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Chapter 15
Lecture and
Animation Outline
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15.1 Anatomy of the digestive system
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A. Introduction
1. Also called the alimentary canal or gastrointestinal (GI) tract
2. Digestion includes both physical and chemical processes that reduce food into soluble molecules that can be absorbed into the blood stream
3. Functions of the digestive system:
a. Ingest food
b. Break food down into small molecules
c. Absorb nutrient molecules
d. Eliminate non-digestible wastes
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Structures of the digestive system
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Digestive System Overview
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B. The mouth (oral cavity)
1. Tongue
a. Composed of skeletal muscle
b. Papillae
1) Help it handle food
2) Contain taste buds
c. Lingual frenulum attaches it to the floor of the mouth
2. Roof separates the oral cavity from the nasal cavities
a. Hard palate
b. Soft palate
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C. Teeth and salivary glands
1. Teeth
a. 20 deciduous (baby) teeth
b. 32 adult teeth embedded in the maxilla and mandible
1) 4 incisors per jaw
2) 2 cuspids (canines) per jaw
3) 4 bicuspids per jaw
4) 6 molars per jaw
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Teeth, cont.
c. Tooth structure
1) Crown – layers of enamel, dentin, and pulp
2) Root – layers of cementum, dentin, and pulp
d. Diseases
1) Caries occur when bacteria break down sugars and produce acids that erode the enamel
2) Gum diseases are more likely as we age – gingivitis and periodontitis
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2. Salivary glands
a. Salivary glands
1) Parotid
2) Sublingual
3) Submandibular
b. Saliva – solution of mucus and water
1) Salivary amylase – begins the process of digesting carbohydrates
2) Moistens food and prepares it for swallowing
3) Antibacterial lysozyme and secretory antibodies
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D. The pharynx
1. Passageway for food and air
2. Three parts
a. Nasopharynx - air
b. Oropharynx – food and air
c. Laryngopharynx - food
3. Tonsils
a. Palatine tonsils
b. Lingual tonsils
c. Pharyngeal tonsil (adenoids)
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E. Swallowing
1. Begins with the voluntary phase
2. Reflex action – once food or drink is pushed back to the oropharynx
3. Bolus – chewed and swallowed food or drink
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F. The Wall of the Digestive Tract
1. Mucosa (mucous membrane layer)
a. Layer of epithelium that lines the lumen
b. Glandular epithelial cells secrete digestive enzymes
c. Goblet cells secrete mucus
2. Submucosa (submucosal layer)
a. Loose connective tissue
b. Contains blood vessels, lymphatic vessels, and nerves
c. Peyer’s patches are scattered throughout the submucosa of the small intestine
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Wall layers, cont
3. Muscularis (smooth muscle layer)
a. Inner, circular layer
b. Outer, longitudinal layer
c. The stomach has an extra oblique layer
4. Serosa (serous membrane layer)
a. Thin, outermost layer of squamous epithelium
b. Secretes serous fluid
c. Adventitia – outer connective tissue layer of the esophagus
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Wall of the alimentary canal
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G. The esophagus
1. Muscular tube from the pharynx to the stomach
2. Peristalsis pushes food along the alimentary canal
3. Function is to transport food to the stomach; no chemical digestion
4. Esophageal sphincter marks the entrance to the stomach
5. Heartburn occurs when some of the stomach contents escapes into the esophagus; GERD – chronic reflux disorder
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H. The stomach
1. Thick-walled, J-shaped organ on the left side of the abdominal cavity
2. Continuous with the esophagus and duodenum of the small intestine
3. Rugae – deep folds in its wall
4. Functions
a. Stores and liquefies food
b. Starts the digestion of proteins
c. Moves food into the small intestine
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5. Regions of the stomach
a. Cardiac stomach
b. Fundic stomach
c. Body of the stomach
d. Pyloric stomach
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Anatomy & histology of the stomach
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6. Digestive functions of the stomach
a. Acts on food both chemically and physically
b. Muscular wall churns and mixes food with gastric juice
c. Gastric pits lead to gastric glands that produce gastric juice
d. Alcohol and water are absorbed through the stomach wall
e. Churned food and gastric juice mixture is called chyme which leaves the stomach in 2 to 6 hours
f. Ulcer – open sore, mainly caused by the bacterium, Helicobacter pylori
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g. Makeup of gastric juice
1) Chief cells
a) Secrete pepsinogen
b) Pepsinogen becomes the protein-digesting enzyme pepsin when activated by HCl
2) Parietal cells
a) Produce hydrochloric acid – kills bacteria and activates pepsin
b) Produces intrinsic factor – binds to vitamin B12 and prevents it from being destroyed in the acidic environment
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Gastric juice, cont
3) Enteroendocrine cells produce gastrin that regulates muscular contractions and secretions of the stomach
4) Mucous cells secrete protective mucus
5) ECL cells release histamine to enhance the action of gastrin
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Stomach
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Hydrochloric Acid Production
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I. Peritoneum
1. Serous membrane of the abdominal cavity
2. Parietal peritoneum lines the abdominal wall
3. Visceral peritoneum covers the organs
a. Lesser omentum – mesentery that runs between the stomach and liver
b. Greater omentum – mesentery that hangs down in front of the intestines
1) Cushions and insulates the abdominal cavity
2) Contains macrophages
3) Can wall off portions of the alimentary wall that may be infected
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Function of the mesentery
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J. The small intestine
1. Extends from the pyloric valve of the stomach to the ileocecal valve where it joins the large intestine (about 18 ft in a cadaver)
2. Regions of the Small Intestine
a. Duodenum – many folds and villi
1) Glands secrete mucus
2) Receives pancreatic secretions and bile
b. Jejunum
c. Ileum contains Peyer’s patches with few folds and villi
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Regions of the small intestine
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3. Wall of the small intestine
a. Wall is modified to greatly increase surface area
b. Circular folds – permanent transverse folds
c. Villi – finger-like projections containing blood capillaries and a lacteal (lymphatic capillary)
d. Microvilli – microscopic extensions of the columnar cells; called the brush border
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Anatomy of the small intestine
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4. Functions of the small intestine
a. Digestion of fats, proteins, and carbohydrates into soluble molecules
1) Bile and pancreatic enzymes enter the duodenum for chemical digestion
2) Intestinal enzymes complete chemical digestion
b. Absorption of nutrients
1) Sugars and amino acids enter the blood
2) Glycerol and fatty acids enter the lacteal
c. Movement of nondigested remains to the large intestine
1) Segmentation
2) Peristalsis
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5. Regulation of contraction and secretion
a. The central nervous system allows a response to hunger signals
b. Enteric nervous system - a network of nerves within the walls of the GI tract that controls its own movements and secretions
c. Autonomic nervous system
1) Parasympathetic division is the major controller of digestive activities
2) Sympathetic division slows digestive activities
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d. Nervous control
1) Cephalic phase - Sight or smell of food causes parasympathetic stimulation of gastric secretion
2) Gastric phase – stretch of the stomach causes gastric contraction and secretion by gastric glands including gastrin
3) Intestinal phase – stretch of the duodenum causes contraction and secretion in the small intestine and feeds back to the stomach
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Three Phases of Gastric Secretion
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e. Hormonal control
1) Gastrin - causes gastric contraction and secretion by gastric glands
2) Secretin – causes bicarbonate release from pancreas & liver production of bile
3) Gastric inhibitory peptide (GIP) – inhibits gastric action & slows contractions
4) Cholecystokinin (CCK) – causes enzyme release from pancreas & gall bladder release of bile
5) Leptin – from adipocytes, causes full feeling
6) Ghrelin – from stomach, triggers hunger
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Hormonal control of secretion
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K. The large intestine
1. Has a larger diameter but is shorter than the small intestine
2. Functions
a. Absorbs water, salts, and some vitamins
b. Stores indigestible material until it is eliminated
3. Regions
a. Cecum - blind sac below ileocecal valve; vermiform appendix is attached
b. Colon - ascending colon, transverse colon, descending colon, sigmoid colon
1) Haustra
2) Taenia coli
c. Rectum
d. Anal canal
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The large intestine
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Large intestine, cont
4. Feces
a. 75% water
b. 25% solids
1) Bacteria
2) Fiber and other indigestible remains
c. Color comes from a breakdown product of bilirubin
5. Colon bacteria feed on cellulose and produce fatty acids, B-complex vitamins, vitamin K, and gases that contribute to flatus
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6. Defecation reflex
a. Rectal muscles contract and relax the internal anal sphincter
b. Feces move into the anal canal
c. Voluntary relaxation of the external anal sphincter and a pushing movement, propels the feces from the body
d. There is much variation in the frequency of defecation
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Reflexes of the Colon
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7. Irregular bowel movements
a. Constipation
1) Slow movement with more absorption of water
2) Feces are dry and hard
3) Chronic constipation is associated with hemorrhoids
b. Diarrhea
1) Fast movement with not enough water reabsorbed
2) Caused by infection of the lower intestinal tract or irregular nervous stimulation
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8. Other disorders of the large intestine
a. Polyps
1) Small growths arising from the epithelial lining of the colon
2) Can be benign or cancerous (colon cancer)
b. Diverticulosis
1) Presence of saclike pouches
2) Diverticulitis – inflammation occurs
a) Cramps or steady pain
b) Fever
c) Loss of appetite, nausea, and vomiting
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15.2 Accessory organs of digestion
Teeth and salivary glands were covered with the oral cavity
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A. Pancreas
1. Endocrine function – pancreatic islets secrete insulin, glucagon, and somatostatin
2. Exocrine function acinar cells produce pancreatic juice
a. Sodium bicarbonate to neutralize acidic chymeb. Digestive enzymes for all types of foods
1) Amylase digests starch2) Three protein-digesting enzymes – released
in inactive formsa) Trypsin – activated by enterokinaseb) Chymotrypsin and Carboxypeptidase –
activated by trypsin3) Lipase digests fat4) Nucleases break down nucleic acids
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B. The liver
1. Liver Structure
a. Two main lobes
b. Each lobe is divided into many hepatic lobules
1) Hepatic cells
2) Hepatic sinusoids
3) Kupffer cells – phagocytic macrophages
c. Portal triads are located between the lobules
1) Bile duct
2) A branch of the hepatic artery
3) A branch of the hepatic portal vein
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Liver structure, cont
d. Bile ducts merge to form the common hepatic duct
e. Central veins from each lobule enters a hepatic vein
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2. Liver functions
a. Detoxifies blood
b. Removes and stores nutrients
c. Stores iron and vitamins A, D, E, and K
d. Makes plasma proteins
e. Maintains blood glucose concentrations
1) Insulin stores glucose as glycogen (glycogenesis)
2) Glucagon breaks down glycogen to glucose (glycogenolysis)
3) New glucose made from other molecules (gluconeogenesis)
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Liver functions, cont
f. Produces urea after breaking down amino acids
g. Forms and secretes bile
h. Helps regulate the blood cholesterol level
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Liver
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3. Liver disorders
a. Jaundice – yellow tint to the whites of the eyes and skin due to bilirubin deposits
1) Hemolytic jaundice
2) Obstructive jaundice
3) Hepatitis
b. Cirrhosis – liver becomes fatty and then liver tissue is replaced by fibrous scar tissue
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C. The gallbladder
1. Sac on the inferior surface of the liver that stores and concentrates excess bile
2. When needed, bile leaves the gallbladder via the cystic duct
3. The cystic duct joins the common hepatic duct to form the common bile duct that enters the duodenum with the pancreatic duct
4. Function of bile salts
a. Emulsification of fats
b. Enhance absorption of fatty acids, cholesterol, and fat soluble vitamins
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15.3 Chemical Digestion
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A. Digestive enzymes
1. Digestive enzymes are hydrolytic enzymes
2. Break down substances with the addition of water at specific bonds
3. Have an optimum pH to function at
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B. Carbohydrates
1. Salivary amylase breaks carbohydrates into maltose
2. Action stops in the stomach (too acidic)
3. Pancreatic amylase continues the hydrolysis to maltose
4. Brush border enzymes of the small intestine break down disaccharides to monosaccharides (mainly glucose)
a. Sucrose broken down by sucrase
b. Lactose broken down by lactase
c. Maltose broken down by maltase
5. Monosaccharides are absorbed by intestinal cells into blood capillaries
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Hydrolysis of Sucrose
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Carbohydrate digestion & absorption
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C. Proteins
1. Pepsin in the stomach hydrolyzes proteins into short polypeptides
2. Three pancreatic proteinases – trypsin, chymotrypsin, and carboxypeptidase break down polypeptides to peptides and some amino acids
3. Peptidases (brush border enzymes) complete the digestion of peptides into amino acids in the small intestine
4. Amino acids are absorbed by intestinal cells into blood capillaries
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Protein digestion & absorption
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D. Fats
1. First emulsified by bile in the duodenum
2. Digested by pancreatic lipase to glycerol and fatty acids
3. Enter intestinal cells where the fatty acids are packaged as lipoproteins and then enter the lacteals
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Fat digestion & absorption
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E. Nucleic acids
1. Pancreatic nucleases break down DNA and RNA into nucleotides
2. Brush border nucleotidases break down the nucleotides to sugar, phosphate, and nitrogenous base
3. These chemicals enter intestinal cells into the blood capillaries
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Major digestive enzymes
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15.4 Effects of aging
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A. Effects of Aging
1. Incidence of gastrointestinal disorders increases
2. Periodontitis
3. Esophageal hiatal hernia
4. Heartburn & GERD
5. Peristalsis slows
6. Peptic ulcers may occur more frequently
7. Diverticulosis and constipation – not enough fiber
8. The liver shrinks
9. Gallbladder difficulties occur – gallstones
10. Cancer
11. Hemorrhoids
12. Fecal incontinence
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15.5 Homeostasis
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A. Homeostasis
1. Alimentary canal is also part of the endocrine system
2. Nutrients absorbed by the alimentary canal are used for energy, growth, and repair
3. Vitamins needed for normal growth and development
4. Minerals assist in many body processes
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Human Systems Working Together
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15.6 Nutrition
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A. Nutrition
1. Nutrition – interaction between food and the living organism
2. Nutrient – substance the body uses to maintain health
3. A balanced diet contains all the essential nutrients in correct proportions
4. Nutrients enter the blood and are distributed to the tissues
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Nutrition, cont
5. Essential molecules must be present in food because the body is unable to produce them
a. Two essential fatty acids
b. Nine essential amino acids
6. Glucose is the body’s immediate energy source
7. Fats are a long-term energy source
8. Amino acids used by the cells to construct proteins and can be used for energy is needed
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Newest dietary guidelines
Go to www.choosemyplate.gov to personalize
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B. Vitamins
1. Vital to life
2. Play essential roles in cellular metabolism
3. Fat-soluble - vitamins A, D, E, and K
4. Water-soluble
a. B-complex vitamins and vitamin C
b. Most are coenzymes
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C. Minerals
1. Inorganic elements
2. Macronutrients
a. Sodium
b. Magnesium
c. Phosphorus
d. Chlorine
e. Potassium
f. Calcium
3. Micronutrients – trace elements needed in very small amounts
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D. Eating disorders
1. Obesity
a. Body weight 20% or more above the ideal weight for a person’s height
b. 36% of women and 32% of men in the U.S. are overweight
c. Caused by a combination of factors –hormonal, metabolic, and social
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2. Bulimia nervosa
a. Can coexist with either obesity or anorexia nervosa
b. Binge eating, then purging
c. Alters blood composition, leading to abnormal heart rhythm, kidney failure and even death
d. Stomach acids can cause teeth to erode
e. Esophagus and stomach may rupture
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3. Anorexia nervosa
a. Morbid fear of gaining weight
b. Individuals have a distorted self-image
c. Individuals have all the symptoms of starvation
1) Low blood pressure
2) Irregular heartbeat
3) Constipation
4) Constant chilliness
5) Bone density decreases
6) Menstruation stops in females
7) Internal organs do not function well
8) Skin dries up
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Anorexia Nervosa & Bulimia Nervosa
