Digestive Hormones Gastrin family Secretin family Others Gastrin and CCK Secretin family Secretin, VIP, GIP, and GLP-1 Others Motilin PLAY Animation: Digestive System: Control of the Digestive System

THE DIGESTIVE HORMONES Secreted By Target Effects on Motility Stimulus for Release Release Inhibited by Gastrin G cells in stomach parietal cells None Peptides and amino acids in lumen; gastrin releasing peptide and Ach in nervous reflexes pH<1.5; somatostatin CCK Endocrine cells of small intestine; neurons of brain and gut Gallbladder, pancreas, gastric smooth muscle Stimulates gallbladder contraction for bile release; inhibits gastric emptying; promotes intestinal motility Fatty acids and some amino acids Somatostatin Secretin Endocrine cells in small intestine Pancreas, stomach Inhibits gastric emptying Acid in small intestine Gastric Inhibitory Peptide (GIP) Beta cells of endocrine pancreas Glucose, fatty acids, and amino acids in small intestine NA Motilin Smooth muscle of antrum and duodenum Stimulates migrating motor complex Fasting: periodic release every 1.5-2 hours by neural stimulus

Digestion and Absorption A villus and a crypt in the small intestine Figure 21-13

Carbohydrate Digestion: Breakdown to monosaccharide, which can be absorbed Figure 21-14

Carbohydrate Absorption in the Small Intestine Figure 21-15

Enzymes for Protein Digestion Figure 21-16

Peptide Absorption Figure 21-17

Digestion and Absorption Triglycerides digest into monoglycerides and free fatty acids Figure 21-18

Digestion and Absorption of Fats Capillary Cells of small intestine Interstitial fluid Triglycerides + cholesterol + protein Lymph to vena cava Lacteal Golgi apparatus Smooth ER Chylomicron Lumen of small intestine Large fat droplets from stomach Lipase and colipase Emulsion Bile salts recycled Micelles from liver Monoglycerides and fatty acids move out of micelles and enter cells by diffusion. Pancreatic lipase and colipase break down fats into monoglycerides and fatty acids stored in micelles. Chylomicrons are released into the lymphatic system. Absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons. Bile salts from liver coat fat droplets. Cholesterol is transported into cells by a membrane transporter. 1 2 3a 3b 4 5 Figure 21-19

Digestion and Absorption The role of bile salts in emulsions and micelles Figure 21-20

Digestion and Absorption Nucleic acids are digested into nitrogenous bases and monosaccharides Intestine absorbs vitamins and minerals Fat-soluble vitamins (A, D, E, K) absorbed with fats in small intestines Water-soluble vitamins (C, B vitamins) absorbed by mediated transport Exception: Vitamin B12 when complexed to intrinsic factor, secreted in the stomach, and absorbed in ileum Minerals absorbed by active transport

Digestion and Absorption NaCl reabsorption in the small intestine and colon Figure 21-21

Digestion and Absorption Summary of motility, secretion, digestion, and absorption in different regions of the digestive system PLAY Animation: Digestive System: Digestion and Absorption Figure 21-22

3 PHASES OF FOOD PROCESSING Cephalic Phase Gastric Phase Intestinal Phase

The Cephalic Phase Chemical and mechanical digestion begins in the mouth Salivary secretion under autonomic control Softens and lubricates food Chemical digestion: Salivary amylase and some lipase Saliva is protection as well Chewing: mastication

Swallowing Reflex Figure 21-24, step 1

Swallowing Reflex Figure 21-24, step 2

Swallowing Reflex Figure 21-24, step 3

Swallowing Reflex Figure 21-24