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Structure and Function of the Digestive System Chapter 38 1 Gastrointestinal Tract Mouth Esophagus Stomach Small intestine Large intestine Rectum Anus 2 Mosby items and derived items © 2006 by Mosby, Inc. Gastrointestinal Tract 3 Mosby items and derived items © 2006 by Mosby, Inc. Gastrointestinal Tract Ingestion of food Propulsion of food and wastes from the mouth to the anus Secretion of mucus, water, and enzymes Mechanical digestion of food particles Chemical digestion of food particles Absorption of digested food Elimination of waste products by defecation 4 Mosby items and derived items © 2006 by Mosby, Inc. Gastrointestinal Tract Histology Mucosa Submucosa Muscularis Serosa or adventitia Enteric plexus Submucosal plexus Myenteric plexus Subserosal plexus 5 Mosby items and derived items © 2006 by Mosby, Inc. Gastrointestinal Tract 6 Mosby items and derived items © 2006 by Mosby, Inc. Mouth Reservoir for chewing and mixing of food with saliva Taste buds Salty, sour, bitter, and sweet Olfactory nerves Teeth 32 permanent teeth 7 Mosby items and derived items © 2006 by Mosby, Inc. Salivary Glands Three pairs Submandibular Sublingual Parotid Saliva Water with mucus, sodium, bicarbonate, chloride, potassium, and salivary α-amylase (carbohydrate digestion) Controlled by sympathetic and parasympathetic fibers 8 Mosby items and derived items © 2006 by Mosby, Inc. Swallowing Esophagus Peristalsis Primary and secondary Upper esophageal sphincter Lower esophageal sphincter Phases Oral and pharyngeal phases Esophageal phase 9 Mosby items and derived items © 2006 by Mosby, Inc. Stomach The stomach is a hollow, muscular organ that stores food, secretes digestive juices, mixes food with the juices, and propels partially digested food (chyme) Muscle layers Longitudinal Circular Oblique 10 Mosby items and derived items © 2006 by Mosby, Inc. Stomach Boundaries Cardiac orifice Pyloric sphincter Pylorus Functional areas Fundus Body Antrum 11 Mosby items and derived items © 2006 by Mosby, Inc. Stomach 12 Mosby items and derived items © 2006 by Mosby, Inc. Gastric Motility Swallowing Gastrin Cholecystokinin Motilin Secretin Gastric emptying 13 Mosby items and derived items © 2006 by Mosby, Inc. Gastric Secretion The stomach secretes large volumes of gastric juices Mucus Acid Enzymes Hormones Intrinsic factor Gastroferrin 14 Mosby items and derived items © 2006 by Mosby, Inc. Gastric Secretion Gastric pits Gastric glands Parietal cells Chief cells Hydrochloric acid and intrinsic factor Pepsinogen G cells Gastrin 15 Mosby items and derived items © 2006 by Mosby, Inc. Gastric Secretion Gastric glands Enterochromaffin-like cells Histamine D cells Somatostatin 16 Mosby items and derived items © 2006 by Mosby, Inc. Gastric Pits and Gastric Glands 17 Mosby items and derived items © 2006 by Mosby, Inc. Gastric Secretion Phases of gastric secretion Cephalic phase Gastric phase Intestinal phase 18 Mosby items and derived items © 2006 by Mosby, Inc. Small Intestine 5 to 6 meters long Three segments Duodenum Jejunum Ileum Ileocecal valve Peritoneum Peritoneal cavity 19 Mosby items and derived items © 2006 by Mosby, Inc. Small Intestine Muscle layers Mucosal folds (plica) Villi Microvilli Outer—longitudinal Inner—circular Brush border Lamina propria Lacteal 20 Mosby items and derived items © 2006 by Mosby, Inc. Small Intestine 21 Mosby items and derived items © 2006 by Mosby, Inc. Intestinal Digestion and Absorption Hydrochloric acid Pepsin Pancreatic enzymes Intestinal enzymes Bile salts 22 Mosby items and derived items © 2006 by Mosby, Inc. Intestinal Digestion and Absorption Carbohydrates Proteins Fats Water Electrolytes 23 Mosby items and derived items © 2006 by Mosby, Inc. Intestinal Digestion and Absorption 24 Mosby items and derived items © 2006 by Mosby, Inc. Intestinal Digestion and Absorption 25 Mosby items and derived items © 2006 by Mosby, Inc. Intestinal Digestion and Absorption 26 Mosby items and derived items © 2006 by Mosby, Inc. Intestinal Motility The movements of the small intestine facilitate both digestion and absorption Segmentation Peristalsis Ileogastric reflex Intestinointestinal reflex Gastroileal reflex 27 Mosby items and derived items © 2006 by Mosby, Inc. Large Intestine Cecum Appendix Colon Ascending Transverse Descending Sigmoid Rectum Anus 28 Mosby items and derived items © 2006 by Mosby, Inc. Large Intestine 29 Mosby items and derived items © 2006 by Mosby, Inc. Large Intestine Ileocecal valve O’Beirne sphincter Internal anal sphincter External anal sphincter Taenia coli Haustra 30 Mosby items and derived items © 2006 by Mosby, Inc. Gastrointestinal Absorption 31 Mosby items and derived items © 2006 by Mosby, Inc. Intestinal Bacteria The environment of the stomach is relatively sterile because of secreted stomach acid Bile acid secretion, motility, and antibody production keeps bacterial numbers in the duodenum to a minimum There is a low concentration of aerobes in the jejunum Anaerobic bacteria are distal to the ileocecal valve Anaerobes are 95% of the fecal flora in the colon 32 Mosby items and derived items © 2006 by Mosby, Inc. Accessory Organs of Digestion 33 Mosby items and derived items © 2006 by Mosby, Inc. Accessory Organs of Digestion Liver Lobes Separated and attached to the anterior abdominal wall by the falciform ligament Right lobe Caudate and quadrate lobes Left lobe Glisson capsule 34 Mosby items and derived items © 2006 by Mosby, Inc. Liver 35 Mosby items and derived items © 2006 by Mosby, Inc. Hepatic Portal Circulation 36 Mosby items and derived items © 2006 by Mosby, Inc. Liver Liver lobules Hepatocytes Lipocytes Sinusoids Bile canaliculi Common bile duct Major duodenal papilla (sphincter of Oddi) 37 Mosby items and derived items © 2006 by Mosby, Inc. Liver Lobules 38 Mosby items and derived items © 2006 by Mosby, Inc. Liver Kupffer cells Stellate cells Pit cells Disse space 39 Mosby items and derived items © 2006 by Mosby, Inc. Secretion of Bile Bile is an alkaline, bitter-tasting, yellowish green fluid that contains bile salts, cholesterol, bilirubin, electrolytes, and water Bile is formed by hepatocytes and secreted into the bile canaliculi Enterohepatic circulation Recycling of bile salts 40 Mosby items and derived items © 2006 by Mosby, Inc. Enterohepatic Circulation 41 Mosby items and derived items © 2006 by Mosby, Inc. Metabolism of Bilirubin Bilirubin is a by-product of the destruction of aged red blood cells Bilirubin gives bile a greenish black color and produces the yellow tinge of jaundice Unconjugated bilirubin Conjugated bilirubin Urobilinogen 42 Mosby items and derived items © 2006 by Mosby, Inc. Metabolism of Bilirubin 43 Mosby items and derived items © 2006 by Mosby, Inc. Vascular and Hematologic Liver Functions Blood storage Bacterial and foreign particle removal Synthesizes clotting factors Produces bile to absorb fat-soluble vitamins Metabolizes fats 44 Mosby items and derived items © 2006 by Mosby, Inc. Vascular and Hematologic Liver Functions Metabolizes proteins Metabolizes carbohydrates Metabolic detoxification Storage of minerals and vitamins 45 Mosby items and derived items © 2006 by Mosby, Inc. Gallbladder The gallbladder is a saclike organ that lies on the inferior surface of the liver The function of the gallbladder is to store and concentrate bile between meals The gallbladder holds about 90 mL of bile 46 Mosby items and derived items © 2006 by Mosby, Inc. Exocrine Pancreas The exocrine pancreas is composed of acini and networks of ducts that secrete enzymes and alkaline fluids to assist in digestion Pancreatic duct Ampulla of Vater 47 Mosby items and derived items © 2006 by Mosby, Inc. Exocrine Pancreas 48 Mosby items and derived items © 2006 by Mosby, Inc. Exocrine Pancreas Secretions Potassium, sodium, bicarbonate, magnesium, calcium, and chloride Enzymes Trypsinogen, chymotrypsinogen, and procarboxypeptidase Trypsin inhibitor Pancreatic α-amylase Pancreatic lipase 49 Mosby items and derived items © 2006 by Mosby, Inc. Aging and the Digestive Function Tooth enamel and dentin wear down Teeth are lost Periodontal disease Gum recession Osteoporotic bone changes 50 Mosby items and derived items © 2006 by Mosby, Inc. Aging and the Digestive Function Number of taste buds decline Sense of smell diminishes Salivary secretion decreases Decreased esophageal and gastric motility 51 Mosby items and derived items © 2006 by Mosby, Inc.
