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16 Cards in this Set
- Front
- Back
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What is normal plasma calcium?
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2.5mmol/L
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How much calcium is biologically active? how much is bound to proteins?
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50% is Ca2+= biologically active
40% is bound to plasma proteins |
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How does the kidney generally process calcium?
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it is filtered and reabsorbed.
NOTE: that only 60% of total calcium is available for filtration. So filtered load (GFR*Pca) needs to be modified to GFR*Pca*.6 to represent that only 60% is able to cross into the kidney |
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Where does reabsorption of Ca2+ occur in the kidney?
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everywhere in the nephron EXCEPT the descending loop of henle (which isnt permeable to ions, only water)
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Where does most Ca2+ reabsorption occur?
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in the proximal tubule 67%
also thick ascending limb 25% |
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How does Ca2+ reabsorption occur in the proximal tubule?
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this is passive reabsorption, coupled to Na+
so anything that changes proximal tubule Na+ affect Ca2+ (paracellular) |
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How does Ca2+ reabsorption occur in the thick ascending limb of Loop of Henle?
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The lumen positive potential drives Ca2+ OUT of the tubular fluid and into the cell.
The slight lumen positive charge is caused by K+ |
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What interferes with Ca2+ reabsorption in the thick ascending limb?
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this is caused by loop diuretics, which inhibit the Na+,2Cl-,K+ symport.
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How does calcium reabsorption occur in the distal tubule?
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it diffuses along Ca+2 channels on the lumenal surface
it can be actively transported out of the cell into the interstitum by Ca2+ ATPase or Na+-Ca2+ exhange |
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What stimulates ca2+ uptake in the distal tubule?
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PTH (which increases blood calcium)
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How do thiazides affect Ca2+? where?
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these increase Ca2+ reaborption in the distal tubule of the nephron.
cause by blocking NaCl from the lumenal side, so the Na/Ca exchange on the basal side pumps IN more Na, and more Ca OUT of the cell into the blood. this creates a draw for Ca2+ from the lumenal side |
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How much phosphate is filtered?
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about 90%, the rest is bound to protein
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How much phosphate is excreted? what is its role?
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15% is excreted, this is the most important buffer anion
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How does phosphate reabsorption occur in the proximal tubule?
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Cotransport with Na, 3Na+- 1 Po4 3- symport.
Na+ reabsoprtion affects PO4 reabsoprtion |
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How does PTH affect phosphate?
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this inhibits the Na/PO4 cotrasporter in proximal tubule, and decreases the Tm for phosphate
aka promotes PO4 excretion |
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Where is the major site of reabsorption of magnesium in the kidney?
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this is done in the thick ascneding limb (much like Ca2+)
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