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Biol 216 12 UPDATED Digestion 49-93.pdf

Biol 216 12 UPDATED Digestion 49-93.pdf - Stomach-Acidic...

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5/30/17 1 Stomach-Acidic pH=2 à optimal pH for pepsin Helps unfold proteins so they can be broken down Kills unwanted bacteria Stomach’s mucus protects stomach wall from acidity and breakdown from pepsin 5/30/17 49 Stomach Can take 1-6hrs for the stomach to empty after a meal Food is not moved along faster than it can be digested Fat: is digested in small intestines and is digested more slowly than other nutrients, so further emptying of the stomach is prevented until fat is processed 5/30/17 50 Digestion in small intestine Most digestion occurs here Proteins – broken down by endopeptidases, exopeptidases Polysaccharides – hydrolyzed by amylase, then disaccharidases Triglycerides hydrolyzed by lipase Nucleic Acids hydrolyzed by nucleases (DNase, RNase) 5/30/17 51
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5/30/17 2 The Digestive Process Absorption of nutrients begins in the small intestine Specializations to optimize absorption Intestinal villi: folds in lining of small intestine Microvilli: projections of plasma membrane of epithelial cells Villi and microvilli greatly increase the surface area of intestine 5/30/17 52 Villi in the Small Intestine 5/30/17 53 Fig. 45.11a, p. 1028 Folds of small intestine Section of small intestine Villus 5/30/17 54
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5/30/17 3 Brush border Capillaries Microvilli Intestinal epithelial cell Lymphatic vessel Villus 5/30/17 55 Nutrient Absorption in the Small Intestine 5/30/17 56 The Digestive Process- Small Intestine In the duodenum, digestive juices from the pancreas and liver add enzymes and digestive aids to the food mass Pancreas secrete digestive enzymes and bicarbonate ions (HCO3-: neutralize acidity) into ducts that empty into the duodenum CO2+H2O ó H2CO3 ó HCO3- + H + 5/30/17 57
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5/30/17 4 Basic fluid: high concentration of bicarbonate ions(HCO 3 - ) Proteolytic Enzymes: trypsin chymotrypsin, carboxypeptidase Lipase Amylase Nucleases From the Pancreas Bicarbonate ions neutralizes the pH of the chyme for optimal activity of amylase, proteases, lipases, nucleases. 5/30/17 58 From the pancreas-Hormones Glucagon (alpha cells): is released when blood glucose levels start to fall too low Causes the liver to convert stored glycogen into glucose and release it into the bloodstream, raising blood glucose levels. Insulin (beta cells): causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, Storing it as glycogen in the liver and muscle, and stopping use of fat as an energy source. 5/30/17 59 Digestive Enzymes 5/30/17 60
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5/30/17 5 Fat digestion: small intestine Liver secretion bile (bile is a mixture of substances that act as emulsifiers) à emulsifies fats Emulsify: combine two components that usually don’t combine easily (oil-water) Eg., Salad dressing, mayonaise Bile salts: aid in fat digestion by forming a hydrophillic coat around fats.
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