Transcript Chapter 21c
Chapter 21c The Digestive System The Cephalic Phase • Chemical and mechanical digestion begins in the mouth • Salivary secretion is under autonomic control • Softens and lubricates food • Chemical digestion: Salivary amylase and some lipase • Saliva also has a protective function • Chewing: mastication Swallowing Reflex 1 Tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex. Soft palate Hard palate Tongue Bolus Epiglottis Glottis Larynx Tonically contracted upper esophageal sphincter Figure 21-24, step 1 Swallowing Reflex 2 Upper esophageal sphincter relaxes while epiglottis closes to keep swallowed material out of the airways. Epiglottis Figure 21-24, step 2 Swallowing Reflex 3 Food moves downward into the esophagus, propelled by peristaltic waves and aided by gravity. Figure 21-24, step 3 The Gastric Phase • Storage • Stomach • Digestion • Stomach • Acid, enzymes, and signal molecules • Protection The Gastric Phase • Activity of secretory cells of the gastric mucosa Gastric mucosa Cell Types Substance Secreted Stimulus for Release Mucus Opening of gastric gland Mucous neck cell Bicarbonate Tonic secretion; with irritation of mucosa Secreted with mucus Gastric acid (HCl) Parietal cells Intrinsic factor EnterochromaffinHistamine like cell D cells G cells Physical barrier between lumen and epithelium Buffers gastric acid to prevent damage to epithelium Activates pepsin; kills bacteria Complexes with vitamin B12 to permit absorption Acetylcholine, gastrin Stimulates gastric acid secretion Digests proteins Gastric lipase Acetylcholine; acid, secretin Somatostatin Acid in the stomach Inhibits gastric acid secretion Gastrin Acetylcholine, peptides and amino acids Stimulates gastric acid secretion Pepsin(ogen) Chief cells Acetylcholine, gastrin, histamine Function of Secretion Digests fats Figure 21-25 The Gastric Phase • Integration of cephalic and gastric phase secretion in the stomach 1 1 Food Input via vagus nerve Gastric mucosa Lumen of stomach Amino acids or peptides G cell + D cell 2 Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. Gastrin 2 3 Acid stimulates short reflex secretion of pepsinogen. Somatostatin 4 Negative feedback pathway Histamine 4 Somatostatin release by H+ is the negative feedback signal that modulates acid and pepsin release. ECL cell Parietal cell H+ 3 Pepsin 1 Food or cephalic reflexes initiate gastric secretion. Enteric sensory neuron Pepsinogen Enteric sensory neuron Enteric plexus Chief cell Figure 21-26 The Gastric Phase 1 1 Food Input via vagus nerve Gastric mucosa Lumen of stomach Amino acids or peptides 1 Enteric sensory neuron Food or cephalic reflexes initiate gastric secretion. G cell Gastrin Enteric plexus Figure 21-26, step 1 The Gastric Phase 1 1 Food Input via vagus nerve Gastric mucosa Lumen of stomach Amino acids or peptides G cell Gastrin 2 Histamine H+ 1 Food or cephalic reflexes initiate gastric secretion. 2 Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. Enteric sensory neuron ECL cell Parietal cell Enteric plexus Figure 21-26, steps 1–2 The Gastric Phase 1 1 Food Input via vagus nerve Gastric mucosa Lumen of stomach 1 Food or cephalic reflexes initiate gastric secretion. 2 Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. 3 Acid stimulates short reflex secretion of pepsinogen. Enteric sensory neuron Amino acids or peptides G cell Gastrin 2 Histamine Parietal cell H+ 3 Pepsin ECL cell Pepsinogen Enteric sensory neuron Enteric plexus Chief cell Figure 21-26, steps 1–3 The Gastric Phase 1 1 Food Input via vagus nerve Gastric mucosa Lumen of stomach 1 Food or cephalic reflexes initiate gastric secretion. 2 Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. 3 Acid stimulates short reflex secretion of pepsinogen. 4 Somatostatin release by H+ is the negative feedback signal that modulates acid and pepsin release. Enteric sensory neuron Amino acids or peptides G cell Gastrin 2 + D cell Somatostatin 4 Negative feedback pathway Histamine Parietal cell H+ 3 Pepsin ECL cell Pepsinogen Enteric sensory neuron Enteric plexus Chief cell Figure 21-26, steps 1–4 The Gastric Phase • The mucus-bicarbonate barrier of the gastric mucosa Stomach lumen Gastric juice pH ~ 2 The mucus layer is a physical barrier. HCO3– Bicarbonate is a chemical HCO3– barrier that neutralizes acid. pH ~ 7 at cell surface Mucus layer Mucus droplets Gastric mucous cell Capillary Figure 21-27 Reflexes of Cephalic and Gastric Phases • Long and short reflexes of the cephalic and gastric phases of digestion Figure 12-23 The Intestinal Phase • Chyme in the small intestine inhibits gastric motility and secretion Food into stomach Acid secretion STOMACH Pepsin and lipase secretion Gastric motility Chyme into small intestine SMALL INTESTINE Hyperosmotic solution ? Endocrine cell PANCREAS Carbohydrates GIP GLP-1 Insulin secretion Enteric nervous system Fats, proteins Acid CCK Secretin Pancreatic enzyme secretion Pancreatic bicarbonate secretion Figure 21-28 The Intestinal Phase • Bicarbonate neutralizes gastric acid • Goblet cells secrete mucus for protection and lubrication • Bile • Fat digestion • Digestive enzymes • Enteropeptidase The Intestinal Phase • Activation of pancreatic zymogens Lumen of small intestine Pancreatic duct Pancreatic secretions (include inactive zymogens) Trypsinogen ZYMOGENS • Chymotrypsinogen • Procarboxypeptidase • Procolipase • Prophospholipase Enteropeptidase in brush border activates trypsin. Trypsin activates ACTIVATED ENZYMES • Chymotrypsin • Carboxypeptidase • Colipase • Phospholipase Intestinal mucosa Figure 21-29 Hepatic Portal System • Most fluid is absorbed in the small intestine Aorta Capillaries of liver Hepatic vein Inferior vena cava Liver Hepatic artery Capillaries of digestive tract: stomach, intestines, pancreas, and spleen Hepatic portal vein Digestive tract arteries Figure 21-30 The Intestinal Phase • Most digestion occurs in small intestine • Large intestine concentrates waste for excretion • Motility in large intestine • Mass movement triggers defecation • Defecation reflex • Digestion and absorption in large intestine • Diarrhea can cause dehydration The Intestinal Phase: Anatomy of the Large Intestine Hepatic portal vein Aorta Tenia coli Lymphoid nodule Intestinal glands Inferior vena cava Transverse colon Muscularis mucosae Submucosa Ascending colon Descending colon Ileocecal valve Ileum Longitudinal layer (tenia coli) Circular muscle Muscularis externa Haustra Cecum Sigmoid colon Appendix Rectum Rectum Internal anal sphincter External anal sphincter Anus Figure 21-31 The Intestinal Phase: Anatomy of the Large Intestine Figure 21-31 (1 of 3) The Intestinal Phase: Anatomy of the Large Intestine Figure 21-31 (2 of 3) The Intestinal Phase: Anatomy of the Large Intestine Figure 21-31 (3 of 3) Immune Function • M cells sample the contents of the gut • Immune cells secrete cytokines • Cytokines trigger inflammatory response • Increase in Cl–, fluid, and mucus secretion • Vomiting is a protective reflex Summary • Function and processes • Digestion, absorption, motility, secretion, and GALT • Anatomy • Motility • Tonic and phasic contractions • Slow wave potentials, interstitial cells of Cajal, migrating motor complex, peristaltic contractions, and segmental contractions Summary • Secretion • Parietal cells, CFTR chloride channel, mucous cells, goblet cells, saliva, and bile salts • Regulation • Short reflexes, ENS, long reflexes, intrinsic neurons, gastrin family, secretin family, and other hormones Summary • Digestion and absorption • Amylase, disaccharidases, endopeptidases, exopeptidases, lipase, colipase, micelles, chylomicrons, and intrinsic factor • The cephalic phase • The gastric phase • Mucous cells, chief cells, D cells, ECL cells, and G cells Summary • The intestinal phase • Brush border, mass movement, and defecation reflex • Immune functions • M cells and vomiting