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Chapter 21c The Digestive System. The Cephalic Phase Chemical and mechanical digestion begins in the mouth Salivary secretion is under autonomic control.

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Presentation on theme: "Chapter 21c The Digestive System. The Cephalic Phase Chemical and mechanical digestion begins in the mouth Salivary secretion is under autonomic control."— Presentation transcript:

1 Chapter 21c The Digestive System

2 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

3 Swallowing Reflex Figure 21-24, step 1 Tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex. Hard palate Tongue Bolus Epiglottis Tonically contracted upper esophageal sphincter Larynx Soft palate Glottis 1

4 Swallowing Reflex Figure 21-24, step 2 Upper esophageal sphincter relaxes while epiglottis closes to keep swallowed material out of the airways. Epiglottis 2

5 Swallowing Reflex Figure 21-24, step 3 Food moves downward into the esophagus, propelled by peristaltic waves and aided by gravity. 3

6 The Gastric Phase Storage Stomach Digestion Stomach Acid, enzymes, and signal molecules Protection

7 The Gastric Phase Activity of secretory cells of the gastric mucosa Figure Gastric mucosa Opening of gastric gland Cell TypesSubstance SecretedStimulus for ReleaseFunction of Secretion Mucous neck cell Mucus Bicarbonate Tonic secretion; with irritation of mucosa Secreted with mucus Physical barrier between lumen and epithelium Buffers gastric acid to prevent damage to epithelium Parietal cells Gastric acid (HCl) Intrinsic factor Acetylcholine, gastrin, histamine Activates pepsin; kills bacteria Complexes with vitamin B 12 to permit absorption Enterochromaffin- like cell Histamine Acetylcholine, gastrin Stimulates gastric acid secretion Chief cells Pepsin(ogen) Gastric lipase Acetylcholine; acid, secretin Digests proteins Digests fats D cells SomatostatinAcid in the stomach Inhibits gastric acid secretion G cells Gastrin Acetylcholine, peptides and amino acids Stimulates gastric acid secretion

8 The Gastric Phase Integration of cephalic and gastric phase secretion in the stomach Figure Lumen of stomach Gastric mucosa Enteric plexus Chief cell Gastrin Somatostatin Amino acids or peptides Input via vagus nerve Enteric sensory neuron ECL cell G cell D cell H+H+ Food Histamine PepsinPepsinogen Parietal cell Negative feedback pathway Food or cephalic reflexes initiate gastric secretion. Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. Acid stimulates short reflex secretion of pepsinogen. Somatostatin release by H + is the negative feedback signal that modulates acid and pepsin release

9 The Gastric Phase Figure 21-26, step 1 Lumen of stomach Gastric mucosa Enteric plexus Gastrin Amino acids or peptides Input via vagus nerve Enteric sensory neuron G cell Food Food or cephalic reflexes initiate gastric secretion

10 The Gastric Phase Figure 21-26, steps 1–2 Lumen of stomach Gastric mucosa Enteric plexus Gastrin Amino acids or peptides Input via vagus nerve Enteric sensory neuron ECL cell G cell H+H+ Food Histamine Parietal cell Food or cephalic reflexes initiate gastric secretion. Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine

11 The Gastric Phase Figure 21-26, steps 1–3 Lumen of stomach Gastric mucosa Enteric plexus Chief cell Gastrin Amino acids or peptides Input via vagus nerve Enteric sensory neuron ECL cell G cell H+H+ Food Histamine PepsinPepsinogen Parietal cell Food or cephalic reflexes initiate gastric secretion. Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. Acid stimulates short reflex secretion of pepsinogen

12 The Gastric Phase Figure 21-26, steps 1–4 Lumen of stomach Gastric mucosa Enteric plexus Chief cell Gastrin Somatostatin Amino acids or peptides Input via vagus nerve Enteric sensory neuron ECL cell G cell D cell H+H+ Food Histamine PepsinPepsinogen Parietal cell Negative feedback pathway Food or cephalic reflexes initiate gastric secretion. Gastrin stimulates acid secretion by direct action on parietal cells or indirectly through histamine. Acid stimulates short reflex secretion of pepsinogen. Somatostatin release by H + is the negative feedback signal that modulates acid and pepsin release

13 The Gastric Phase The mucus-bicarbonate barrier of the gastric mucosa Figure Capillary Stomach lumen Gastric juice pH ~ 2 Mucus layer Mucus droplets Gastric mucous cell pH ~ 7 at cell surface HCO 3 – The mucus layer is a physical barrier. Bicarbonate is a chemical barrier that neutralizes acid.

14 Reflexes of Cephalic and Gastric Phases Long and short reflexes of the cephalic and gastric phases of digestion Figure 12-23

15 The Intestinal Phase Chyme in the small intestine inhibits gastric motility and secretion Figure Acid secretion Gastric motility Pepsin and lipase secretion Enteric nervous system Acid Hyper- osmotic solution Carbohydrates Fats, proteins ? Endocrine cell GIPGLP-1 CCK Secretin Pancreatic bicarbonate secretion Pancreatic enzyme secretion Insulin secretion Food into stomach Chyme into small intestine STOMACH SMALL INTESTINE PANCREAS

16 The Intestinal Phase Bicarbonate neutralizes gastric acid Goblet cells secrete mucus for protection and lubrication Bile Fat digestion Digestive enzymes Enteropeptidase

17 The Intestinal Phase Activation of pancreatic zymogens Figure Lumen of small intestine Intestinal mucosa Pancreatic duct Chymotrypsinogen Procarboxypeptidase Procolipase Prophospholipase Chymotrypsin Carboxypeptidase Colipase Phospholipase Pancreatic secretions (include inactive zymogens) Trypsinogen Trypsin Enteropeptidase in brush border activates trypsin. ZYMOGENS ACTIVATED ENZYMES activates

18 Hepatic Portal System Most fluid is absorbed in the small intestine Figure Aorta Hepatic vein Inferior vena cava Digestive tract arteries Hepatic portal vein Hepatic artery Capillaries of liver Capillaries of digestive tract: stomach, intestines, pancreas, and spleen Liver

19 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

20 The Intestinal Phase: Anatomy of the Large Intestine Figure Rectum Internal anal sphincter Anus External anal sphincter Cecum Appendix Ileum Ileocecal valve Ascending colon Transverse colon Aorta Hepatic portal vein Inferior vena cava Descending colon Sigmoid colon Haustra Tenia coli Circular muscle Longitudinal layer (tenia coli) Intestinal glands Lymphoid nodule Submucosa Muscularis externa Muscularis mucosae

21 The Intestinal Phase: Anatomy of the Large Intestine Figure (1 of 3)

22 The Intestinal Phase: Anatomy of the Large Intestine Figure (2 of 3)

23 The Intestinal Phase: Anatomy of the Large Intestine Figure (3 of 3)

24 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

25 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

26 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

27 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

28 Summary The intestinal phase Brush border, mass movement, and defecation reflex Immune functions M cells and vomiting


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