Inquiry into LifeTwelfth Edition

Chapter 14

Lecture PowerPoint to accompany

Sylvia S. Mader

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

14.1 The Digestive Tract

• Functions

– Ingest food

– Digest food to

nutrients

– Absorb nutrients

– Eliminate indigestible

remains

14.1 The Digestive Tract

• Digestion– Mechanical

• Large piece of food become smaller ones• Chewing of food in the mouth• Churning and mixing of food in the stomach

– Chemical• Enzymes break down macromolecules into smaller

molecules that can be absorbed

14.1 The Digestive Tract

• The Mouth– The Tongue

• Comprised of skeletal muscles

• Taste buds

– Roof• Hard palate (anterior)

– Contains several bones

• Soft palate (posterior)– Made of muscle

– Uvula: A finger shaped projection at the back of the mouth

– Tonsils: Help protect the body from infections

14.1 The Digestive Tract

• The Mouth– Salivary Glands

• Three pairs of glands that send saliva through ducts to the mouth

• Saliva contains salivary amylase that begins digesting starch.

14.1 The Digestive Tract

• The Teeth– 20 baby teeth– 32 adult teeth– Two divisions of a tooth

• Crown– Enamel– Dentin– Pulp

• Root– Dentin– Pulp

14.1 The Digestive Tract

• Pharynx– Receives air from the nasal cavities and food from the

mouth

– Swallowing• A reflex action• Soft palate closes off the nasopharynx• Trachea moves up causing the epiglottis to cover the glottis

Swallowing

14.1 The Digestive Tract

• Esophagus– A muscular tube that extends from the pharynx to the stomach

– The esophagus is usually collapsed except during swallowing

– Peristalsis (rhythmic contractions) pushes food along the digestive tract

– A sphincter muscle closes the esophagus from the stomach

– Relaxation of the sphincter allows food to enter the stomach

– If contents of the stomach escape into the esophagus, this cause heartburn.

14.1 The Digestive Tract

• The Wall of the Digestive Tract– Mucosa

• Epithelium supported by connective tissue and smooth muscle

• Lines lumen• Glandular epithelial cells produce enzymes• Goblet cells produce mucus

– Submucosa• Loose connective tissue• Contains blood vessels and lymph nodules• Lymph nodules are present

14.1 The Digestive Tract

• The Wall of the Digestive Tract– Muscularis-

• Two layers of smooth muscle– Longitudinal, outer layer runs along length of gut– Circular, inner layer encircles tube

– Serosa• Squamous epithelium• Supported by connective tissue• Secretes serous fluid

Wall of the Digestive Tract

14.1 The Digestive Tract

• The Stomach

– Receives food from the esophagus

– Moves food into the small intestine

– Can expand to hold about 4 liters

14.1 The Digestive Tract

• The Stomach– Both mechanical and chemical digestion occur in the

stomach.– The stomach wall has three layers of muscles that

churns the food, mixing it with gastric juices.– Gastric glands in the lining of the stomach secretes

pepsinogen, HCl, and mucus.• Pepsinogen is converted to pepsin

– Mucus protects the wall of the stomach from the HCl.• An ulcer may develop if HCL penetrates the mucus.

Anatomy and Histology of the Stomach

14.1 The Digestive Tract

• The Small Intestine– Approximately 6 meters long but smaller in diameter

compared to the large intestine

– Duodenum• The first 25 centimeters of the small intestine• Receives bile from the liver

– Bile emulsifies fat

• Also receives pancreatic juice from the pancreas– Many enzymes for digestion of nutrients– Bicarbonate to neutralize pH

14.1 The Digestive Tract

• Villi and microvilli increases the surface area of the small intestine

• Villi contains:– Blood capillaries for

nutrient absorption– Lacteals (lymph

capillaries)

14.1 The Digestive Tract

• The Large Intestine – Approximately 1.5 meters long but larger in diameter compared

to the large intestine

– Absorbs water, salts, and some vitamins

– Stores indigestible materials until it can be eliminated

– Includes the cecum, the colon, the rectum, and the anal canal

Junction of the Small Intestine and the Large Intestine

Defecation Reflex

14.2 Three Accessory Organs

• The Pancreas• The Liver• The Gallbladder

14.2 Three Accessory Organs

• The Pancreas

– Endocrine function• Insulin and glucagon

• Regulate blood glucose

– Exocrine function• Sodium bicarbonate

• Pancreatic amylase: starch digestion

• Trypsin: protein digestion

• Lipase: fat digestion

14.2 Three Accessory Organs

• The Liver– Largest gland in the body– Lobules are the structural and functional units

• Triads– Located in lobules

» A bile duct» A branch of the hepatic artery» A branch of the hepatic portal vein

• Detoxifies poisonous substances in blood• Removes and stores iron and vit. A, D, E, K, and B12

• Makes plasma proteins• Regulates cholesterol

14.2 Three Accessory Organs

• The Liver – Glucose regulation

• Excess glucose stored as glycogen in the liver• Glycogen broken down to glucose when needed• When glycogen is depleted

– Converts fats and amino acids to glucose

– Requires deamination of amino acids

» Liver combines ammonia with carbon dioxide

» Forms urea

Hepatic Lobules

14.2 Three Accessory Organs

• The Liver – Bile production

• Stored in gallbladder• Composition

– Bilirubin

» From breakdown of hemoglobin

» Greenish color

– Bile salts

» Derived from cholesterol

» Emulsify fats

Hepatic Portal System

14.2 Three Accessory Organs

• The Gallbladder– Excess bile stored– Secreted through common bile duct– Cholesterol can precipitate out of solution

• Forms crystals• Can become gall stones• Obstructive jaundice

14.3 Digestive Enzymes

• Digestive Enzymes

– Proteins with a particular shape that fits their

substrate.

– Have an optimum pH which maintains their shape

– Break down carbohydrates, proteins, nucleic acids,

and fats

14.3 Digestive Enzymes

• Salivary Amylase– Catalyzes the reaction: Starch+ H2O Maltose

• Occurs in the mouth • Maltose must be broken down to glucose for absorption

• Pepsin– Catalyzes the reaction: Protein + H2O Peptides

• Pepsinogen activated to pepsin by pH<2• Occurs in the stomach in presence of HCl

14.3 Digestive Enzymes

• Pancreatic Amylase– Catalyzes the reaction: Starch + H2O Maltose

• Occurs in duodenum– pH in duodenum is slightly basic from sodium bicarbonate– Optimal pH for pancreatic amylase

• Completes digestion of starches to dissaccharides

• Trypsin– Catalyzes the reaction: Protein + H2O Peptides

• Occurs in duodenum• Produced by pancreas as trypsinogen which is converted to

trypsin

14.3 Digestive Enzymes

• Lipase– Catalyzes the reaction:

Fats + H2O Glycerol + 3 fatty acids

– Emulsification by bile salts occurs first– Occurs in duodenum– Glycerol and fatty acids absorbed into villi– Rejoined and packaged as lipoproteins which are

absorbed into lacteals

14.3 Digestive Enzymes

• Peptidases– Catalyze Reaction: Peptides + H2O Amino Acids

• Occurs in small intestine• Absorbed into villi

• Maltase– Catalyzes Reaction:

Maltose + H2O Glucose + Glucose• Occurs in small intestine• Each disaccharide has its own enzyme• Lack of any one of these can cause illness

Major Digestive Enzymes

Digestion Experiment

14.4 Nutrition

• Nutrition– Science of foods and nutrients

• Nutrient- component of food that performs physiological function

– All body functions depend on proper nutrition

• Nutrients– Carbohydrates

• Primary energy source

– Fats• Energy storage

– Proteins• Growth and development• Regulate metabolism• Can be energy source

14.4 Nutrition

• Nutrients– Water

• Cells are 70-80% water

– Vitamins and minerals• Coenzymes and cofactors

• Food Pyramid– Guides food choices to fulfill needs– Emphasize foods in broad base areas– Minimize foods at tip– Guidelines change as nutritionists gain information

Food Guide Pyramids

14.4 Nutrition

• Guidelines– Balance energy input with energy output to maintain

weight– Eat a variety of foods– A healthy diet

• A moderate total fat intake low in saturated fats and cholesterol• Whole grains, legumes,vegetables for fiber and complex

carbohydrates• Low in refined carbohydrates• Low in salt and sodium• Adequate protein from poultry, fish, plants• Low or moderate alcohol consumption• Adequate vitamins and minerals

– Avoid questionable supplements-may be contraindicated

14.4 Nutrition

• Carbohydrates

– Glucose is the most readily available energy source• Stored by liver as glycogen

– Between meals liver can keep blood glucose constant by:

» The breakdown of glycogen» The conversion of amino acids and fat to

glucose• Body cells can use fatty acids for energy• Brain cells can only use glucose

14.4 Nutrition

• Carbohydrates

– Complex carbohydrates• Gradually broken down to glucose• Contain fiber

– Insoluble fiber-may protect against cancer– Soluble fiber-combines with bile acids and cholesterol

Complex Carbohydrates

14.4 Nutrition

• Carbohydrates

– Simple Sugars• High glycemic index - elevate blood sugar rapidly• This causes the pancreas to releases an overload of insulin• Sugar is then taken up rapidly, hunger returns quickly• Can lead to insulin resistance

Reducing High Glycemic Index Carbohydrates

14.4 Nutrition

• Proteins– Following the digestion of proteins, amino acids enter

the bloodstream and are transferred to tissues

– Amino acids are usually not used as an energy

source, rather they are used to make structural

proteins (muscle, hair, skin, nails)

– Others are used to synthesis proteins such as

hemoglobin, plasma proteins, enzymes, hormones

14.4 Nutrition

• Proteins

– Adequate protein formation requires 20 amino acids

• 8 must be supplied in the diet (essential amino

acids)

• The remaining 12 can be synthesized by the body

14.4 Nutrition

• Proteins – Complete proteins

• Contain all 20 amino acids• Eggs, meat, milk

– Incomplete proteins• Proteins of plant origin• Each lacks at least essential amino acids• Vegetarians must combine plant protein sources

– Protein complementary– Legumes with grains-provides all 20 amino acids

Complementary Proteins

14.4 Nutrition

• Proteins– Amino acids are not stored– Must take in daily supply– Too high intake of protein can be harmful

• Deamination of amino acids produces urea• Urea excretion requires water• Dehydration especially if individual is exercising• Can also cause calcium loss

– Some protein foods also are high in saturated fats• Red meat• Can lead to cardiovascular disease

14.4 Nutrition

• Lipids (Fats, oils, and cholesterol)

– Saturated Fats• Solids at room temperature

• Usually of animal origin

– Exceptions: palm oil, coconut oil

• Associated with cardiovascular disease

• Trans fatty acids are worst

– Hydrogenated unsaturated fatty acids

– Found largely in commercial products

– May reduce ability to clear cholesterol

– Associated with heart disease and diabetes

14.4 Nutrition

• Lipids– Unsaturated Fats

• Oils have percentage of mono- and polyunsaturated fats• Polyunsaturated oils contain essential fatty acids that can

only be obtained through the diet– Linoleic and linolenic acid

– Omega-3 fatty acids• Especially protective against heart disease• Cold water fish, flax seed oil, olive oil, canola oil

14.4 Nutrition

• Lipids– Fats That Cause Disease

• Plaques- form in arteries– Contain cholesterol and saturated fats

• Cholesterol– Carried in blood by low density lipoprotein (LDL) and high

density lipoprotein (HDL)

– LDL (”bad” cholesterol) - transports cholesterol from the liver to cells

– HDL- (“good” cholesterol) - transports cholesterol to the liver to make bile salts

Reducing Certain Lipids

14.4 Nutrition

• Vitamins– Organic compounds

• Many are coenzymes• Deficiencies produce specific symptoms

– 13 vitamins• Fat soluble- A,D,E,K• Water soluble- remaining 9

– Antioxidants-defend against free radicals• Vitamins C,E, and A• Cell metabolism generates free radicals

– O2- and OH-

– Cause cell damage

14.4 Nutrition

• Vitamins

– Vitamin D• Converted in skin to active form by UV light

• Further modification in kidneys and liver

– Becomes calcitrol

– Promotes calcium absorption from intestines

• Deficiency causes rickets

Illnesses Due to Vitamin Deficiency

Fat-Soluble Vitamins

Water-Soluble Vitamins

14.4 Nutrition

• Minerals

– Major Minerals• Body contains more than 5 grams

• Constituents of cells

• Structural components

– Trace Minerals• Body contains less than 5 grams

• Components of larger molecules

Minerals in the Body

Minerals

Reducing Dietary Sodium

14.4 Nutrition

• Eating Disorders– Obesity

• Body weight 20% above normal

• Hormonal, metabolic, and social factors are known causes

• Higher risk of heart disease

• Behavior modification and a proper diet is the usual treatment

Recognizing Bulimia

Recognizing Anorexia Nervosa