dr hameed lecture 17

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gi tract second part


  • 1. Regulation of Intestinal FunctionThe GI has its own nervous system (enteric nervous system), it cansense and form reflex actions due to the presence of food.In the intestine the enteric plexus is very extensive and this is involved inseveral reflexes:1- Gastroilial reflex = increase gastric activity causes increased motility of ileum and movement of chyme (food mixed with digestive juice) through the ileocecal valve.2- Ileogastric reflex =when ileum is distended this decreases the motility andemptyingof the stomach.3- Intestino-intestinal reflex =over-distension of one part of the intestine causes reflexrelaxation of the rest of the intestine.

2. Regulation of Pancreatic SecretionHORMONES :a) Secretin = released from intestinal mucosa in response to presence of acidicchyme in small intestine. Acidic Sodium ChymeBicarbonateIntestinalNeutralizationGlandularMucosal Cells ofCellPancreasSecretin Blood Disfunction of the above may cause duodenal ulcer. 3. Regulation of Pancreatic SecretionHORMONES :b) CCK = released mainly in response to presence of fat, proteins andcarbohydrates in small intestine. FattyDigestive ChymeenzymesIntestinal DigestionGlandularMucosal Cells ofCellPancreas CCKBlood 4. Gallbladder EmptyingThe bile is secreted by the liver and stored in the gallbladder. Both secretin and CCKstimulate secretion of bile by the liver. CCK is major stimulator of gallbladder contraction.Neural reflexes also help with gallbladder contraction and bile release into duodenum.VagusLiver ACh + CCK Gallbladder +PancreasCCK FAT Duodenum ... CCKBlood 5. Digestion and AbsorptionFood mainly contains: Carbohydrates mainly polysaccharides (starches) and disaccharides. Lipids (fat) mainly triglycerids Proteins polymers of amino acidsAlso in small amounts food contains: - Nucleic acids, DNA and RNA - Salts and minerals, Na, Cl, Ca, Fe, PO4, Cu, etc. - Vitamins, C, D, Thiamin (B1), Riboflavin (B2), B12 etc. 6. DigestionDigestion = breaking down of large compounds in food into smaller and simplersubstances that can be absorbed and used by the cells of the body. 7. = glucoseCarbohydrates in Food = fructoseMost common carbohydrates ingested are:= galactose - Starch long chain of glucose (polysaccharides) with occasional branching. - Sucrose (table sugar) a disaccharide consist of glucose and fructose.- Lactose (milk sugar) a disaccharide consist of glucose and galactose. 8. Lactose Intolerance Deficiency in enzyme lactaseInadequate lactose digestion(Lactose in milk)High level of lactose in intestine (Colon)Osmotic effect (water moves Bacterial action onfrom blood to lumen)undigested lactose. Intraluminal volume and gas DIARRHEOA & GAS 9. Digestion of Carbohydrates- The digestion of carbohydrates occur in mouth and it continues in the duodenum. 10. Digestion & Absorption of Carbohydrates- Short oligosaccharids (-limit dextrins), maltotrios and maltose are broken down tosingle sugars (monosaccharides) by the brush border enzymes.- The resulted monosaccharides are : Glucose (80%) Fructose (10%) Galactose (10%)-The monosaccharides (glucose & galactose) are transported into epithelial cells bysecondary active transport and fructose is transported by facilitated diffusion.FructoseNa+ Glucose Intestinal Lumen Fructose K+GlucoseNa+Blood 11. Digestion of Proteins- Proteins are polymeres of amino acids, they can be formed from less than 100 aminoacids up to thousands.-There is no digestion of proteins in mouth, the digestion starts in the stomach by the action of pepsin. pepsinogenChief cellsPepsin in the stomachProtein Polypeptides + amino acids- Most protein digestion occurs in duodenum and jejunum. Pancreatic enzymesFood fromthe stomachDuodenum (small intestine) 12. - Pancreatic enzymes areactivated in the duodenumby the action of enterokinase. Enterokinase 13. - Final Products ofprotein digestion are: Amino acids, Dipeptides and Tripeptides. 14. Absorption of Proteins- There are five different transport systems for protein digestionproducts:Neutral amino acidsAcidic amino acidsSecondary active transportIMINO acidsBasic amino acidsFacilitated diffusionDi- and Tri-peptides Tertiary active transport 15. Digestion of Lipids- For their digestion, lipids must be first emulsified.- The bile secreted into duodenum combines with lipids and reduces theirsurface tension breaking the lipids into small droplets. 16. Digestion of Lipids 17. Micelles Formation and Absorption 18. Absorption of Lipids 19. Absorption of Water- Approximate daily intake = 2 L- Approximate GIT secretion each day = 7 L- Only 50 to 100 ml/day is excreted in the feces.