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19 Cards in this Set
- Front
- Back
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What's the difference between the tight junctions in the SI and LI?
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SI - leaky low resistance tight junctions that allow paracellular movement
LI - tight high resistance tight junctions which do not permit paracellular movement |
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What goes on in the jejunum as far as absorption is concerned?
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Na. It's Na land. It's the same as the early proximal tubule
1. Na is cotransported with sugar or AA or Na/H exchange 2. Na gets out of the basolateral side per Na-K ATPase NOTE: the H on the apical surface comes from a CO2+H2O rxn that produces H2CO3 per carbonic anhydrase and then H + HCO3. the bicarb goes into the blood, the H goes into the intestinal lumen |
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How does the jejunum and ileum differ as far as absorption goes?
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1. on the apical surface there is an additional Cl/HCO3 exchanger that pulls Cl into the cell
2. the same CO2+H20 rxn is going down, but the bicarb goes into the lumen to get Cl into the cell and then into the body |
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How does absorption work in the colon?
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just like the late distal tubule and collecting ducts
1. apical surface has Na channels that are upregulated by aldosterone. Na comes in 2. this causes K to move out into the lumen 3. on the basolateral surface there is a Na/K ATPase to get Na into the body and K into the cell 4. K also leaves the cell and goes back into circulation diarrhea causes high flow. high flow causes /\ K loss. this can lead to hypokalemia. |
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Where does fluid and electrolyte secretion mainly take place?
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the epithelial cells of the intestinal crypts
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Tell me about Cl secretion in the colon. Do it.
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recall this is going down in the crypts
1. Cl channels are on the apical membrane and will open (indirectly) in response to basolateral stimulation by Ach, VIP 2. adenylyl cyclase is activated and generates cAMP 3. cAMP opens the Cl channels and allows Cl secretion 4. Na and water follow Cl into the lumen |
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What's the deal with cholera?
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Cholera toxin move into the cell and causes /\ adenylyl cyclase activity => /\ cAMP => secretory diarrhea since Easters.
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How is Ca absorbed?
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absorption is in the small bowel
1. vit D3 is inactive and is in the diet 2. in the liver D3 => 25-hydroxycholecalciferol (inactive) 3. proximal kidneys convert to 1,25-dihydroxycholecalciferol (active) by 1alpha-hydroxylase 4. active vit D inducses synthesis of calbindin D-28 K (vit D-dependent Ca-binding protein) |
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How is Fe absorbed?
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Fe2+ or heme iron is absorbed across the apical membrane, digested by lysosomal enzymes to make just free iron, free iron binds to apoferritin to move across the basolateral membrane and into the blood.
in the blood iron bound to beta-globulin is called transferrin and moves to the liver to be stored or shipped off to the bone marrow to make hemoglobin. |
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Where does most water absorption occur?
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jejunum and a little in the ileum
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How do glucocorticoids regulate secretion/absorption?
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/\ net absorption in SI and LI by /\ Na/K ATPase on basolateral surface
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How does epi regulate secretion/absorption?
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/\ net absorption in the ileum by alpha receptors on epithelium to \/ secretion and inhibit secretomotor activity at submucosal ganglia
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How does somatostatin regulate secretion/absorption?
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/\ water and salt absoprtion at ileum and colon and inhibits secretion by \/ cAMP levels and \/ secretomotor activity on eteric neurons
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How do opiods regulate secretion/absorption?
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/\ absorption of salts and water in intestine by delta-receptors to inhibit motility.
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What neural components regulate absorption and secretion?
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1. submucosal ganglia => /\ secretomotor neurons => /\ secretion by Ach or VIP action
2. presence of glucose, \/ pH, bile, salt, ethanol, cholera, antigen causes ENS reflexes |
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What's the deal with Crohn's and IBD?
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any dz process that decreases SA will cause a \/ absorption. you're looking at malnutrition and dehydration.
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What's the deal with idiopathic hemochromatosis?
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this is iron overload and deposition in the liver, skin. you'll have bronzing. ferritin is saturated and hemosiderin is deposited in multiple tissues.
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What's the deal with Rickets?
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The predominant cause is a vitamin D deficiency, but lack of adequate calcium in the diet may also lead to rickets (cases of severe diarrhea and vomiting may be the cause of the deficiency).
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What's the deal with CF and GI absorption/secretion?
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in CF, the cholride channel on the apical side of the intestinal epithelial cell is defective.
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