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42 Cards in this Set
- Front
- Back
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What are the monosaccharides? |
glucose, galactose & fructose |
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What are the disaccharides? |
lactose, sucrose & trehalose |
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What are the polysaccharides? What are they broken down into? Name the disaccharides & monosaccharides involved |
Starch initially digested into disaccharides: alpha-dextrins, maltose, maltotriose Disaccharides are then digested into monosaccharide: glucose |
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What is trehalose & what is it digested into? |
Disaccharide that is digested into glucose |
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What is sucrose & what is it digested into? |
Disaccharide that is digested into fructose & glucose |
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What is lactose & what is it digested into? |
Disaccharide that is digested into glucose & galactose |
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How are monosaccharides transported across the apical membrane of the small intestine? (differentiate btw each monosaccharide) |
Glucose & galactose are transported across the apical membrane by the SGLT 1 transporter (Na+-glucose/galactose symport; secondary active transport) Fructose crosses the apical membrane through the GLUT5 channel (facilitated diffusion) |
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How are monosaccharides transported into the blood across the basolateral membrane of epithelial cells in the small intestine? |
GLUT2 channels (facilitated diffusion) |
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Where are carbohydrates digested? What enzymes are needed for their digestion? |
Digestion begins in the mouth: salivary alpha-amylase Digestion also occurs in the small intestine by pancreatic alpha-amylase Only monosaccharides can be absorbed |
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What causes lactose intolerance? |
There is a problem w/ lactate being digested into glucose/galactose. Lactose cannot be absorbed into the blood stream until it is broken down into monosaccharides. Accumulation of lactose in the small intestine acts as an osmotically active solute and leads to osmotic diarrhea |
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What are proteins digested into? |
amino acids, dipeptides & tripeptides |
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Where does protein digestion occur? What enzymes are involved? |
Protein digestion occurs in the stomach & small intestine. Stomach: pepsinogen is converted to pepsin due to a low pH; pepsin is the active form that breaks down proteins Small intestine: pancreatic & brush boarder proteases break down protein |
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How are pancreatic proteases activated? |
a small amount of trypsinogen is converted to trypsin by enterokinase in the sm. intestine trypsin produced from above rxn is used as the enzyme to covert all other proteases (pro-enzymes) to their active forms to digest protein proteases in active form: trypsin, chymotrypsin, elastase, carboxypeptidase A, carboxypeptidase B |
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What enzymes are required for protein breakdown in the small intestine? |
enterokinase & trypsin enterokinase is needed to produce trypsin |
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How are protein digestion products transported into the blood? |
amino acids: Na+ - amino acid cotransport (secondary active transport) on apical membrane Dipeptides/tripeptides: H+ - peptide cotransport (secondary active transport) on apical membrane In epithelial cell of small intestine: dipeptides & tripeptides are converted to amino acids by peptidase Amino acids then diffuse out of the epithelial cell and into the blood |
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What is the common cause of disorders of protein digestion/absorption? |
Disruption of pancreatic enzymes; e.g. chronic pancreatitis or cystic fibrosis disorders of transporters for amino acids, dipeptides & tripeptides |
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What are the dietary lipids? |
triglycerides, cholesterol & phospholipids |
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Where does the digestion of lipids occur? |
lingual lipases & pancreatic lipases (digestion in small intestine) |
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What are the enzymes in the small intestine that digest lipids? |
pancreatic lipases, cholesterol ester hydrolase & phospholipase A2 |
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What are triglycerides digested into? |
a monoglyceride & 2 fatty acids |
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What is cholesterol ester digested into? |
fatty acid & cholesterol |
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What are phospholipids digested into? |
lysolecithin & fatty acid by phospholipase A2 |
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What hormone plays an important role in lipid digestion in the small intestine and why? |
CCK slows the rate of gastric emptying of chyme to give adequate time to digest lipids in the sm. intestine; stimulation of CCK secretion is stimulated by the first appearance of lipids in the small intestine |
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How are lipids broken down? What increases the rate lipids can be broken down? |
Lipids are poorly soluble in water; they must be broken down into small droplets to be effectively digested by enzymes; bile salts stabilize the small lipid droplets forming micelles bile salts increase rate of lipid digestion |
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How are lipids absorbed? What are micelles? What happens to lipids once they are in the epithelial cells of the small intestine? How do they get out? |
Micelles have a combination of lysolecithin, fatty acids, monoglycerides, & cholesterol all stabilized by bile salts released from the gall bladder Micelles are found next to brush boarder; contents leave micelles & diffuse across apical membrane of epithelial cells small components of lipids inside of epithelial cells reform cholesterol ester, triglycerides & phospholipids; they cannot diffuse freely across basolateral membrane so they are coated w/ apoproteins and re-esterificated smooth ER: lipid-protein vesicles are called chylomicrons which diffuse across basolateral membrane into lacteals of the lymph system |
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Where do the chylomicrons go? |
Chylomicrons travel through lymph system to cardiovascular system; they empty into the thoracic duct |
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What causes disorders of lipid digestion? |
Pancreatic insufficiency; low pH in sm. intestine, Zollinger-Ellison syndrome (excessive secretion of gastrin); inadequate secretion of HCO3- from pancreas; deficiency of bile salts; bacterial overgrowth, tropical sprue; failure to synthesize apoproteins for chylomicron formation |
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What are the fat solute vitamins? How are they absorbed into the blood? |
Vitamin D, E, A, K Incorporated into micelles w/ lipids & diffuse across apical membrane; they are reincorporated into chylomicrons & enter lymphatic system |
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What are the water soluble vitamins? How are they transported into circulation? |
Vitamin: B1, B2, B6, B12, C, biotin, nicotinic acid & pantothenic acid all are transported through Na+ - dependent transport except B12 which is transported by intrinsic factor secreted by parietal cells in the body of the stomach |
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What is cobalamin? |
Vitamin B12 |
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How is vitamin B12 absorbed? |
in the stomach, B12 binds R proteins/haptocorrin; these R proteins are degraded in the duodenum by proteases & transferred to intrinsic factor; in the ileum B12-intrinsic factor complex is transported across epithelial cells |
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What is required for Ca2+ absorption? |
Vitamin D: active form is Vit D3/dihydroxycholecalciferol Vit D3 required for Vit D-dependent Ca2+ binding protein or calbindin D-28 K Vit D-dependent Ca2+ binding protein required for transport of Ca2+ into epithelial cells of small intestine |
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What diseases are associated w/ Ca2+ deficits? |
Rickets in children Osteomalacia in adults causes soft/brittle bones |
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How is iron absorbed? |
Absorbed as free oxidized iron Fe3+/heme iron; in epithelial cells Fe3+ binds apoferratin & transported across basolateral membrane into circulation; once in circulation, Fe3+ binds transferrin & is transferred to liver for storage |
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How are water & electrolytes absorbed in the small intestine? |
transcellular & paracellular; "leaky junctions" paracellular secretion of water & Na+ Na+ is absorbed w/ amino acids from protein digestion or sugar from carbohydrate digestion |
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What transport processes occur in the jejunum? |
Na+ - amino acid ATPase pump Na+ - H+ counter transport; H+ being secreted into lumen of jejunum & Na+ absorbed In epithelial cells CO2 + H2O form bicarb and H+; H+ is secreted and bicarb is absorbed into blood stream |
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What transport processes occur in the ileum? |
Apical membrane: Na+ - amino acid ATPase pump Na+ - H+ counter transport like in jejunum but there is also a bicarb- Cl- counter transport; bicarb is secreted into the ileum to buffer the H+ being secreted *opposite of jejunum since bicarb is going into the lumen rather than the blood stream Basolateral membrane: Cl- absorption Amino acid/sugar absorption |
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What transport occurs in the colon? |
ENaC channels on apical membrane stimulated by aldosterone; some K+ being secreted "tight junctions"; no paracellular transport |
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Where/how does chloride secretion occur? |
occurs in epithelial cells lining the intestinal crypts; only channel on the apical boarder is a Cl- channel; this channel is typically closed Cl- channel on apical membrane opened by ACh & VIP basolateral membrane has tritransporter Na+ - K+ - 2Cl-; transports these three things simultaneously into the epithelial cell of crypt |
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How do Cl- channels on apical membranes of crypts in small intestine open? |
There is a GPCR on the basolateral membrane of the epithelial cell of the crypt; ACh & VIP can activate this GPCR; once activated adenylyl cyclase is activated which increases cAMP to enhance the opening of the Cl- channel on the apical membrane allowing Cl- secretion |
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What effect does cholera have? |
Cholera enters the epithelial cells through the lumen and acts at the GPCR on the basolateral membrane of the epithelial cells in the crypts of the small intestine; it produces a sustained activation of the GPCR causing substantial Cl- secretion drawing water into small intestine can cause severe dehydration & eventually cardiovascular collapse |
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What is diarrhea caused by? What are the forms of diarrhea? |
Osmotic diarrhea: due to an osmotically active substance in the lumen drawing water into lumen; caused by lactase deficiency & lactose retention Decreased absorptive surface area: can cause diarrhea: this can be due to infection or inflammation of the sm. intestine Secretory diarrhea: secretion of a solute e.g. cholera toxin usually abundant in K+ since secretion of K+ is flow dependent: can lead to hypokalemia (would increase pH) most of these lead to decreased bicarb & increased Cl-: normal anion gap |
