GI Tract HUN3224 Most of immune system is in GI tract Oral Cavity o Mastication chewing breaks down food Increases surface area o Saliva Enzymes Lysozymes Kill bacteria Our first defense Esophagus Salivary amylase carbs Salivary lipase milk fat most active in infants o Muscular tube connect the back of the mouth and stomach Movement of food via peristalsis o Lower esophageal sphincter circular muscular valve Relaxes to let food into stomach Constricts to keep food from moving back up into esophagus o GERD gastro esophageal reflux disease Relaxation of LES weak LES Stomach acid comes in contact with esophagus Possible causes spicy foods caffeine fatty foods pregnancy pressure from obesity laying down after eating etc Over time can damage esophagus leading to ulcers and an increased of esophageal cancer Stomach o Holds food o Mechanical mixing and breaking down of food o Gastric secretions Gastrin Release of HCl and pepsinogen Hydrochloric Acid HCl Kill bacteria Denatures proteins Inactivates lingual lipase Converts pepsinogen into pepsin Pepsinogen Inactive precursor to pepsin all proteases are inactive at rest Protein digestion Mucus Intrinsic Factor Protects stomach lining Contains bicarbonate to neutralize acid Necessary for absorption of B12 Lack of B12 anemia lethargy etc o Absorption of alcohol and aspirin Pyloric Sphincter o Circular muscular valve separating stomach from duodenum o Regulates movement of food and acid from stomach to small intestine o If it does not work properly dumping diarrhea o Chime food acid Small Intestine o 3 sections Duodenum Main site of digestion and absorption Receives secretions from other digestive organs pancreas gallbladder Lining folded into finger like projections called villi o Increases surface area increases absorption o Villi covered with microvilli o Microvilli brush border where digestion is usually completed o Villi are lined with enterocytes gate keepers Villar tip cells slough off the tip Midvillar cells secrete digestive enzymes hormones for macronutrient digestion CCK secretin GIP Crypt cells replicate bottom Jejunum Digestion and absorption continue longest section Ileum We reabsorb most bile Absorption Enterohepatic circulation of bile o Smooth lining no villi o Water and electrolyte absorption o Intestinal microflora bacterial breakdown of fiber produce vit K and some B vitamins When we are born we get a shot of K helps us produce bacteria in gut o Temporary storage and concentration until defecation Large Intestine Accessory Organs o Pancreas Acini secrete enzymes into GI tract Zymogens Pancreatic amylase Pancreatic lipase Islet tissue Secrete hormones into blood o Beta insulin o Alpha glucagon o Delta somatostatin Not connected to GI Shares common bile duct with gallbladder gallstone back system up pancreatitis imbalance of blood glucose o Liver Makes bile Emulsifier for fats needed for fat digestion Bile o Made in hepatocytes from cholesterol o Stored in gallbladder o After digestion of fats bile reabsorbed in ileum and sent back to liver EHC Metabolizes drugs alcohol and toxins Urea synthesis Makes plasma proteins Transport proteins maintains osmotic pressure low albumin fluid pools o Albumin in intercellular spaces edema various lipid cholesterol components to tissues transports iron o Transferrin o Lipoproteins 5 types chylomicron VLDL IDL LDL HDL carries Circulation of Nutrients o Vascular System o Lymph System Carries nutrients in blood to liver and then disperses it to body EHC For water soluble substances Exogenous lipid transport Lacteals fat fat soluble substances go through these Fat directly into bloodstream
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