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Advanced Human Physiology Marines Acevedo Marimar de la Cruz
The Kidney
• The functions of the kidneys
o Removal of metabolic wastes from the blood o Maintenance of blood pH o Control of blood volume
o Regulation of erythrocyte levels o Metabolism of vitamin D
• Localization
o Posterior to the abdominal wall within an area called retroperitoneum • Structures
o Renal capsule: the outer region of the entire kidney
o Renal fat pad: fat tissue that surrounds the renal capsule and cushions the kidney from mechanical shock.
o Renal fascia: connective tissue that attaches the kidneys to the abdominal wall
o Hilum: area where the renal veins exits, renal arteries enters and nerves enters. o Renal sinus: contains the renal pelvis, renal calyces, blood vessels, nerves, and fat tissue. o Renal cortex: outer portion of the kidney, occurs between the renal capsule and renal
medulla. o Renal medulla: inner portion of the kidney
Renal pyramids: striped appearance as a result of parallel-‐arranged nephron
tubules. • Renal papillae: tips of the renal pyramids • Minor calyces: surround a renal papilla. 8-‐20 of these occur within a kidney
• Mayor calyces: formed by the merging of adjacent minor calyces • Renal pelvis: enlarged region that results from the merging of mayor calyces • Ureter: directs urine from the renal pelvis to the urinary bladder.
• The Nephron o Basic functional unit of the kidney. o Each nephron function with a systemic arteriole to simultaneously generate blood (with
elevated hematocrit) and a fluid (filtrate) o The nephron tubule removes substances from the filtrate that are retained in the body
and are return to the high hematocrit blood in the specialized capillaries. At the same time
the wastes from the capillary blood are removed and delivered to the filtrate. • The nephron and associated components
o Afferent arteriole: brings systemic blood to the glomerulus.
o Glomerulus: capillaries are fenestrated. Blood from the afferent arterioles enters these capillaries and the pressure favors the passage of components making the blood plasma to
enter Bowman’s space (form the initial filtrate)
o Efferent arteriole: channels blood away from the glomerular capillaries on to the
peritubular capillaries. o Peritubular capillaries: branch and surround the nephron tubule. Eventually join to
interlobular veins.
o Bowman’s capsule: encloses the glomerulus. Parietal layer: made up of simple squamous epithelium. Outer layer. Visceral layer: inner layer. Made up of unique cells (podocytes – form filtration slits
where plasma components can leave the capillary vessel and enter Bowman’s space) o Bowman’s space: the fluid-‐filled space between the inner margin of Bowman’s capsule
and the glomerular capillaries.
o Renal corpuscle: the combination of Bowman’s capsule, space, and the peritubular capillaries.
o Proximal convoluted tubule: part of the nephron tubule that is connected and receives
filtrate from Bowman’s space. Made of single layer of simple cuboidal epithelium. Cells contain microvilli at the surface of the nephron lumen.
o Henle’s loop: made of 2 segments (most is contain in the renal medulla) Descending limb: made up of simple cuboidal epithelium (first part), then it is made
of simple squamous epithelium.
Ascending limb: made up of simple squamous epithelium. It thickens and is made up of simple cuboidal epithelium.
o Distal convoluted tubule
made up of simple cuboidal epithelium have less microvilli directs the filtrate to the collecting duct
o collecting duct made of simple cuboidal epithelium directs the filtrate to the tip of the renal pyramid.
o Blood is brought to each kidney by a renal artery (branch off of the abdominal aorta) Renal arteries branch to form segmental arteries that give rise to interlobar
arteries. They then branch and form the afferent arterioles (take blood to the
glomerular capillaries) o Blood exiting the glomerular capillaries is carry by the efferent arterioles. These branches
to form the peritubular capillaries (surround the nephron tubule). The peritubular
capillaries direct blood to the interlobular veins, which then takes the blood to the arcuate vein. This one directs blood to interlobar veins which takes blood to the renal vein.
• Production of Urine
o Involves reabsorption and secretion Reabsorption: substances are transferred from the filtrate back into the blood
Secretion: movement (active transport processes) of substances into the nephron tubule so that these can be part of the filtrate.
• Filtrate
o Renal flow rate 1176ml/min
o Glomerular filtration rate/GFR (totals about 189L of fluid each day) o More than 99% of the filtrate is reabsorbed o Filtration barrier: composed of endothelium of the glomerular capillaries, the basilar
membrane surrounding this epithelium, and podocytes. o Glomerular capillaries have abundant fenestrae making them more permeable than other
capillaries.
o The protein hormones and albumin that pass to the Bowman’s space are then metabolize by the proximal convoluted tubule (healthy individuals have little protein in urine)
o Blood coming into the glomerular capillaries have a pressure of 60mmHg.
32mmHg colloid osmotic pressure in the capillary lumen and 18mmHg pressure in Bowman’s space. There is a net force of +10mmHg glomerular capillary fluid pressure that causes components of the plasma to cross the filtration barrier and
form filtrate. Per minute this results in 125mL of the total 650mL renal plasma flow to become
filtrate.
o Higher concentration of water inside Bowman’s space. Osmotic pressure favors water moving from Bowman’s space to the capillary
lumen.
• Nephron Reabsortion o Substances removed from the filtrate are: salts, organic molecules, amino acids, and
simple sugars, Na+, K+, Ca2+, HCO3-‐ and Cl-‐.
Secondary active transport processes move the filtrate solutes from the nephron tubule into the interstitium.
o Na – K pump causes: low [Na+] inside the nephron epithelial cells and high [Na+] inside
the lumen of the nephron. Na concentration gradient provides the energy needed to move other substances
out of the nephron lumen and into the epithelial cells.
Carriers molecules use Na+ gradient energy to move Cl-‐, K+, amino acids, and glucose from the tubule lumen to the epithelial cells (process: cotransport). These substances then diffuse out of the endothelial cells of the nephron tubule
and enter the interstitium. Cotransport can function with one substance going in one direction and the other
in the opposite direction. Ex. Na+ movement from higher to lower concentration
gives the energy to transport H+ from the cytosol of the nephron epithelial cells (lower concentration) to the nephron lumen (higher concentration). H+ is a basic component of urine.
o Proximal convoluted tubule is permeable to water. When the filtrate has reached the terminus of the proximal convoluted tubule about 65% of the total filtrate water has
been reabsorbed. o Henle’s loop is very permeable to water but less to most ions and urea.
At the end of this tubule an additional 15% of the initial filtrate water has been
reabsorbed by the body. Total of 80% of the filtrate water has been retain. This is called obligatory water
reabsorption.
o Now filtrate enters the ascending limp of Henle’s loop. Impermeable to water Active transport processes remove Na+, K+, and Cl-‐ from the filtrate
o The filtrate enters the distal convoluted tubule In here only the 20% of the original filtrate volume remains. The amount of volume that would be reabsorbed would be determined by the
level of antidiuretic hormone (ADH) present. The greater the amount of ADH secreted the greater the level of water
reabsorption in the distal convoluted tubule and the collecting duct.
o The concentration of urea progressively increases as the filtrate travels through the nephron tubule.
Because it is absorbed at a lower rate in comparison with water reabsorption
rate. Other substances with slow reabsorption rates are: creatinine, phosphate,
sulfates, nitrates, and urate ions.
• Concentration of Urine o When we drink a large quantity of water the kidneys will produce dilute urine. o If we consume very salt foods and/or does not drink water for an extended time
period, the kidney would produce concentrated urine. o Kidney maintains an interstitial concentration gradient of 30mOsm in the cortex and of
1200oMso in the inner medulla region. The vasa recta, urea distribution, and Henle’s
loop maintain the gradient. o Vasa recta: specialized capillaries that branch off from the efferent arterioles and
surround Henle’s loop.
When the vasa recta direct blood from the cortex to the medulla, water moves out of these capillaries and solutes move into them.
As blood flows through the vasa recta in the direction of the cortex, water
moves into these capillaries and solutes diffuse out. Vasa recta constitute a countercurrent exchange mechanism (the portion that
directs blood towards the medulla move in opposite direction to those portions
that take blood in the direction of the cortex). Using diffusion processes the vas recta contributes in the preserving of the
cortex-‐to-‐medulla solute gradient that is essential for kidney function.
o Henle’s loop functions as a countercurrent multiplier system. Filtrate progressing down through the medulla by moving through the
descending limb of Henle’s loop loses water to the interstitium via osmosis. Water then diffuses into the vasa recta that is moving blood towards the cortex.
The ascending limb of Henle’s loop is mpermeable to water. A large amount of
solutes are actively transported from the filtrate and into the medulla interstitium. (Contributes to maintaining the high solute concentration characteristics of the medulla interstitium).
o Urea also helps in the maintenance of the high solute concentration in the medulla Urea diffuses from the medulla interstitium into the descending limb of Henle’s
loop.
The ascending limb and the distal convoluted tubule are impermeable to urea, but the collecting duct is permeable.
Urea diffuses out of the collecting duct into the medulla interstitium and then
diffuses back into the descending limb. (cycled several times) • Summary of what is happening in blood filtration
o Blood in the afferent arterioles enters the glomerular capillaries.
o Components pass across the filtration barrier and enter Bowman’s space. o Blood leave the glomerular capillaries via the efferent arteriole and pass to the
peritubular capillaries and vas recta.
o Peritubular capillaries take the blood about the nephron portions that occur within the cortex and the vasa recta take the blood to the medulla
o Filtrate in Bowman’s capsule exits this structure and enters the proximal convoluted
tubule. Water is reabsorb and glucose, amino acids, Na+, Ca2+, K+, and Cl-‐ are transported out of the proximal convoluted tubule.
o Filtrate pass to the descending limb of Henle’s loop. Water enters the medulla
interstitium. o Filtrate now goes to the ascending limb of Henle’s loop. Solutes are move via active
transport processes from the nephron lumen to the interstitial fluid surrounding the
nephron. o Filtrate pass to the distal convoluted tubule and collecting duct. In the presence of
antidiuretic hormone both reabsorb more of the filtrate water.
o High solute concentration of the intertitium is needed for water reabsoprtion that occurs in the cortex and medullary regions of the kidney
Countercurrent exchange mechanism that function to maintain the solute
gradient of the cortex-‐to-‐medulla interstitium are: 1) the descending and ascending limbs of Henle’s loop, and 2) the vasa recta.
Urea also contribute in maintaining the solute gradient
• Producing a concentrated urine o ADH governs the absorption of filtrate volume from the distal convoluted tubule o How this is achieved:
In response to either a drop in blood pressure or an increase in blood plasma solute concentration, hypothalamic neurons are stimulated to generate
impulses that produce an increase in ADH secretion from the posterior pituitary.
Increase levels of secreted ADH causes:
• Insertion of additional aquaporin channels into the membrane walls of
the distal convoluted tubule and collecting duct. • Increase the permeability of the collecting duct to urea • Stimulates reabsorption of Na+ from the filtrate by the ascending limb
of Henle’s loop. Achieved by ADH-‐mediated activation of a contrasporter protein
o The filtrate that reaches the renal pelvis is properly named urine.
• Producing a dilute urine o The mechanism that causes filtrate to remain in the distal convoluted tubule and
the collecting duct are:
Increase blood volume causes increased blood pressure through the body Elevated blood pressure in the right atrium causes this chamber to secrete
atrial nitriuretic hormone
This hormone inhibits release of antidiuretic hormone (ADH) Absence of plasma ADH results in aquaporins of the distal convoluted
tubule and collecting duct becoming progressively less available. Little
water is reabsorbed. • Water conservation and blood pressure regulation via the Renin-‐Angiotensin-‐Aldosterone
Mechanism
o This mechanism involves the function of a nephron component called the juxtaglomerular apparatus.
o The macula densa cells are attached to the juxtaglomerular cells of the afferent
arteriole. The union of these two tissues constituted the juxtaglomerular apparatus.
o Its role in reabsoprtion of filtrate water is the following:
Macula desna cells senses increased blood sodium and chloride levels and respond by releasing an active vasopressor (paracine function). Vasopressor is an agent that causes a blood vessel to constrict.
Vasopressor acts upon the adjacent smooth muscle cells comprising the tunica media of the afferent arteriol. Lessened the volume of blood that enters the glomerular capillaries and glomerular filtration rate decreases.
Also causes the efferent arteriole to vasodilate (lowers glomerular capillary pressure and thus lowers GFR ebn more).
Less filtrate is form therefore there is less Na+ and Cl-‐. This decrease in Na+
and Cl-‐ is detected by the macula densa cells and they respond by upregulating activity of the enzyme nitric oxide synthase.
Upregulated activity of nitric oxide synthase stimulates production of
prostaglandins (effect: contraction of smooth muscle tissue) Prostaglandins diffuse to the juxtaglomerular/granular cells and there
activate prostaglandins-‐specific Gs receptors.
Gs receptors with bound prostaglandin send a message inside the
juxtaglomerular cell that cause the enzyme adenylate cyclase to become activated (enzyme converts ATP into cAMP
Increase levels of cAMP causes the enzyme renin to be release from the
juxtaglomerular cells. Renin catalyzes the removal of small segments from the blood protein
angiotensinogen (remove segments are termed angiotebsin I)
Angiotensin converting enzyme catalyzes the transformation of angiotensin I into angiotensin II
Angiotensin II induces arterioles and some veins to constrict (elevates
blood pressure and causes an increase in the volume of blood being return to the heart) and stmulates the release of aldosterone.
Aldosteron causes the kidney to reabsorb water as well as Na and Cl
(causes a decrease in urine production and thus conservation of water) • Autoregulation of Glomerular filtration rate/ GFR
o By regulating the contractile state of the tunica media tissue layer in the afferent
and/or efferent arteriole, the kidney can largely self-‐regulate GFR. • Sympathetic innervation of the kidney
o Causes a decrease in filtrate formation as a consequence of vasoconstriction of
the afferent arterioles as well as small arteries in the kidney. (regulated by norepinephrine)
• Voiding urine from the body
o A hydrostatic pressure of 18mmHg in Bowman’s capsule favores the movement of filtrate to the renal pelvis (pressure of 0mmHg). The smooth muscles create peristaltic waves that move the urine from the renal pelvis to the bladder.
o Micturition: process that causes the smooth muscles of the urinary bladder wall to contract in response to stretching of this organ. Contraction moves the urine out of the bladder.
o The stretch response is initiated by stretch receptors in the urinary bladder. Sends messages to the sacral region of the spinal cord along pelvic nerves. The message pass to the higher brain centers that cause one to have a conscious urge to
urinate. Parasympathetic efferent nerves fibers convey these messages to the urinary bladder. These cause the smooth muscle of the bladder to contract and the urinary sphincter to relax. Urine is thus voided from the body.
Chapter XV: The Respiratory System
• Air is drawn into the lungs so that oxygen can diffuse into the capillaries and carbon dioxide can diffuses into the lungs.
Anatomical and Histologial Features of the Respiratory System
• Major Organs: o Oral Cavity o Upper Respiratory Tract
Nasal Cavity: • Nose: prominent feature on the face through which air enters the
nasal cavity o Cartilaginous plates occupy the main portion of the
external nose. o Bridge is made up of nasal bones and potrusions of the
frontal maxillary bones. o Nasal cavity occurs within the external nose.
extends and merges with the pharynx o Nares/Nostrils: outside openings to the nasal cavity o Internal Nares: inside openings of the nasal cavity to the
pharynx • Vestibule: area inside the external nares
o lines with stratified squamous epithelium that merges with the skin
o Mucous Membrane: pseudostratifies columnar epithelium Mucus is produced by goblet cells. Hairs lining the vestibule trap dust particles Cilia sweep the mucus containing dust particles
down the throat • Olfactory Epithelium: confers the sense of smell, located in the
superior portion of the nasal cavity. • Nasal Septum: divides the nasal cavity into two halves. • Hard Palate: floor of the nasal cavity composed of bone covered in
mucosa • Conchae: three bony ridges that are alterations to each lateral
wall of the nasal cavity • Meatus: air passageway occurring within each concha
Pharynx/Throat: • Entrance for respiratory and digestive systems, continuos with the
nasal cavity and with the respiratory system at the larynx. • Three components:
o Nasopharynx: upper portion that extend from the internal nares to the uvula. Has a mucous membrane lining, pharyngeal tonsil protects against infection in the posterior region of the nasopharynx.
o Oropharynx: from uvula to epiglottis (mucous covered membrane-‐covered cartilage that covers the glottis of the larynx when swallowing occurs. Oral cavity opens into it via the fauces. Protects against abrasion by presence of a layer of stratified squamous epithelium.
o Laryngopharynx: from terminus of the epiglottis to the larynx and esophageal openings; stratified squamous epithelium lines this structure.
o Lower Respiratory Tract Larynx
• voice box • Made up of cartilages (six paired, three unpaired) joined to one
another by muscles and ligaments. o Adam’s apple is the largest. o Cricoid: interior most o Epiglottis: third unpaired
Elastic properties enable it to flex and cover the larynx while swallowing.
• Two ligament pairs extend from the arythenoid cartilages to the thyroid cartilage.
o The superior one establishes vestibular folds/false vocal chords; come together during swallowing to prevent material from entering the larynx and also to keep air in the lungs while holding your breath..
o The inferior one (vocal ligament) establishes the vocal folds/true vocal chords.
o Glottis: true vocal chords and the space between them. • Vestibular folds and the vocal chords are covered with stratifie
swuamous epithelium the remainder of the larynx is covered with pseudostratified ciliated columnar epithelium.
• Speech: vibration of the vocal chords resulting from air moving past them.
o Changes in pitch: altering the length of the true vocal chords, changing the frequency at which they change.
o Changes in volume: grater volume corresponds to greater amplitude
• Laryngitis: inflammation of the mucosal epithelium of the vocal chords.
Trachea/Windpipe: • comprised of 15-‐20 cartilaginous rings surrounded by smooth
muscle and connective tissue. o prevent the trachea from collapsing
• Interior surface is covered with pseudostrtified ciliated columnar epithelium and goblet cells.
• Mucus is moved by the cilia in the direction of the larynx, enabling it to enter the esophagus and be swallowed.
Bronchi • Primary Bronchi: extend from the terminus of the trachea to the
lungs; right and left primary bronchi o right one is shorter and greater in diameter o inner surface is covered in pseudostratified ciliated
columnar epithelium and regularly spaced cartilaginous rings.
Lungs • Organs of the body that deliver the ntrient oxygen to the blood
and receive the waste product carbon dioxide from the blood. • Two lungs contained in either the left of right lteral portion of the
thoracic cavity • Approximately conical elongated shape • Base rests upon the diaphragm (skeletal muscle that separates the
thoracic cavity from the abdominal cavity). • Superior-‐most part is one inch above the clavicle. • Right lung 11% greater mass than the left lung, comprised of three
lobes, made up of 10 lobules. • Left lung comprised of two lobes, made up of 9 lobules. • Each lobe is divided into lobules separated from one another via
connective tissue. • Each primary bronchus branches into secondary bronchi. • Hilum: point of bronchus entry into the lung. • Secondary bronchi branch into tertiary bronchi, which convey air
into each lobule, further, branching lead to the bronchioles. • Bronchioles: smallest air passageways of the lungs. Are 1mm or
less in diameter. o Larger ones are lined on the inside with ciliated simple
columnar epithelium o Smaller ones simple squamous epithelium surrounded by
elastic connective tissue. o surrounded by smooth muscle which can constrict to
block air flow. Continued constriction can cause asthma. • Continued branching of the bronchioles eventually result in
formation of therminal bronchioles/lobular bronchioles which branch into respiratory bronchioles which branch into alveolar ducts that lead to hollow air sacs called alveoli.
• Simple squamous epithelium makes up the walls o the smaller bronchioles, alveolar ducts and alveoli.
o Elastic connective tissue surrounds these walls. • Alveolar walls: contain secretory cells that secrete a lipoprotein
substance called surfactant that prevents the alveoli from collapsing during exhalation.
o Macrophages in the inner surface maintain the area free of foreing material facilitating efficient gas exchange.
Protective Tissues Surrounding the Lungs and Lining the thoracic Cavity
• Pleura: protect the lungs • Parietal Pleura: lines the inner thoracic wall • Pulmonary Pleura/Viceral Pleura: covers the lung • Both Pleura transition into one another at the lung hilum. • The pleural cavity, between both layers, is filled with pleural fluid.
o During inspiration and expiration it reduces abrasion (that happens when the lungs expand and contract) between the two pleural membranes.
o It maintains both membranes in contact so they can slide past one another.
Bringing Blood to the Lungs
• The lung tissue must receive oxygen-‐enriched blood to support their own metabolic needs as well.
• The thoracic aorta forms a branch called the bronchial artery that directs oxygen-‐enriched systemic blood to the lungs.
o branches of this vessel bring blood to all tissues including the bronchi nad bronchioles.
• Blood is directed back to the heart via the bronchial veins and becomes mixed with a larger volume of blood that has just been oxygenated within the capillaries surrounding the alveoli, bronchial veins merge into the pulmonary veins. This results in a minor reduction of oxygen in the blood in the pulmonary veins.
Muscle Used in Respiration
• Inhalation: contraction of the diaphragm and the external intercostal muscles that cause air to be drawn in.
• Expiration: Relaxation of these muscles then moves the air out. • Energy, that is needed for contraction, is required for breathing to occur. • Diaphragm: dome of skeletal muscle tissue, when relaxed arches up into the thoracic
cavity. contraction of this muscle enlarges the thoracic cavity. • The external intercostal muscle contract and rotate the ribs upwards and pushes the
sternum away from the spinal column. It also increases the size of the thoracic cavity and thus the lungs.
• Contraction of the Internal intercostal muscles underlies expiration.
Inspiration and Expiration
• Boyle’s Law (General Gas Law): or a given, fixed volume quantity of gas molecules held at constant temperature, there is an inverse relationship between volume and pressure. [P=1/V]
o At a grater volume, a fixed quantity of gas molecules at constant temperature will produce fewer collisions with the sides of a container per unit time than they would in a smaller container, thus reducing pressure.
• Dalton’s Law (Partial Pressure of Gasses Law): for a given gas mixture at constant temperature and a fixed number of molecules, the partial pressure of each molecular species comprising the gas mixture is directly proportional to the percentage of the gas mixture that is made up of that species multiplied by the total pressure of the gas mixture. [PT= P1 + P2]
o For oxygen to move from the alveolar space into the blood and CO2 to move from the blood to the alveolar space it is required that the partial pressure of each gas is maintained higher in the area from which it is diffusing and lower in the area it is diffusing to.
• Henry’s Law: the amount of gas that will be absorbed into a liquid at a given temperature is almost directly proportional to the partial pressure of that gas.
o Although a gas species at a higher partial pressure will more readily diffuse into a liquid, different gas molecular species exhibit differences in their capacities to become solubilized in the first place.
• Contraction of muscles will increase the thoracic cavity volume and thus lung volume. This will decrease the pressure in the lungs . Since fluids flow from areas of greater to lower pressure through bulk flow, air will move into the lungs.
• Since the lungs are surrounded by the pulmonary pleura and this layer adheres to the parietal pleura when the thoracic cavity changes in volume the lungs will do the same.
• Air ceases to move in or out of the lungs when pressure differences between the air within these organs is equal to atmospheric pressure. Only 1mm Hg difference is needed for efficient respiration to occur.
• Resistance to air flow is usually minimal but may increase when mucus builds up in the lungs or the bronchioles constrict (asthmatic attack).
• Lungs can collapse as a result of either recoil of elastic fibers contained in the alveolar walls or as a consequence of change in the surface tension of the very thin fluid layer on the inner surface of the alveoli.
Compliance
• Degree to which lungs and thorax can change in volume as a function of intrapulmonary pressure is referred to as compliance.
• Expressed as liters (volume of air) per cm of water (pressure). • Average: 0.13/cmH2O • Greater compliance values correlate with greater ease in lung and thoracic volume
expansions. Lung Volume and Lung Capacity
• Spirometer: device that measures the amount of air that can be moved into and out of the lungs
• Spirometry can determine the following (aspects of the volume of air that is inspired) o Tidal Volume: amount of air moved during one cycle of breathing at rest (0.5L) o Inspiratory Reserve Volume: amount of air that can be forcefully inspired after a
normal inspiration (3L) o Expiratory Reserve Volume: amount of air that can be forcefully expired after a
normal exhalation. (1.1L) o Residual Volume: air volume remaining in the lungs after forceful exhalation (1.2L)
• Lun Capacities: o Inspiratory Capacity: tidal volume + Inspiratory Reserve Volume (3.5L) o Functional residual Capacity: Expiratory Reserve volume + residual volume (2.3L) o Vital Capacity: inspiratory reserve volume + tidal colume + expiratory reserve
volume (4.6L) o Total Lung capacity: inspiratory reserve volume + tidal volume + expiratory reserve
volume + residual volume (5.8L)
Gas Exchange: Applications of Dalton’s and Henry’s Law to Respiration
• Gas molecules are in constant random motion, this and the tendency of the universe to proceed towards greater disorder will cause gas molecules to move from areas of greater to lower concentration.
o Oxigen will difuse from the alveolar air space to the capillary plasma; from a gaseous to a liquid state
o Carbon dioxide will move from the capillary plasma to the alveolar space; from a liquid to a gaseous state
• Partial Pressure contributed by water in alveolar and humid air reduce the partial pressures contributes by the other air molecules.
o water comes from the moist environment within the lung air passageways and alveoli; water molecules thus evaporate as air passes through the lung passageways; the percentage fo these other air molecules are reduced.
• CO2 also contributes a significant amount of the partial pressure to alveolar air and further reduces the partial pressures of the other air molecular components.
• Gas molecules that are in contact with a liquid tend to diffuse into that liquid. Degree to which this occurs depends:
o Partial pressure of the diffusing gas molecule o Solubility of the particular gas molecule within the liquid
• Henry’s Law: concentration of a dissolved gas is equal to the partial pressure of that gas multiplied times the solubility coefficient [p=kHc]
• Solubility coefficients: o O2=0.024, 24mL/Lwater o CO2=0.57, 570mL/Lwater o N2=0.012, 12mL/Lwater
• Gases have a partial pressure of zero when dissolved in a liquid. • Respiratory membrane is 0.5 mm thick, consists of six components;
o film of fluid occurring on the inner alveolar surface o alveolar epithelium o alveolar basement membrane o interstitial fluid separating the alveolus from the immediately adjacent capillary o capillary basement membrane o capillary endothelium
• How a particular gas diffuses across the membrane is a function of: o respiratory membrane thickness o diffusion coefficient for the particular gas species (higher more diffusion) o membrane surface area o difference in partial pressure for the gas
• Partial pressure of oxygen is 104mm Hg in the alveolar air space but only 40mm Hg in the blood plasma.
• Pco2 difference is only 5mm Hg but CO2 has a very high diffusion coefficient enabling it to leave the blood in enough quantities.
• Many respiratory illnesses manifest themselves by affecting oxygen and carbon dioxide partial pressures.
• Diffusion of oxygen into capillaries continues until the plasma Po2 reaches 104 mm Hg. By the time the blood is leaving the lungs it’s Po2 has decreased to 95 mm Hg this resulting from the mixing with the oxygen depleted blood form the bronchial veins. Po2 within intersitial fluid, 40 mm Hg and intracellular Po2 is 20 mm Hg. Oxygen diffuses down this gradient where it is metabolically needed.
The Role of Hemoglobin in Blood via Oxygen Transport
• When plasma Po2 is above 80 mm Hg all hemoglobin molecules are saturated with oxygen. • When Po2 has fallen to 40 mm Hg hemoglobin molecules are still 75% saturated with
oxygen. • Strenous exercise causes Po2 to be 15 mm Hg and only 25% of the hemoglobin molecules
to be saturated with oxygen. • There is a non-‐linear relationship between Po2 values and the tendency of oxygen to
dissociate from hemoglobin. o Curve is steepest at Po2 ranging from 15-‐35 mm Hg o Above Po2 40 mm Hg oxygen dissociates from hemoglobin at a much slower rate.
Oxygen-‐Hemoglobin Binding is affected by Po2 values, Temperature, and pH
• CO2 can be carried in the blood as: o dissolved gas in blood plasma (8%) o bound to hemoglobin (carbaminohemoglobin : 20%) o bicarbonate/HCO3
-‐ (72%) • Enzyme carbonic anhydrase converts carbon dioxide and water into carbonic acid which is
a weak acid tha loses its proton to form bicarbonate. • Bohr Effect: As carbon dioxide levels increase in the blood it accumulates and grater
quantities of carbonic acid are produced. When it dissociates the increased [H+] causes the pH to decrease and this pH alters the hemoglobin conformation to release Oxygen.
• Chloride Shift: movement of chloride into the erithrocyte through an antiport protein that removes accumulated bicarbonate from the cell.
• The hydrogen ions bind to hemoglobin and when the hemoglobin becomes saturated it then releases the protons so that the plasma pH does not drop significantly.
• When plasma is in the capillaries that surround the alveoli the process is reversed and the pH increases slightly.
• As temperature increases more oxygen disassociates dorm the hemoglobin molecules.
Respiratory Regulation:
• Respiratory Center: located in the medulla oblongata. consists of inspiratory and expiratory components.
o inspiratory center: two groups of nuclei that occur bilaterally within the dorsal portion of the medulla oblongata
neurons are spontaneously stimulated and send action potentials along the reticulospinal tracts, emerge within phrenic and intercostal nerves (cause the diaphragm and external intercostal muscles to contract).
o Expiratory Center: comprised of two nuclei occurring bilaterally. not active during quiet respiration (16-‐18 inhalations per minute).
During heavy breathing it becomes regularly active sending action potentials along nerves along nerves that innervate muscles of expiration.
o Unidentified mechanism links both centers so that when inspiratory becomes more active, expiratory is activated.
• Apneustic Center: of the pons sends regular stimulatory messages to the inspiratory center. Ensuring that inspiration occurs rhythmically.
• Pneumotaxic Center: aggregation of neurons that down regulate the inspiratory and apneustic centers
• During strenuous physical exertion the Hering-‐Breuer reflex prevents the lungs from over-‐inflating. Afferent nerves convey messages along the vagus nerve inhibiting the inspiratory center.
• Rate of breathing can be consciously regulated via input from the cerebral cortex.
The Digestive System
• Metabolism o Total sum of chemical reactions require to sustain life o Basic biomolecular nutrients needed include amino acids, lipids, carbohydrates, and
nucleic acid, water and ions. o The digestive system provides these nutrients.
• Digestive tract organs and functions
o Mouth/Oral cavity Food enters the digestive tract here Leads to the pharynx
Accessory organs: salivary glands and tonsils o Pharynx/throat
Takes food from the oral cavity to the esophagus
Accessory components: mucous glands o Esophagus
Takes food from the pharynx to the stomach.
Cardiac sphincter controls the entrance of food to the stomach Accessory components: mucous glands
o Stomach
Function: stores ingested food and converts it into a liquefied form (chyme) Pyloric sphincter controls the chyme pass to the small intestine. The chemical breakdown begins here
o Small intestine Function: nutrient absorption Made of 3 regions: duodenum, jejunum, and ileum
o Large intestine/colon Salt and water absorption Chyme that has not been absorbed is processed into feces.
Accessory organs: mucus-‐secreting glands o Rectum
Final portion of the digestive tract
Terminal portion of the rectum is the anus. • Digestive tract histology Four mayor tissue layers (mucosa, serosa, submucosa, and muscularis)
o Mucosa (3 layers) Mucous epithelium
Moist stratified columnar epithelium in the mouth, oropharynx, esophagus, and anus.
Simple columnar epithelium in other regions of the digestive tract.
Lamina propia
Loose connective tissue Muscularis mucosae
Smooth muscle layer
o Submucosa Connective tissue layer beneath the mucosa Nerves here establish the submucosal plexus (under parasympathetic control)
o Muscularis Inner layer of smooth muscle that encircles the digestive tract along with
longitudinally arrange smooth muscle.
Myenteric plexus: parasympathetic cell bodies and nerve fibers (occur between the circular and longitudinal smooth muscle layers.
The submucosal plexus and myenteric plexus form the intramural plexus
(regulates muscle contraction and secretion of substances) o Serosa/adventitia (visceral peritoneum)
Thin layer of connective tissue and simple squamous epithelium.
o Tree mayor glands associated with the digestive tract Unicellular mucous glands of the mucosa Multicellular glands of the mucosa and submucosa
Multicellular glands occurring outside of the digestive tract • Digestive Physiology
o Ingestion: act of bringing food into the stomach portion of the digestive tract
Food first enters the mouth where solid food is masticated (most important of mechanical digestion)
Mouth arranges food being masticated in bolus. This bolus is then pushed into
the esophagus. (movement of the food to the stomach Is thanks to peristaltic contractions)
Liquefied food in stomach and small intestine needs to be mixed (mixing
possible through muscle contraction of the tunica muscularis During the trajectory of food trough the digestive tract substances are added to
the food or the tract walls.
Mucus produce by secretory cells lubricate food and the digestive tract (this facilitate food’s passage)
Enzymes and digestion-‐promoting chemical agents are added (important in
chemical digestion) Water is added to ingested food
o Digestion: breakdown of large food molecules into their smaller constituent
components. Adsorption of these breakdown products delivers them to the circulatory
system. Unabsorbed materials are voided from the body via elimination
Digestive tract anatomical features and functions • Mouth/oral cavity
o Form Divides in 2 basic components: vestibule and oral cavity proper (located
between the alveolar process)
Boundaries: lips, fauces, palate and cheeks. Uvula: hangs down from the posterior edge of the soft palate Tongue: muscle that makes the majority of the oral cavity. Taste buds identify
flavors. Teeth: 32 that occur in two dental arches Palatine tonsil: occur in lateral wall of fuces
Salivary gland: 3 types (Parotid glands, Submandibular glands, and Sublingual glands)
Jaw muscles: cause the teeth to move
o Function Lips and cheeks maintain and manipulate food in the oral cavity Manipulates food
Teeth: masticate food Muscle: move jaw and teeth for mastication Salivary glands: secrete saliva, helps chewed food to be held together and
formed into a bolus, and initiates carbohydrate digestion. • Pharynx/throat (divides into 3 components)
o Nasopharynx: located above the soft palate
o Oropharynx: located behind the oral cavity o Laryngopharynx: occurs posterior to the larynx o Function:
Serves as the opening to the esophagus and the windpipe • Esophagus
o Occurs between the pharynx and the stomach
o Lower esophageal sphincter regulates passage of food from the pharynx to the esophagus.
o Located behind the trachea but in front of the vertebrae
o Mucosal lining: made up of moist stratified squamous epithelium o Glands secrete mucus that lubricate the esophagus o Esophageal hiatus: opening in he diaphragm that allows the sophagous to pass from the
thoracic cavity into the abdominal cavity o Cardiac sphincter/lower esophageal sphincter: area were the esophagus joins the
stomach o Superior region comprise of skeletal muscle and the final region is only smooth muscle. o Function
Moves food from the pharynx to the stomach
Peristaltic contractions (moves food): circular muscles surrounding the esophagus initiate the contraction at the upper esophageal sphincter region.
• Stomach
o Occur in the superior abdominal region o Fundus: located to the let of and superior to the cardiac sphinter o Body: largest portion of the stomach. The upper portion has the lesser curvature and the
lower portion the greater curvature. o Pyloric region: truncates and form the pyloric sphincter that controls the flow of food
from the stomach to the duodenum (compose of a layer of thick smooth muscle)
o Stomach tissues Serosa tissue: inner portion = connective tissue and the outer = simple squamous
epithelium
Muscularis (3 layers): longitudinal (outer), circular (middle) and oblique (inner) Mucosa and submucosa: rugae = large folds in this tissue that enable the stomach
to expand
o Stomach mucosa Gastic pit: tube like structures 5 forms of epithelia cells make the stomach mucosa
Surface mucous cells: secrete mucus onto the stomach surface Mucous neck cells: produce mucus Parietal cells: produce hydrochloric acid and intrinsic factor
Chief cells: produce the inactive precursor to the proteolytic enzyme pepsin
Endocrine cells: produce gastrin (hormone) that induces hydrochloric acid
to be secreted o Functions:
Ingested food is mixed with water such that it becomes liquefied into chime
Protein digestion thanks to the proteolytic enzyme pepsin 3 phases of stomach secretion regulation
Cephalic phase: gustatory and olfactory receptors perceive food molecules
-‐ centers in the medulla send messages along efferent parasympathetic nerve fibers – cholinergic postganglionic receptors cause cells of the stomach mucosa to secrete substances
Hydrochloric acid: lowers pH of stomach (denatures protein and kills ingested microorganisms
Gastrin: induce release of hydrochloric acid. Secreted by
endocrine cells (transported by circulatory system until it reaches the target cells)
Intrinsic factors: instruct ileum to uptake vitamine B12 (require for red blood cell production)
Pepsinogen: inactive precursor to the proteolytic enzyme pepsin
Gastric phase: stomach secretion (high level). Phase is induce by
Stomach distension: activates stomach mechanoreceptors Amino acids and short amino acid sequence within the stomach:
stimulates parietal cell secretion of hydrochloric acid
Intestinal phase: mediated through the entrance of the acidic chyme into the duodenum.
pH of chyme is below 3 the intestine sends inhibitory messages
that halt further gastric secretion (result from secretion of secretin by the duodenum)
pH of chyme is above 3 the intestine sends stimulatory messages
which induce further gastric secretion cholecystokinin (hormone) and gastric inhibitory peptide are
release from the duodenum and the jejunum in response to fatty
acids and other lipid substances. Both inhibit gastrin secretion. Enterogastric reflex: inhibition of gastrin release
o The pressure in the stomach only increases when it becomes almost full to capacity.
o Pyloric pump: peristaltic contractions that move chyme through the partially constricted pyloric opening.
o The content of the stomach can’t be emptied too rapidly – result in less nutrient
absorption in the small intestine. o Food too much time in the stomach becomes very acidic and could damage the stomach
wall.
• Small intestine o Function: chemically breakdown large food molecules into biomolecules that cn be
absorb across the epithelium.
o Accessory glands/organs: liver and pancreas o Made up of 3 sections
Duodenum
o Joins to the right inferior portion of the stomach at the pyloric region o Greater duodenal papillae: the common bile duct and pancreatic duct merge to establish
the hepatopancreatic ampulla (ampulla of Vater). The hepatopancreatic ampulla sphincter
is a ring of smooth muscle that maintains the ampulla of Vater close. The absorptive surface area is increase through all of the:
Circular folds: ringed-‐structures, localize in the mucosa and submucosa
tunic layers Villi: extensions of the duodenum mucosa that project into the lumen.
Contains blood capillaries and a lymph capillary (lacteal)
Brush border: simple columnar epithelial cells. Formed the microvilli o lesser duodenal papillae
o 4 types of cells comprise the mucosa of the duodenum Containing microvilli: produce and secrete digestive enzymes, also absorb
substances
Goblet cells: generate and secrete mucus
Granular cells: produce antibacterial proteins and protect the duodenum Endocrine cells: produce and secrete hormones
o Crypts of Lieberkühn: glands where the new mucosa epithelial cells are located
Goblet and absorptive cells migrate from the crypts of Lieberkuhn to the portion of the villus that projects farthest into the lumen of the duodenum.
Jejunum and Ileum
o Most absorption of nutrients occurs in the duodenum and jejunum o Ileocecal sphincter: smooth muscle surrounding where the jejunum joins to the ileum. Halt
or allow the passage of chyme
Small Intestine Functions o Primary organ of nutrient absorption o Mucosa layer secrete
Mucus: secreted by duodenal glands, intestinal glands and goblet cells. Protects the wall from very acidic chyme
Electrolytes
Water o secretion from the liver and pancreas enters the small intestine (include enzymes needed
to enable chemical digestion). Secreted in response to 2 hormones (secretin and
cholecystokinin) o bili from the liver emulsifies fats and facilitates their breakdown into biomolecules o movement of chyme
segmental and peristaltic contractions move the chyme 3-‐5 hours are require for food to move through the small intestine Mechanical and chemical stimuli stimulate these muscles to contract. Also
stimulate the associated parasympathetic plexuses. Example: Intestinal wall distension Chyme that is hyper-‐ or hypotonic
Chyme having low pH Products of chemical digestion, including amino acids and peptides
o Peristaltic contractions cause the ileocecal sphincter to open and food passes from the
jejunum to the ileum o Absorption of nutrients from the chyme
9 l/per day enters the small intestine almost everything is reabsorb
Water, ions, and water-‐soluble products of digestion are absorb into the hepatic portal system
Products of lipid metabolism
o Carbohydrates digestion Complex carbohydrates are chemically broken down so the products may be
absorb o Lipid digestion
Mostly hydrophobic. Lipid molecules cluster together in the presence of water,
this make them inaccessible to digestive enzymes. Bili slats function to emulsify the large lipid droplets into micelles (lipid
monolayers). This makes all the lipid molecules available to lipase.
Resulting product is absorbed across the mucosal epithelium Simple diffusion: brings the products of lipid digestion inside the cell
o Protein digestion
Enzymes that breakdown proteins (proteases) Pepsin: secreted by the stomach Trypsin, chymotrypsin, carboxypeptidase, and elastase: produce by the
pancreas Complete digestion results in tripeptides, dipeptides, and amino acids Amino acids are passed on to the blood within villi capillaries that then directs
them to the hepatic portal system Growth hormone and insulin instruct cells to uptake amino acids.
o Water and absoption
92% of the water is reabsorbed by the small intestine and 6-‐7% is absorbed by the large intestine
Osmotic gradients determine whether water moves into or out of the small
intestine o Ion absorption o Epithelial mucosa cells utilizes active transport mechanisms to acquire ions from the
chyme (Na+, K+, Ca2+, Mg2+, and PO42-‐)
Vitamine D, parathormone, and calcitonin influence Ca2+ absorption Cl-‐ flows via passive movement
• Liver o Porta: point of entry or exit for the blood vessels, lymphatic vessels, ducts, and nerves o Hepatic portal vein: drains blood from the gastrointestinal tract and pancreas to the liver
o Hepatic artery: delivers blood to the liver, gall bladder, pancreas, stomach, and duodenal portion of the small intestine
o Hepatic artery proper: branch of common hepatic artery that runs alongside the portal
vein and common bile duct. (3 structures form the hepatic triad) o Common hepatic duct: form from the convergence of
Right hepatic duct: drain bile from right lobe of liver
Left hepatic duct: drain bile from the left lobe of the liver Cystic duct: joins the gall bladder to the common bile duct
o Hepatocytes: liver cells that remove glucose, amino acids and other nutrients and store
glucose, fat, and vitamins (A, B12, D, E, and K) • Liver histology
o Liver surface Covered in connective tissue and peritoneum Bare areas: portion of the liver’s surface that lack peritoneum
Septa: function to divide the liver (divisions lobules) and provide support
Each lobule has a central vein that drains the lobule. The 4 central veins unite to form hepatic veins (direct blood from the posterior and superior liver surface to the inferior vena cava.
Hepatic cords: mass of cells that form columns and plates. Made up of hepatocytes.
Hepatic sinusoids: space between both hepatic cords and blood channels
• Hepatocytes roles: o Bile production o Biotransformation
o Storage o Production of blood components
• Hepatocytes take up nutrients from the arteries and venous systemic blood
o Oxygen, amino acids, simple sugars, and nucleic acids. o Hepatocyte-‐produce blood components are secreted into the hepatic sinusoids or the bile
canaliculi.
o Blood in the hepatic sinusoids pass to the central vein and then to hepatic veins that takes the blood out of the liver and into the inferior vena cava
o Mixing of oxygen-‐rich and oxygen-‐poor blood is necessary because oxygen from the
hepatic arteries provides the hepatocytes with the capacity to generate ATP energy (require for active transport)
o Bile (made of water and bile salts and metabolic byproducts): moves through bile
canalicilu to the hepatic triad and then exists the liver by moving through the hepatic ducts.
• Functions of the Liver
o Bile production Bile (contains bicarbonate) entering the duodenum protects this portion from the
acidic chyme.
Bile salts function to emulsify fats and facilitate chemical digestion Bilirubin: product of hemoglobin degradation
o Regulation of bile secretion
Involves parasympathetic stimulation Bile salts increased bile secretion (positive feedback mechanism)
o Storage
Simple sugars: glucose that will be incorporated into glycogen Amico acids, fat and fat related substances, Vitamins (A,B12,D,E, and K), Cu+2, and
Fe2+
o Interconversion of nutrients o Detoxification
Toxic substances are modified so they become less toxic or nontoxic Ammonia is converted into urea
o Phagocytosis
Kupffer cells remove dead and dying red and with cells. Bacteria can also be
removed. o Synthesis
Albumin, fibrinogen, globuline, heparin and blood clotting factors.
• Gall bladder o Receives bile from the liver via the cystic duct o Absorbs water and electrolytes
o Cholecystokinin causes smooth cell of the gall bladder to contract, causing the release of bile into the cystic duct
• Pancreas
o Produces digestive juices-‐ secreted via exocrine processes o Juices consists of:
Aqueous components generated by columnar epithelial cells. Na+ and K+
concentrations are similar to those of extracellular fluids. Bicarbonate is in high concentrations (functions to neutralize chyme that enters the small intestine, this increase pH that abolish pepsin activity and promote activity of digestive enzymes)
Digestive enzyme components: produced by acinar cells. There are 4 pancreatic digestive enzymes
Proteases: breakdown proteins. Secreted as inactive form (zymogens)
Trypsin: enzyme enterokinase converts trypsinogen into the active form
Chymotrypsin
Carboxypeptidase Amylase: break down complex carbohydrates Lipases: break down lipids
Deoxyribonucleases and ribonucleases: break down DNA and RNA • Regulation of Pancreas Exocrine function
o Nervous and endocrine mechanisms regulate release of pancreatic juices.
Parasympathetic innervation stimulates release of digestive juice rich in digestive enzymes.
o Secretin causes a bicarbonate-‐rich, aqueous digestive juice to be form.
o Cholecystokinin: release in response to the presence of amino acids and fatty acids in the small intestine lumen. Causes bile and pancreatic juice (enzyme-‐enriched) secretion.
• Large Intestine o Chyme requires 18-‐24 hours to pass through the large intestine or colon. o Goblet cells secrete the mucus that lubricates the epithelial surface and causes the
fecal matter to aggregate. o Feces are made up of water, undigested food, microorganism, and epithelial cells.
o Flatus results from symbiotic bacteria converting certain molecules in methane and hydrogen gases.
o Chyme progress through the large intestine thanks to peristaltic waves. Peristaltic
contractions result in mass movements, which occur 3-‐4 times a day. o Defecation reflex is initiated in response to distension of the rectal wall caused by
feces moving through the rectum. These stretch messages cause parasympathetic
reflexes to stimulate strong rectal contractions that causes defecation. o Large intestine consists of: cecum, ascending colon, traverse colon, descending colon,
and sigmoid colon.