gastrointestinal

gastrointestinal - Gastrointestinal Physiology D IGESTION &...

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DIGESTION & ABSORPTION proteins, fats and complex CHO are broken down, digested, principally in the small intestine the products of this digestion, plus the vitamins and minerals cross the mucosa and enter the portal blood or lymph, absorption orderly process, involving a large number of digestive enzymes, originating in the saliva, stomach, SI and exocrine pancreas the action of these enzymes is aided by the action of HCl in the stomach and by bile in the SI the mucosa of the SI has a brush border made of numerous microvilli this is covered by a layer of neutral and amino-sugars, the glycocalyx the membranes of the mucosal cells contain glycoprotein enzymes which hydrolyze CHO and peptides the glycocalyx is made, in part, of the CHO portions of these glycoproteins which extend into the intestinal lumen next to the brush border and the glycocalyx is a 100-400 μ m unstirred water layer (UWL) the mucous coat overlying the mucosa is also a significant barrier to difusion processes involved in the absorption of substances include, a. diffusion b. facilitated diffusion c. solvent drag d. active transport e. secondary active transport f. endocytosis Gastrointestinal Physiology
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Carbohydrates CHO Digestion the principal dietary CHO is composed of, a. polysaccharides b. monosaccharides c. disaccharides starches, polymers of glucose and their derivatives, are the only polysaccharides of importance to humans in glycogen, glucose molecules are joined by 1-4~ linkages, with some chain branching by 1-6 α linkages amylopectin, which ~ 80-90% of dietary starch, is similar but has less branches amylose possesses only 1-4~ linkages and is a straight chain glycogen is found in animals, whereas the later two are of plant origin the disaccharides lactose & sucrose are also ingested, along with the monosaccharides glucose & fructose starch is first degraded by ptyalin, the α -amylase of saliva however, the optimal pH for this is 6.7 and activity is terminated by gastric acidity once in the SI, pancreatic α -amylase is added both of these attack the 1-4 α linkages but spare, a. the 1-6 α linkages b. the 1-4 α linkages next to branch points c. the terminal 1-4 α linkages thus, the end products of this digestion are, a. the disaccharide maltose b. the trisaccharide maltotriose c. larger polymers of glucose with 1-4 α linkages d. branched polymers, ~ 8 units, the α -limit dextrins these are further digested by the oligosaccharidases located at the outer portion of the membrane of the microvilli, a. maltase b. lactase c. sucrase d. α -limit dextrinase in many mammals and some races of humans, intestinal lactase activity is high at birth, declines to low levels in childhood and remains low subsequently Gastrointestinal Physiology
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low levels being associated with intolerance of milk as lactose remains in the GIT and acts as an osmotic agent prior to being broken down by bacteria in the colon however, most Caucasians retain their lactase activity but most adult blacks are intolerant Absorption
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This note was uploaded on 01/16/2012 for the course BI 200 taught by Professor Potter during the Fall '11 term at Montgomery College.

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gastrointestinal - Gastrointestinal Physiology D IGESTION &...

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