Transcript Document
Cell Loss Villous epithelium Blood vessels Lymph vessels Nerves Smooth muscle Connective tissue lymphocytes Plasma cells Eosinophiles Absorptive cells Goblet cells Muscularis mucosa Endocrine cells Crypt lumen Undifferentiated Goblet Mitoses Endocrine cells Crypt epithelium Secretions of the Small Intestine (2000 ml/day) • Crypts of Lieberkuhn: Small and Large Intestine - Contain Primarily Epithelial Cells, Mucus Goblet Cells, and Endocrine Cells. - Water Secretion - VIP Activates Water Secretion by Elevating cAMP and Cl- conductance. - Cell Growth and Differentiation: Cell Turnover at the Tip of a Villus is High (3-6 day Cycle). Crypt Secretion Cl- Na+ cAMP PDte Cl- ? Ca2+ 3 Na+ ATP ADP + Pi 2 K+ H2O Key Players: cAMP Activated Cl- Channel Na+ / K+ / Cl- Co-transport Na-K ATPase Na+ - K+ 2 Cl VIP – neurotransmitter Histamine also can activate Daily Secretions into the Alimentary Canal Daily Volume (ml) • • • • • • • Saliva 1200 Gastric secretion 2000 Pancreatic secretion 1200 Bile 700 Intestinal Secretions 2000 Brunner’s gland secretion 50 (?) Large intestinal secretion 60 • Total 7210 pH 7.0-7.4 1.0-3.5 8.0-8.3 7.8 7.4-7.8 8.0-8.9 7.5-7.8 Cell Loss Villous epithelium Blood vessels Lymph vessels Nerves Smooth muscle Connective tissue lymphocytes Plasma cells Eosinophiles Absorptive cells Goblet cells Muscularis mucosa Endocrine cells Crypt lumen Undifferentiated Goblet Mitoses Endocrine cells Crypt epithelium Sugar Absorption Lactose Starch Glycogen Sucrose a-Amylase LUMEN 30% 70% a-Limit Dextrins Oligosaccharides Glucose Fructose Galactose Na+ Lactase Glucose Na+ a-Dex Glucose Sucrase Glucose Fructose Carrier Glucotrinase Carrier Carrier amylase (Xylose) Brush Border ABSORPTION • Absorption of Nutrients: Carbohydrates - Glucose and Galactose - Sodium Cotransporter Across Luminal Membranes - Fructose - Facilitated Transport (Na+ Independent) - Xylose: Pentose; Uses the Fructose Carrier not Na+ Dependent. Protein Pepsin, Pancreatic Protease Small Peptides Large Peptides Carrier Peptidases Free Amino Acids Neutral Basic Acidic Carrier Mediated Amino Acids Small Peptides Intracellular Peptidases A.A Amino Acids ? Capillary Lipid Digestion and Absorption Large oil droplet (TG) Lipase Co-Lipase Emulsion: TG. MG. FFA. B.S. Micelles MG. FFA. B.S. Microvilli MG. FFA Intestinal epithelial cell Triglyceride Monoglyceride Free fatty acids Pancreatic lipase Glycerol Liver Conjugated bile salts Micelle Ileum FABP Monoglyceride acylation pathway Protein (Apo B) Cholesterol Phosphatidic acid pathway Phospholipids Chylomicron Lacteal Capillary Nutrient Digestion and Absorption -Only Monomers and small digestion products can be absorbed. For amino acids and carbohydrates, most absorption is Na+dependent - Lipids are digested before absorption, then re-synthesized in epithelia cells before packaging and secretion into lymph Glycerol and Monoglycerides diffuse into the blood. Complex fats are packaging into chylomicrons and secreted to the lymph. Lymphatic flow increased 10X during absorption of a high fat meal. Cell Loss Villous epithelium Blood vessels Lymph vessels Nerves Smooth muscle Connective tissue lymphocytes Plasma cells Eosinophiles Absorptive cells Goblet cells Muscularis mucosa Endocrine cells Crypt lumen Undifferentiated Goblet Mitoses Endocrine cells Crypt epithelium Relations Between Salt /Water Secretion and Absorption Net Fluid and NaCl Absorption Villus Epithelia Net Fluid and NaCl Secretion Crypt Epithelia Crypt Secretion Cl- Na+ cAMP PDte Cl- 3 Na+ ATP ADP + Pi 2 K+ H2O Key Player: cAMP Activated CFTR Na+ - K+ 2 Cl Cl- Channel VIP – neurotransmitter Histamine also can activate formation of cAMP Absorption of Na+ Concentration in Chyme: Na+ Conc. K+ Conc. Duodenum 140 mEq/L 5 mEq/L Volume 5 Liters Ileum 125 mEq/L 23 mEq/L 1 Liter Colon (Prox) 40 mEq/L 80 mEq/L 200 mL Absorption of Na+ • Na+ is Absorbed Along the Entire Intestine - Na+ Diffuses Down its Electrochemical Gradient into Epithelial Cells - Luminal Membrane: Co-transport with Nutrients, Diffusion Through Na+ Channels and Na+/H+ Exchange - Transported Across the Basolateral Membrane by the Na-K ATPase. - Cl- Moves to the Blood to Maintain Electroneutrality. Vitamin D3 Liver 25-OH-D3 Kidney Parathyroid Hormone 1,25-(OH)2-D3 RNA Ca2+ CaBP CaBP Intestine Ca2+ Na+ Plasma Ca2+ Ca2+ ATPase Vitamins and Ileal Transport Vitamins Fat Soluble – absorbed all along the intestine via normal fat absorptive pathways. (D, K, A) Water Soluble: Specific Transport Most all along the intestine. Several Ileal Specific- Vitamin: B12 also Ileal Specific: Bile Salts. Absorption of Water - 90-95% of Water (re)absorption in the Small Intestine - 1-2 L/day is Absorbed in the Colon. - A Normal Colon Can Reabsorb a Maximum of About 4.5 liters per day. • Mechanism of H2O Absorption- – Where salt goes, so too does water. Pathophysiology of Diarrhea • The Causes of Diarrhea Delineate into 3 Categories • Motility Based: Limiting Time for Absorption Bacterial Infiltration • Malabsorption; Maldigestion: Osmotic - Lactase Deficiency - Ileal Resection: Biles Salts also stimulate secretion. - Celiac Disease (Sprue; Gluten Sensitive) – Xylose Test • Secretory: Initiated by Effectors which Alter cAMP Levels in Enterocytes; Bile Salts