Small Intestine Anatomy of small intestine o 19 7ft in length o 1 0 diameter o o majority of absorption o 3 sections large surface area duodenum 10 inches jejunum 8 2 feet ileum 11 5 ft ends at ileocecal valve Functions of villi and microvilli o Increase SA for absorption o Brush border enzymes found on surface of microvilli participate in chemical breakdown of carbs and proteins o Cell division within intestinal glands produces new cells that move up Digestion of Carbohydrates o Mouth salivary amylase o Stomach mechanical breakdown o Duodenum pancreatic amylase o Brush border enzymes maltase sucrose and lactase act on disaccharides maltose sucrose lactose Produces monosaccharides fructose glucose and galactose Lactose intolerance no lactase bacteria ferment sugar resulting in gas and diarrhea Absorption of Monosaccharides o Absorption into epithelial cells Glucose and galactose sodium symporter secondary active transporter Fructose facilitated diffusion o Movement out of epithelial cell into bloodstream By facilitated diffusion Digestion of Proteins o Stomach HCl denatures proteins Pepsin turns proteins into peptides smaller AA chains o Small intestine Pancreatic enzymes split peptide bonds between different amino acids Brush border enzymes Aminopeptidase split amino acids at amino end of molecule Dipeptidase split dipeptides Absorption of AA and Dipeptides o Absorption into epithelial cells of duodenum and jejunum Active transport with Na and H ions symporters o Movement out of epithelial cell into blood Diffusion Digestion of Lipids o Mouth o Stomach Lingual lipase Gastric lipase important in infants o Small intestine Emulsification by bile from liver to form micelles Pancreatic lipase splits triglycerides into fatty acids and monoglyceride No lipase enzymes in brush border Absorption of Lipids o Small fatty acids enter absorptive cells and then blood by simple diffusion o Larger lipids are sequestered within micelles after emulsification by bile lipids enter cells by simple diffusion leaving bile salts behind in gut o Bile salts reabsorbed into blood and reformed into bile in the liver o Fat soluble vitamins A K D E are able to enter cells with the lipid o Inside epithelial cells fats are rebuilt and coated with protein to from chylomicrons o Chylomicrons leave intestinal cells by exocytosis into a lacteal Travel in lymphatic system to reach subclavian veins Removed from the blood by the liver and fat tissue Absorption of Electrolytes o Sources of electrolytes GI secretions ingested foods and liquids o Enter epithelial cells by diffusion and secondary active transport Sodium and potassium move by active transport Chloride iodine and nitrate follow passively Ion magnesium and phosphate ions use active transport o Intestinal Ca absorption requires Vitamin D and parathyroid hormone Absorptions of Vitamins o Fat soluble vitamins o Water soluble vitamins Absorbed by diffusion Travel in micelles and are absorbed by simple diffusion with lipids o Vitamin B12 must combine with intrinsic factor from the stomach parietal cells before it is transported into the cells of the ileum Absorbed by receptor mediated endocytosis Absorption of Water o 9L fluid enter GI tract per day o Small intestine absorbs around 8L o Large intestine absorbs 90 of last liter Absorption is by osmosis through cell wal