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Chapter 38 Structure and Function of the Digestive System Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Gastrointestinal Tract Mouth Esophagus Stomach Small intestine Large intestine Rectum Anus Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 2 Gastrointestinal Tract Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 3 Gastrointestinal Tract Functions: Overview Breaks down ingested food Prepares food for uptake by the body’s cells Provides body water Eliminates wastes Controlled by hormones and the autonomic nervous system (except for chewing, swallowing, and defecation) Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 4 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 by defecation Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 5 Gastrointestinal Tract Histology Mucosa Submucosa Muscularis Serosa or adventitia Enteric plexus Submucosal plexus Myenteric plexus Subserosal plexus Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 6 Gastrointestinal Tract Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 7 Mouth Reservoir for chewing and mixing of food with saliva Taste buds Salty, sour, bitter, and sweet Olfactory nerves Teeth 32 permanent teeth Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 8 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 Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 9 Swallowing Complex event mediated by the swallowing center, located in the reticular formation of the brainstem; also involves other brain regions, including the insula/claustrum and cerebellum The swallowing center and respiratory center provide the coordinating innervation Superior constrictor muscle of the pharynx contracts, prevents movement of food into the nasopharynx Respiration inhibited and epiglottis slides downward to prevent bolus from entering larynx and trachea Movements of tongue and pharyngeal constrictors propel the food into the esophagus in a series of coordinated events taking 1 or 2 seconds Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 10 Swallowing Esophagus Peristalsis Primary and secondary Upper esophageal sphincter Lower esophageal sphincter Phases Oral and pharyngeal phases Esophageal phase Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 11 Stomach 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 Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 12 Stomach Boundaries Cardiac orifice Pyloric sphincter Pylorus Functional areas Fundus Body Antrum Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 13 Stomach Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 14 Gastric Motility Swallowing Gastrin Cholecystokinin Motilin Secretin Gastric emptying Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 15 Gastric Secretion The stomach secretes large volumes of gastric juices Mucus Acid Enzymes Hormones Intrinsic factor Gastroferrin Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 16 Gastric Secretion Gastric pits Gastric glands Parietal cells • Hydrochloric acid and intrinsic factor Chief cells • Pepsinogen G cells • Gastrin Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 17 Gastric Secretion Gastric glands Enterochromaffin-like cells • Histamine D cells • Somatostatin Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 18 Gastric Pits and Gastric Glands Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 19 Gastric Secretion Phases of gastric secretion Cephalic phase Gastric phase Intestinal phase Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 20 Small Intestine 5 to 6 meters long Three segments Duodenum Jejunum Ileum • Ileocecal valve Peritoneum Peritoneal cavity Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 21 Small Intestine Muscle layers Mucosal folds (plica) Villi Microvilli Outer—longitudinal Inner—circular Brush border Lamina propria Lacteal Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 22 Small Intestine Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 23 Intestinal Digestion and Absorption Hydrochloric acid Pepsin Pancreatic enzymes Intestinal enzymes Bile salts Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 24 Intestinal Digestion and Absorption Carbohydrates Proteins Fats Water Electrolytes Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 25 Intestinal Digestion and Absorption Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 26 Intestinal Digestion and Absorption Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 27 Intestinal Digestion and Absorption Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 28 Intestinal Motility Movements of the small intestine facilitate digestion and absorption Segmentation Peristalsis Ileogastric reflex Intestinointestinal reflex Gastroileal reflex Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 29 Large Intestine Cecum Appendix Colon Ascending Transverse Descending Sigmoid Rectum Anus Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 30 Large Intestine Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 31 Large Intestine Ileocecal valve O’Beirne sphincter Internal anal sphincter External anal sphincter Taenia coli Haustra Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 32 Gastrointestinal Absorption Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 33 Intestinal Bacteria Stomach environment is relatively sterile because of secreted stomach acid Bile acid secretion, motility, and antibody production keep bacterial numbers in the duodenum to a minimum A low concentration of aerobes in the jejunum Anaerobic bacteria distal to the ileocecal valve Anaerobes are 95% of the fecal flora in the colon Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 34 Accessory Organs of Digestion Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 35 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 Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 36 Liver Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 37 Hepatic Portal Circulation Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 38 Liver Liver lobules Hepatocytes Lipocytes Sinusoids Bile canaliculi Common bile duct Major duodenal papilla (sphincter of Oddi) Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 39 Liver Lobules Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 40 Liver Kupffer cells Stellate cells Pit cells Disse space Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 41 Secretion of Bile Alkaline, bitter-tasting, yellowish green fluid that contains bile salts, cholesterol, bilirubin, electrolytes, and water Formed by hepatocytes and secreted into the bile canaliculi Enterohepatic circulation Recycling of bile salts Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 42 Enterohepatic Circulation Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 43 Metabolism of Bilirubin A byproduct of the destruction of aged red blood cells Gives bile a greenish black color and produces the yellow tinge of jaundice Unconjugated bilirubin Conjugated bilirubin Urobilinogen Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 44 Metabolism of Bilirubin Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 45 Vascular and Hematologic Liver Functions Blood storage Bacterial and foreign particle removal Synthesizes clotting factors Produces bile to absorb fat-soluble vitamins Metabolizes fats Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 46 Vascular and Hematologic Liver Functions Metabolizes proteins Metabolizes carbohydrates Metabolic detoxification Storage of minerals and vitamins Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 47 Gallbladder A sac-like organ that lies on the inferior surface of the liver Function is to store and concentrate bile between meals Gallbladder holds about 90 ml of bile Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 48 Exocrine Pancreas Composed of acini and networks of ducts that secrete enzymes and alkaline fluids to assist in digestion Pancreatic duct Ampulla of Vater Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 49 Exocrine Pancreas Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 50 Exocrine Pancreas Secretions Potassium, sodium, bicarbonate, magnesium, calcium, and chloride Enzymes Trypsinogen, chymotrypsinogen, and procarboxypeptidase Trypsin inhibitor Pancreatic α-amylase Pancreatic lipase Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 51 Aging and the Digestive Function Tooth enamel and dentin wear down Teeth are lost Periodontal disease Gum recession Osteoporotic bone changes Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 52 Aging and the Digestive Function Number of taste buds decline Sense of smell diminishes Salivary secretion decreases Decreased esophageal and gastric motility Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. 53
