fourth test notes

fourth test notes - I. Digestion A. Digestive tract is...

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I. Digestion A. Digestive tract is 17-20’ tube (mouth to anus) B. Mouth 1. Both mechanical and chemical digestion occurs 2. Saliva contains amylase which breaks down starch and lipase which breaks down fats a) Also has lysozyme - antibacterial enzyme that lyses bacteria 3. Parasympathetic stimulates salivation, strong sympathetic inhibits (cottonmouth/dry mouth) 4. Food odors and some foods especially sour/dry (crackers, lemon, pickles) stimulate salivation C. Stomach 1. Stomach mixes food and gastric secretions to form chyme ; denatures proteins, disinfects 2. Cells lining stomach produce a thick protective mucus 3. Gastric pits secrete a variety of substances a) Mucus cells produce a watery mucus b) Chief cells produce pepsinogen which is converted to pepsin (1)Pepsin breaks down proteins into small peptides c) Parietal cells secrete HCl at a pH of 1 (1)Their proton (H+) pump can pump against a million times gradient (a) Inhibited by Prilosec and other (2)Strong acid is a good solvent, disinfectant and denatures protein (means it breaks the tertiary and quadriary bonds so enzymes can enter) d) G cells of gastric pits secrete gastrin into bloodstream 4. Stomach absorbs some small molecules: ETOH, H2O, glucose, especially non-polars 5. Lining of the stomach is replaced roughly every 3 days 6. Intrinsic factor - polypeptide produced by parietal cells that facilitates absorption of vitamin B12 in Small intestine D. Small intestine or duodenum 1. About 10’ long; absorptive area is size of tennis court a) Highly folded, covered with finger like villi (1)Each villi is vascularized and covered by microvilli b) Surface cells turn over every few days c) Capillaries in villi absorb nutrients (1)Lacteals (lymphatic capillaries) absorb fat (2)Fat is first absorbed and carried by lymph vessels 2. Takes several hours for chime to move through Small Intestine E. Pancreas 1. Connected to Small Intestine via pancreatic duct 2. Secretes a complete set of digestive enzymes a) Amylases break down carbos b) Lipases break down fats
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c) Proteases break down proteins 3. Produces bicarbonate to stomach acid 4. Neutralize SI microvilli secrete enzymes to perform final breakdown of food to small absorbable molecules F. Liver 1. For fat digestion, fat must first be emulsified by bile (has detergent properties) from the liver a) Liver constantly produces bile; which is stored in the gall bladder (1)After meals, gall bladder contracts sending bile to small intestine b) Emulsification increases surface area for lipases to break down fat (1)Components are taken into lacteals of villi and eventually go into bloodstream (a) Fatty meal: serum of plasma of spun down blood appears cloudy G. Large Intestine = Colon 1. About 4 feet long 2. Large intestine absorbs 0.5-2.0 liters of water a day; Na+, vitamins, drugs, suppositories a) Secretes K+ 3. Slow movement lets bacteria digest unabsorbed material (mostly cellulose) (= fiber) a) 1/3 mass of feces is of bacterial origin b) Bacteria produce gas =
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This note was uploaded on 02/10/2011 for the course BIO 1500 taught by Professor Maruniak during the Fall '08 term at Missouri (Mizzou).

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fourth test notes - I. Digestion A. Digestive tract is...

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