Absorption Of Ions

cgeorge's version from 2016-01-26 17:38


Question Answer
Stem/Progenitor cells are Essential for crypt
Paneth cell are important forHost defence against microbes
Stem cells are found in the ... in the SICrypt
Villous enterocyte roleAbsorption
Crypt enterocyte roleSecretion
Increase SA by 3 adaptions1) Folds of Kerckring. 2) Villi 3) Microvilli
How many L of chyme go through SI from stomach8.5L
How much chyme is reabsorbed in SI6.5L
Prostprandial state refers to When you have just eaten
Transcellular movement isSolute must cross 2 cell membranes (apical and basal). Active transport involved
Paracellular movement isSolute moves passively between adjacent epithelial cells via tight junctions
Describe mechanism of absorpin waterTransport Na,Cl & HCO3 into intercellular spaces - Hypertonic. Water moves from lumen via osmosis
Where is Na absorbed Jejunum, Ileum and colon
Where is K absorbedJejunum, Ileum
Where is K net secretedColon
Where is Cl absorbedJejenum, ileum, colon
Where is HCO3 absorbedJejunum
Where is HCO3 secretedIleum,colon
Describe mechanismg using SGLT1Na/K pump on basal membrane secretes Na out. Na comes in via SGLT1 with glucose. Mechanism inhibited by cAMP
Desrcibe mechanism using Na/H exchangerFor every Na in, 1 H out
Describe Na/H and Cl/HCO3 exchanger (Electroneutral) Na/K exchanger coupled with Cl/HCO3 exchanger. Mechanism occurs in fasted state. Inhibited by camp/cgmp/calcium. Chloride in, HCO3 out. Na in, H+ out
What are the effects of enterotoxinsCause diarrhoea by increasing cAMP levels and inhibiting NaCl absorption
Describe effect of mineralcorticoids on Na absorptionIncrease Na absorption via 1) Increase opening of apical Na channels 2) Insert Na channels into apical membrane 3) Increase synthesis of apical Na channels and Na/K pumps
3 mechanisms of Cl absorption1) Passive Cl absorption 2) Parallel Na/H and Cl/HCO3 exchange 3) Cl/HCO3 exchange
What is congenital chloridorrheaAutosomal recessive disorder. Absence of apical Cl/HCO3 exchanger. Causes diarrhoea high in [Cl] due to absence of apical membrane Cl/HCO3 exchanger. Because secretion of HCO3 is reduced, patients have alkaline blood
Treatment of congenital chloridorrheaPPI inhibitors
Absorptagogues promoteAbsorption
Secretagogues promoteSecretion-Diarrhoea
Aldosterone (Absorptagogue) works byStimualte Na absorption via epithelial Na channels> Increased water absorption
Angiotensin (Absorptagogue) works byUpregulating apical membrane Na/H exchanger, again stimulating water absorption
4 categories of secretagogues are1) Bacterial enterotoxins 2) Hormones and neurotransmitters 3) Products of cells of the immune system 4) Laxatives
Effect of secretagogueInhibit Na absorption, induce Cl secretion by elevatig levels of Camp/Ca
Cholera caused by the bacteriumVibrio chloerae which releases cholera toxin (an enterotoxin)
Treatment strategy for choeleraLoperamides which supress myenteric plexus. Decrease smooth muscle motility, increasing amout of time there is to absorb water. Decrease diarrhoea
How much calcium does SI absorb per day500mg/day.
How much calcium does SI secrerte per day325mg/day
Passive transport of calcium occursThroughout the small intestine via the paracellular pathway. Not under controll of vitamin D
Active transport of calcium occursOnly in the epithelal cells of the duodenum and is under control of vitamin D
3 steps of active Ca absorption1) Uptake of ca via Ca channels. 2) Cytosolic Ca binds to calbindin inside cell 3) Ca pump and Na/Ca exchanger on basolateral membrane extrudes Ca from cell
Active form of vitamin D is1,25-dihydroxy-vitamin D