removing the posterior pituitary severs the axons, resulting in a temporary reduction in the secretion. However, the cell bodies still produce ADH. And as ADH accumulates at the ends of severed axons, ADH secretion resumes.

Mr. Pablo has a son who wants to be a basketball player almost as much as Mr. Pablo wants him to be one. Mr. Pablo knows a little about growth hormone and asked his son’s doctor is he would prescribe some for his son so he can grow tall. What do you think the doctor tells Mr. Pablo?

Answer:If GH is administered to young people

before growth of their long bones is complete, it will cause their long bone to grow and they will grow taller. However, GH would have to be administered over considerable length of time. It is likely that some symptoms of acromegaly would develop. In addition to undesirable changes in the skeleton, nerves frequently are compressed as a result of the proliferation of connective tissue. Because GH spares glucose usage chronic hyperglycemia results frequently leading to diabetes mellitus and the development of severe atherosclerosis.


An enlargement of the thyroid gland, called a goiter, develops when there is too little iodine in the diet. Explain why the thyroid gland enlarges in response to iodine deficiency in the diet?

AnswerThe thyroid gland enlarges in response to iodine deficiency because without iodine, thyroid hormones cannot be synthesized. Consequently, TSH levels in the circulatory system increase because of the lower than normal levels of thyroid hormone in the blood. Increased TSH levels cause the thyroid gland to enlarge because it continues to stimulate thyroglobulin synthesis in large amounts. The thyroid follicles enlarge; even the thyroid hormones cannot be produced.

Predict the effect of an inadequate dietary intake of calcium on PTH secretion and on target tissues for PTH.

AnswerIn response to the reduced dietary

intake of calcium the blood levels of calcium begin to decline. In response to the decline in blood levels of calcium there is an increase of PTH from the parathyroid glands. The PTH functions to increase calcium resorption from bone. Consequently, blood levels of calcium are maintained within the normal range but at Notes in Animal Physiology by CCDivina………… 192

the same time bones are being decalcified. Severe dietary calcium deficiency will result in bones that become soft and eaten away because of the decrease in calcium content.

A patient with a malignant tumor has his thyroid gland removed, what effect would this removal have on blood levels of thyroid hormone, TRH, TSH and calcitonin. What would result if the parathyroid glands were inadvertently removed during surgery?

Answer:Removal of the thyroid gland would

remove the tissue responsible for thyroid hormone production (follicles), calcitonin (parafollicular cells) and the PTH, (parathyroid are embedded in the thyroid gland). Therefore, thyroid hormones, calcitonins and PTH would no longer be found in the blood. Without the negative feedback effect of thyroid hormones. TRH and TSH levels in the blood would increase. Without, PTH blood levels of calcium would fall. When blood levels of calcium fall below normal, the permeability of nerve and muscle cells to solid increases. As a consequence, spontaneous action potentials are produced that cause tetanus of muscles. Death can result from tetany of respiratory muscle

Alterations in blood levels of sodium and potassium have profound


effects in the electrical properties of cells. Because high blood levels of aldosterone cause retention of sodium and excretion of potassium. Predict and explain the effects of high aldosterone levels on nerve and muscle function. Conversely, because low blood levels of aldosterone cause low blood levels of sodium and elevated blood levels of potassium. Predict the effects of low aldosterone levels on nerve and muscle function.

Answer:High aldosterone level in the blood

lead to elevated sodium levels in the circulatory system and low blood levels of potassium .the effect of low blood levels of potassium would be hyperpolarization of muscle and neurons. The hyperpolarization results form a greater tendency of potassium to diffuse form the cell. As a result, a greater than normal stimulus is required to cause the cells to depolarize to threshold and generate an action potential. Thus the symptoms include lethargy and muscle weakness. The elevated sodium concentration would result in a greater than normal amount of water retention in the circulatory system which can result in elevated blood pressure.

The major effect of a low rate of aldosterone secretion is elevated blood potassium levels. As a result nerve and muscle cells depolarize, Because of their partial depolarization they produce Notes in Animal Physiology by CCDivina………… 194

action potentials spontaneously or in response to very small stimuli. The result is a muscle spasms or tetany.

1. Cortisons, a drug similar to cortisol, is sometimes given to people who have severe allergies, taking this substance chronically can damage the adrenal cortex. Explain how this damage can occur?

Answer

Large doses of cortisone can damage the adrenal cortex because cortisone inhibits ACTH secretion from the anterior pituitary. ACTH is required to keep adrenal cortex from undergoing atrophy. Prolonged use of larges dose of cortisone can cause the adrenal gland to atrophy to the point at which it cannot recover is CTH level do increase again.

Explain they the increase in insulin secretion in response to parasympathetic stimulation and gastrointestinal hormones is consistent with the maintenance of blood glucose levels in the circulatory system

Answer An increase in insulin secretion in

response to parasympathetic stimulation and gastrointestinal hormones is consistent with the maintenance of homeostasis because parasymtpatic t stimulation increased gastrointestinal hormones result from condition such as Notes in Animal Physiology by CCDivina………… 195

eating a meal therefore, insulin levels increase just before large amounts of glucose and amino acids enter the circulatory system. The elevated insulin levels prevents a large increase in blood glucose and the loss of glucose in the urine

Compare the regulation of glucagons and insulin secretion after a meal high in carbohydrate aw after a meal low in carbohydrate but high in proteins and during physical exercise.

Answer

In response to a meal high in carbohydrates, insulin secretion is increased and glucagon secretion is reduces. The stimulus for the insulin secretion comes form parasympathetic stimulation and more important, from elevated blood levels of glucose, in response to a meal high in protein but low in carbohydrates, insulin secretion is increased slightly and glucagons secretion is also increased. The stimulation for insulin secretion is parasympathetic stimulation and d an increase in blood amino acid level. Glucagon secretion is stimulated by low blood glucose level and by some amino acids.

During periods of exercise, sympathetic stimulation inhibits insulin secretion. As blood glucose level


decline, there is an increase of glucagon secretion

Explain why long distance runners may have much of a “kick” left when they try to sprint to the finish line.

Answer: Sympathetic stimulation during

exercise inhibits insulin secretion and blood glucose level not high because of the rapid metabolism of the small amount of glucose that can enter the muscles. Much of the energy for muscle contraction depends on glucose stored in the form of glycogen in muscles and during the end of the race results from increased energy production through anaerobic respiration, which uses glucose or glycogen as an energy source. Because blood glucose levels and glycogen levels are low, there is insufficient source of energy for greatly increased muscle activity.
