Wednesday May 20 2015 6 00 PM Gastrointestinal tract o Pathway for ingested food o Mouth pharynx esophagus stomach small intestine large intestine o Function of GI Digestion hydrolysis of energy nutrients Absorption passage of simple molecules across the gut wall into the blood or lymph Oral cavity o Mastication chewing breaks down food in order to increase surface area o Saliva Contains enzymes Salivary amylase Digests carbs Salivary lipase digest milk fat lipase Lysozymes Contain digestive enzymes to kill bacteria First line of defense Begins in mouth and continues to stomach along with gastric Esophagus o Muscular tube that connects back of the mouth and stomach Moves food by peristalsis o Lower esophageal sphincter Circular muscular valve that relaxes to let food into stomach and constricts to keep food from moving back up into esophagus Esophagus needs this to complete peristalsis o GERD gastro esophageal reflux disease Due to reflux of digestive juices from stomach to esophagus due to relaxation of lower esophageal sphincter Stomach acid comes in contact w esophagus Possible causes include Spicy foods caffeine fatty foods and pregnancy Over time it can damage esophagus which leads to esophageal ulcers and o Holds and digests food by mechanical mixing breaking down of food and gastric risk of esophageal cancer Stomach secretions o Also absorbs alcohol aspirin o Relays messages like fullness and satiety o Gastric secretions Gastrin peptide hormone produced by G cells in stomach lining As gastrin levels rise the stomach releases gastric acid and HCL which helps digest and break down food Release of HCL and pepsinogen Hydrochloric acid HCL released by parietal oxyntic cells and is used to activate pepsinogen Kills bacteria Denatures proteins so pepsin can digest them Converts pepsinogen into pepsin Inactivates lingual lipase Pepsinogen secreted by chief cells in response to acetylcholine It is a zymogen inactive protein digesting enzyme Inactive precursor to pepsin Aids in protein digestion Mucus Protects stomach lining Contains bicarbonate which prevents blood from becoming too acidic What alka seltzer is Intrinsic factor Necessary for absorption of B12 B12 is important for neurological functioning Pyloric sphincter Small intestine o Circular muscular valve that separates stomach from duodenum o Regulates movement of food and acid from stomach to small intestine o Chyme food acid o Sections include the duodenum most important jejunum and ileum o Duodenum Main site of digestion and absorption and receives secretions from other digestive organs such as the pancreas and gall bladder Folded into finger like projections that house blood and lymph called villi which increase the surface area of the intestine Lining Villi is covered with microvilli which further increases the surface area of the intestine Microvilli is known as the brush border Brush border is where the digestion of nutrients usually occurs Enterocytes Cells that line the villi Villar tip cells where most absorption occurs Mid villar cells secrete digestive enzymes and hormones Enzymes for macronutrient digestion Hormone CCK secretin GIP CCK cholecystokinin Secreted in duodenum and is synthesized by I cells in small intestine Causes the release of digestive enzymes and bile from the pancreas and gallbladder respectively Also is a hunger suppressant Secretin Regulates water homeostasis throughout body and regulates secretions in the stomach and pancreas Releases bicarbonate from pancreas to lower pH Inhibits gastric emptying and motility GIP Glucose dependent insulinotropic peptide Acts to inhibit gastric emptying and motility but also stimulates insulin secretion by acting on alpha cells o o Jejunum Ileum Digestion and absorption continues Absorption Enterohepatic circulation of bile after the digestion of fats bile is reabsorbed in the ileum and sent back to the liver and is dispersed around the body Large intestine Part of the vascular system o Smooth lining no villi part of GI that absorbs water and electrolytes along with eliminating wastes o Temporary storage and concentration until defecation o Intestinal microflora Bacterial breakdown of fiber Produce vitamin K and some B vitamins Accessory organs o Pancreas Acini secrete enzymes into GI tract They are stimulated by CCK and secretin Inhibited by peptide YY and somatostatin Zymogens inactive enzymes for the hydrolysis of proteins and smaller peptides to amino acids Pancreatic amylase hydrolysis of starch to oligosaccharides Dextrin maltose and maltoriose Pancreatic lipase hydrolysis of triacyglycerols TAG to monglycerols MAG fatty free acids FFA and glycerol Basically it is a water soluble enzyme that breaks down lipids fats It differs from other enzymes because it can break dietary fats down via hydrolysis by breaking hydrogen bonds Islet tissue Secrete hormones into blood Beta insulin Alpha glucagon Delta somatostatin Not connected to GI o Liver command center of metabolism Makes bile Emulsifier for fats to increase the surface area of fats and is required for fat digestion Made in hepatocytes from cholesterol and is stored in gallbladder After digestion of fats bile is reabsorbed in ileium and sent back to the liver Metabolizes drugs alcohol and other toxins Makes plasma proteins Site of urea synthesis Albumin major transport protein that maintains osmotic pressure Low levels allow for fluid to leave the blood stream and pool in intercellular spaces Liver damage affects this Transferrin transports iron Lipoproteins carry various lipid cholesterol components to tissues Chylomicron VLDL IDL LDL and HDL LDL and HDL are proteins that carry cholesterol LDL from liver to tissues HDL from tissues to liver o Circulation of nutrients Vascular system disperses it to body Lymph system Enterohepatic circulation carries nutrients in blood to liver and then Exogenous lipid transport Removes and destroys waste Absorbs fat and fat soluble vitamins and delivers them to cells that Removes excess fluid and waste products from the interstitial spaces need them between the cells Carbohydrates Major source of energy fuel in the average diet Approximately of total caloric intake in the form of Polysacchardies Starches and dextrins Simple sugars Sucrose lactose fructose Chemical structure CH2O Simple lyceraldehyde Monosaccharides or disaccharides Complex glycogen Oligosaccharides or polysaccharides Where we store glucose Monosaccharides Types 3 triose 4 tetrose 5 pentose 6 hexose
View Full Document
Unlocking...