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77 Cards in this Set
- Front
- Back
Most carbohydrates of the diet are…
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large polysaccrides or disaccharides
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Process of separating poly/disaccharides
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hydrolysis
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Most fats in diet are…
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triglyccerides
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What are triglycerides composed of
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glycerol plus fatty acids
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3 major sources of carbohydrates
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sucrose, lactose, starches (others: amylose, glycogen, alcohol, lactic acid, pyruvic acid, pectins, dextrins, carbohydrate derivatives in measts)
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What enzymes does saliva contain
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ptyalin (alpha-amalase secreted by parotid glands);
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No more than what percent of food is hydrolyzed in the mouth
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5%
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How long can food continue digesting in stomach before mixing with gastric secretions
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1 hour
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What pH does salivary amalase become inactive
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4
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how much starch is hydrolyzed before mixing with gastric secretions
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as much as 30-40%
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How long does it take for starches to be completely hydrolyze once entering duodenum
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15-30 minutes (pancreatic amalase is several times more powerful)
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What enzymes do the enterocytes lining villi of small intestine contain?
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lactase, sucrase, maltase, and alpha-dextrinase
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What makes up lactose
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glucose and galactose
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what makes up sucrose
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fructose and glucose
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How are monosaccrides absorbed
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fdirectly into portal blood
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monosaccride breakdown percents once digested
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glucose 80%, galactose and fructose each around 10%
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What secrets HCl
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parietal (oxyntic) cells (pH of 0.8 when first secreted, then 2-3 when mixed in stomach)
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Major constituent of intercellular CT of meat
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collagen; broken down by pepsin (must be broken down before other proteins an penetrate meat)
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Where does most digestion occur
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upper small intestine in duodenum and jejunum
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pancreatic enzymes that act on chyme entering duodenum
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trypsin, chymotrypsin, carboxypeptidase, proelastase
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what does carboxypeptidase do
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cleaves individual aas from carboxyl ends of polypeptides
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What do trypsin and chymotrypsin do
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split protein molecules into small polypeptides
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Most proteins get digested down to…
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dipeptides and tripeptides
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where are peptidases located
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brush border microvilli membranes
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Two types of peptidase enzymes that are especially important
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1) aminopolypeptidase 2) several dipeptidases (split remaining polypepetides into di and tri pieces)
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Where are di and tripeptides transported
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through microvillar membrane into interior of enterocyte
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Where are most peptides split into individual aas
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in cystol; they pass into blood once formed
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Fat digestion in stomach
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small amount by lingual lipase (from saliva); less than 10% fat digestion
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Where does emulsification begin
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in stomach with agitation to mix food/fat with products of digestion
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Most emulsification occurs where
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in duodenum with bile (bile salts plus lecithin)
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What is the purpose of bile
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emusification; reduces interfacial tension of fat and makes it soluble
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average diameter of fat after emulsification
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~1 um; 1000-fold increase in SA
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Most important enzymes for digesting triglycerides
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pancreatic lipase (enough released to digest everything it can reach in 1 minute); enterocytes also have lipase, not usually needed
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What transports fatty acids to prevent reversal of digestion
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bile salts (remove monoglycerides and free fatty acids)
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Bile salt micelle specs
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3-6 um with 20-40 molecules; ferries
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Cholesterol esters
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combination of cholesterol and one fatty acid molecule; most common dietary cholesterol
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quantity of fluid absorbed by intestines each day
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1.5 L from ingested fluid and 7 L of GI secretions
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How much fluid is absorbed in small intestines
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all but 1.5 L
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What substances can be absorbed through the stomach
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high lipid-soluble substances like alcohol and aspirin in small quantities
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folds that increase the suface area in small intestine
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valvulae conniventes; increase SA 3 fold
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where are the folds most developed
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duodenum and jejunum; protrude as much as 8 mm into lumen
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How far do villi project from suface of mucosa
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~1 mm; increase SA 10 fold
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how much do microvilli increase SA
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at least 20 fold
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Organization of villus
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1) vascular system to absorb 2) central lacteal
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daily absorption from small intestine
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several hundred grams carbs, 100+ grams fat, 50-100 grams aas, 50-100 grams ions, 7-8 L water
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absorption capacity of small intestine per day
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serveral kg of carbs, 500 g fats, 500-700 g proteins, 20+ L water
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What can the large intestine absorb
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additional water, ions, very few nutrients
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How is water transported
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entirely through diffusion
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Sodium absorption/use in body
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20-30 g secreted into intestine, 5-8 g eaten; must absorb 25-30 g (1/7 of all body sodium)
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What percent of intestinal sodium passes into feces
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less than 0.5%; important in absorbing sugars and aas
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Na+ in intestinal epithelial cells
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1) transported actively into paracellular spaces 2)Cl- atoms follow Na+ 3) Na+ concentration in cells low (50mEq/L) 4)Na+ concentration in chyme ~142 mEq/L 5) Na+ follows gradient into cells
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How does aldosterone affect Na+
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within 1-3 hours of release, increases activation of enzyme and transport mechanisms for all aspects of Na+ absorption in intestinal epithelium
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Increased Na+ absorption causes…
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secondary increase in Cl- and water absorption (plus some other substances)
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Cl- ion absoprtion
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rapidly absorbed in upper small intestine; fixes the electronegativity in chyme/electropositivity in paracellular spaces created by Na+
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Bicarb absorption in small intestine
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1) when Na+ absorbed, moderate amount of H+ secreted into lumen 2) H+ combine with bicarb to form H2CO3 3) dissociated into water and CO2 4) water stays in chyme, CO2 absorbed directly into blood and expired in lungs
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Bicarb secretion in ileum and large intestine
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epithelial cells secrete bicarb in exchange for Cl-; neutralizes acid products formed by bacteria
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Flow of water in large intestines
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young/immature epithelial cells secrete NaCl into lumen which is reabsorbed by older/mature epithelial cells
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How does cholera and other diarrheal bacteria cause their effect
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stimulate fold secretion/young epithelial cells so greatly, old cells can not absorb quickly enough
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What specifically causes oversecretion with cholera
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formation of excess cyclic adenosine monophosphate, which opens large numbers of Cl- channels
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How are Calcium ions absorbed
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actively by duodenum; controlled by PTH and vit D
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Monovalent vs divalent ion absorption
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monovalent ions absorbed with ease in great quantities, divalent absorbed in small amounts
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Glucose absorption
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sodium co-transport mechanism (secondary active transport); facilitated diffusion into blood from epithelial cells
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Galactose absoption
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almost same as glucose (secondary active transport with Na+)
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Fructose absorption
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facilitated diffusion all the way through intestinal epithelium; transport rate 1/2 of glucose and galactose
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peptide/aa absorption
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most through Na+ co-transport; a few only use facilitated diffusion; at least 5 types of transport proteins for aa and peptides have been found
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lipid absorption
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transported by micelles and are immediately absorbed into epithelial cell membrane
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How much fat can be absorbed without/with bile micelles
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40-50 % versus 97%
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What happens to lipids once in epitheial cytoplasm
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taken up by smooth ER and used to make new triglycerides which are released as chylomicrons into lymph and go to thoracic duct
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Why so some lipids absorb directly into portal blood
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short and some medium chain fatty acids are water soluble and absorbed directly
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How much chyme enters colon each day
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1500 mL; most absorption in proximal 1/2 of colon
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tight jxns in large vs small intestine
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much tighter in large intestine; prevents back-diffusion of ions
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What causes osmotic gradient for water absorption in large intestine
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absorption od Na+ and Cl- ions
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max absorption of colon
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5-8 L of fluid and electrolytes/day
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Fxn of bacteria in colon
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1) digest some cellulose 2) vit K, vit B12, thiamine, riboflavin production 3) flatus (CO2, H2, and methane)
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composition of feces
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3/4 water 1/4 solid matter
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Solid matter composition of feces
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30% dead baccteria, 10-20% fat, 10-20 organic matter, 2-3% protein, 30% undigested roughage
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What causes brown color of feces
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stercobilin and urobilin (derivatives of bilirubin)
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