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Gastrointestinal Physiology

Gastrointestinal Physiology. Dr. Meg- angela Christi Amores. Digestion by Hydrolysis. CARBOHYDRATES Almost ALL in the diet are: large polysaccharides or disaccharides Combinations of monosaccharides H of 1 mono removed, OH of other mono removed = joined H2O is formed

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Gastrointestinal Physiology

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  1. Gastrointestinal Physiology Dr. Meg-angela Christi Amores

  2. Digestion by Hydrolysis • CARBOHYDRATES • Almost ALL in the diet are: large polysaccharides or disaccharides • Combinations of monosaccharides • H of 1 mono removed, OH of other mono removed = joined • H2O is formed • In DIGESTION: reversal of the process • DIGESTION of CARBS: conversion to monosaccharides

  3. Digestion by Hydrolysis • FATS • entire fat portion of diet are triglycerides (neutral fats) • 3 fatty acids + glycerol = triglyceride removing 3 H20 m • in DIGESTION: reversal: • fat-digesting enzymes return three molecules of water to the triglyceride molecule and thereby split the fatty acid molecules away from the glycerol

  4. Digestion by Hydrolysis • PROTEINS • Formed from amino acids linked in peptide bonds • H from one AA removed, OH from another AA removed • In DIGESTION: reversal or process

  5. Digestion • Basic chemistry: • in the case of all three major types of food, the same basic process of hydrolysis is involved • Only difference lies in the types of enzymes required to promote the hydrolysis reactions for each type of food

  6. CARBOHYDRATE Digestion • FOOD in the diet: • 3 major sources of carbs in diet: • Sucrose - ( cane sugar ) • Lactose - ( milk ) • Starch - (all non-animal food, potatoes, grains) • Other carbs: amylose, glycogen, alcohol, lactic acid, pyruvic acid, pectins, dextrins, cellulose

  7. CARBOHYDRATE Digestion MOUTH: Saliva – ptyalin (a amylase) • STARCH --- maltose (di) and polymers of glucose (mo) • Short stay in the mouth, <5% of starch is hydrolyzed STOMACH: gastric juice - acidic • Amylase deactivates in stomach, but can digest about 30-40% while in the fundus

  8. CARBOHYDRATE Digestion SMALL INTESTINE : DUODENUM • Pancreatic amylase – more powerful • 15 to 30 mins of arrival of chyme in duodenum – completely digested • STARCH ------ maltose and glucose polymers JEJUNUM and ILEUM • four enzymes (lactase, sucrase, maltase, and α-dextrinase) • Lactase – GALACTOSE --- lactose and glucose • Sucrase – SUCROSE ---- fructose and glucose • Maltase – MALTOSE --- glucose and glucose

  9. PROTEIN digestion • In the diet: chemically long chains of amino acids bound together by peptide linkages

  10. PROTEIN digestion STOMACH • Pepsin – most active at pH of 2 to 3 (Needs HCl to be activated) • Only initiates digestion (10 to 20% of total protein) • Special ability to digest COLLAGEN • PROTEIN ----- Proteoses, polypeptides

  11. PROTEIN digestion UPPER SMALL INTESTINE • Where most protein digestion occur • Pancreatic enzymes: TRYPSIN, CHYMOTRYPSIN • Proteoses, polypeptides ---- smaller peptides • Pancreatic enzyme: PEPTIDASE (enterocytes) • smaller peptides ----- amino acids

  12. FAT Digestion • In the diet: triglycerides, phospholipids, cholesterol, and cholesterol esters MOUTH, STOMACH • small amount of triglycerides is digested in the stomach by lingual lipase that is secreted by lingual glands in the mouth and swallowed with the saliva (<10%, unimpt) INTESTINE • Where essentially all fat digestion occurs

  13. FAT Digestion • Emulsification by BILE • first step in fat digestion • break the fat globules into very small sizes • begins by agitation in the stomach to mix the fat • most of the emulsification occurs in the duodenum under the influence of bile • Contain BILE SALTS and LECITHIN • to make the fat globules readily fragmentable by agitation with the water

  14. FAT Digestion SMALL INTESTINE • Pancreatic LIPASE • triglycerides of the diet are split by pancreatic lipase into free fatty acids and 2-monoglycerides

  15. ABSORPTION • STOMACH • poor absorptive area, no villi, with tight junctions • Can absorb alcohol, aspirin • SMALL INTESTINE • Absorbs more than 7 L of fluid per day • many folds called valvulaeconniventes (or folds of Kerckring) with villi • intestinal epithelial cell on each villus is characterized by a brush border with microvilli

  16. ABSORPTION – small intestine • Daily: • Several hundred grams of carbohydrates • 100 or more grams of fat, 50 to 100 grams of amino acids, 50 to 100 grams of ions, and 7 to 8 liters of water • ABSORPTIVE CAPACITY: • several kilograms of carbohydrates per day • 500 grams of fat per day • 500 to 700 grams of proteins per day • 20 or more liters of water per day

  17. ABSORPTION • Water – diffusion by laws of osmosis • Sodium – active transport

  18. ABSORPTION • Chloride – diffusion , thru electronegativity created by sodium • Bicarbonates – combine with Hydrogen to form H2CO3 (carbonic acid), which dissociates to form H2O and CO2 . CO2 readily diffuses, released to lungs

  19. ABSORPTION • Carbohydrates • - absorbed in the form of monosaccharides • most abundant of the absorbed monosaccharides is glucose (80%) • galactose and fructose ( 20%) • by secondary active transport • (Glucose co trasported with SODIUM)

  20. ABSORPTION

  21. ABSORPTION • Protein • are absorbed through the luminal membranes of the intestinal epithelial cells in the form of dipeptides, tripeptides and amino acids • Energy supplied by active transport of sodium • co-transport (or secondary active transport) of the amino acids and peptides

  22. ABSORPTION • Fat • end products first become dissolved in the central lipid portions of bile micelles • monoglycerides and free fatty acids are carried to the surfaces of the microvilli of the intestinal cell brush border and then penetrate into the recesses among the moving, agitating microvilli • diffusion

  23. ABSORPTION – large intestine • 1500 mL of chyme enter Large Intestine • Most of the water and electrolytes are absorbed • leaving less than 100 milliliters of fluid to be excreted • Most occur the proximal one half of the colon, giving this portion the name absorbing colon • ABSORPTIVE CAPACITY • maximum of 5 to 8 liters of fluid and electrolytes each day

  24. DIARRHEA • results from rapid movement of fecal matter through the large intestine • Enteritis: inflammation usually caused either by a virus or by bacteria • mucosa becomes extensively irritated, and its rate of secretion becomes greatly enhanced • Cholera – secretion of 10 to 12 liters per day, lead to death. Max abs capacity of LI: 6 – 8L/d

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