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Chapter 15 Lecture Outline See separate PowerPoint slides for all figures and tables preinserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 15.1 Anatomy of the digestive system 2 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 3 Structures of the digestive system 4 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 5 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 6 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 7 Human teeth 8 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 9 D. The pharynx 1. 2. Passageway for food and air 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) 10 E. Swallowing 1. 2. 3. Begins with the voluntary phase Reflex action – once food or drink is pushed back to the oropharynx Bolus – chewed and swallowed food or drink 11 Swallowing 12 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 13 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 14 Wall of the alimentary canal 15 G. The esophagus 1. 2. 3. 4. 5. Muscular tube from the pharynx to the stomach Peristalsis pushes food along the alimentary canal Function is to transport food to the stomach; no chemical digestion Esophageal sphincter marks the entrance to the stomach Heartburn occurs when some of the stomach contents escapes into the esophagus; GERD – chronic reflux disorder 16 Peristalsis 17 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 18 5. Regions of the stomach a. b. c. d. Cardiac stomach Fundic stomach Body of the stomach Pyloric stomach 19 Anatomy & histology of the stomach 20 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 21 g. Makeup of gastric juice 1) Chief cells a) Secrete pepsinogen b) Pepsinogen becomes the proteindigesting 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 22 Gastric juice, cont 3) 4) 5) Enteroendocrine cells produce gastrin that regulates muscular contractions and secretions of the stomach Mucous cells secrete protective mucus ECL cells release histamine to enhance the action of gastrin 23 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 24 Function of the mesentery 25 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 26 Regions of the small intestine 27 3. Wall of the small intestine a. b. c. d. Wall is modified to greatly increase surface area Circular folds – permanent transverse folds Villi – finger-like projections containing blood capillaries and a lacteal (lymphatic capillary) Microvilli – microscopic extensions of the columnar cells; called the brush border 28 Anatomy of the small intestine 29 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 30 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 31 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 32 e. Hormonal control 1) 2) 3) 4) 5) 6) Gastrin - causes gastric contraction and secretion by gastric glands Secretin – causes bicarbonate release from pancreas & liver production of bile Gastric inhibitory peptide (GIP) – inhibits gastric action & slows contractions Cholecystokinin (CCK) – causes enzyme release from pancreas & gall bladder release of bile Leptin – from adipocytes, causes full feeling Ghrelin – from stomach, triggers hunger 33 Hormonal control of secretion 34 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 35 The large intestine 36 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 37 6. Defecation reflex a. b. c. d. Rectal muscles contract and relax the internal anal sphincter Feces move into the anal canal Voluntary relaxation of the external anal sphincter and a pushing movement, propels the feces from the body There is much variation in the frequency of defecation 38 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 39 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 40 15.2 Accessory organs of digestion Teeth and salivary glands were covered with the oral cavity 41 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 chyme b. Digestive enzymes for all types of foods 1) Amylase digests starch 2) Three protein-digesting enzymes – released in inactive forms a) Trypsin – activated by enterokinase b) Chymotrypsin and Carboxypeptidase – activated by trypsin 3) Lipase digests fat 4) Nucleases break down nucleic acids 42 The pancreas 43 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 44 Liver structure, cont d. e. Bile ducts merge to form the common hepatic duct Central veins from each lobule enters a hepatic vein 45 Liver anatomy 46 2. Liver functions a. b. c. d. e. Detoxifies blood Removes and stores nutrients Stores iron and vitamins A, D, E, and K Makes plasma proteins 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) 47 Liver functions, cont f. g. h. Produces urea after breaking down amino acids Forms and secretes bile Helps regulate the blood cholesterol level 48 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 49 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 50 15.3 Chemical Digestion 51 A. Digestive enzymes 1. 2. 3. Digestive enzymes are hydrolytic enzymes Break down substances with the addition of water at specific bonds Have an optimum pH to function at 52 B. Carbohydrates 1. 2. 3. 4. 5. Salivary amylase breaks carbohydrates into maltose Action stops in the stomach (too acidic) Pancreatic amylase continues the hydrolysis to maltose 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 Monosaccharides are absorbed by intestinal cells into blood capillaries 53 Carbohydrate digestion & absorption 54 C. Proteins 1. 2. 3. 4. Pepsin in the stomach hydrolyzes proteins into short polypeptides Three pancreatic proteinases – trypsin, chymotrypsin, and carboxypeptidase break down polypeptides to peptides and some amino acids Peptidases (brush border enzymes) complete the digestion of peptides into amino acids in the small intestine Amino acids are absorbed by intestinal cells into blood capillaries 55 Protein digestion & absorption 56 D. Fats 1. 2. 3. First emulsified by bile in the duodenum Digested by pancreatic lipase to glycerol and fatty acids Enter intestinal cells where the fatty acids are packaged as lipoproteins and then enter the lacteals 57 Fat digestion & absorption 58 E. Nucleic acids 1. 2. 3. Pancreatic nucleases break down DNA and RNA into nucleotides Brush border nucleotidases break down the nucleotides to sugar, phosphate, and nitrogenous base These chemicals enter intestinal cells into the blood capillaries 59 Major digestive enzymes 60 15.4 Effects of aging 61 A. Effects of Aging 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Incidence of gastrointestinal disorders increases Periodontitis Esophageal hiatal hernia Heartburn & GERD Peristalsis slows Peptic ulcers may occur more frequently Diverticulosis and constipation – not enough fiber The liver shrinks Gallbladder difficulties occur – gallstones Cancer Hemorrhoids Fecal incontinence 62 15.5 Homeostasis 63 A. Homeostasis 1. 2. 3. 4. Alimentary canal is also part of the endocrine system Nutrients absorbed by the alimentary canal are used for energy, growth, and repair Vitamins needed for normal growth and development Minerals assist in many body processes 64 Human Systems Working Together 65 15.6 Nutrition 66 A. Nutrition 1. 2. 3. 4. Nutrition – interaction between food and the living organism Nutrient – substance the body uses to maintain health A balanced diet contains all the essential nutrients in correct proportions Nutrients enter the blood and are distributed to the tissues 67 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 68 Newest dietary guidelines Go to www.choosemyplate.gov to personalize 69 B. Vitamins 1. 2. 3. 4. Vital to life Play essential roles in cellular metabolism Fat-soluble - vitamins A, D, E, and K Water-soluble a. B-complex vitamins and vitamin C b. Most are coenzymes 70 Vitamins 71 C. Minerals 1. 2. Inorganic elements Macronutrients a. Sodium b. Magnesium c. Phosphorus d. Chlorine e. Potassium f. Calcium 3. Micronutrients – trace elements needed in very small amounts 72 Minerals 73 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 74 2. Bulimia nervosa a. b. c. d. e. Can coexist with either obesity or anorexia nervosa Binge eating, then purging Alters blood composition, leading to abnormal heart rhythm, kidney failure and even death Stomach acids can cause teeth to erode Esophagus and stomach may rupture 75 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 76 Anorexia Nervosa & Bulimia Nervosa 77