Term
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Definition
NAE=Titratable acid secretion (40%) + NH3 (60%) - HCO3 reabsorption
Changes in acid excretion done through ammoniagenesis. |
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Term
| Generalized HCO3 absorption scheme |
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Definition
1. HCO3- is broken down by apical CAIV into OH- and CO2.
2. OH- combines with a proton to form water, and both CO2 and water diffuse into the cell.
3. CAII inside the cell converts CO2 and H20 into H2CO3, which then gives up a proton.
4. H+ is transported into the tubule lumen through Na, H transporters or H+ ATPases where it recombines with OH-.
5. HCO3- is transported basolaterally into the interstitum through Na, HCO3 transporters or Cl, HCO3 transporters.
THERE IS ALWAYS A 1:1 RATIO OF H+ SECRETION TO HCO3- REABSORPTION!!!! |
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Term
| Formation of titratable acid |
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Definition
| Secreted H+ joins with HPO4 in tubule lumen and is excreted as H2PO4. |
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Term
| Diffusion mechanism of NH3 |
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Definition
1. NH4 inside cell gives up a proton to become uncharged NH3. (non ionic diffusion)
2. NH3 and H+ go to tubule lumen and rejoin to form NH4+. Charged nature revents it from diffusing back into cell (ion/pH trapping). |
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Term
| Reabsorption of HCO3- in kidney |
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Definition
| 80% reabsorbed in the proximal convoluted tubule. 10% reabsorbed in thick ascending limb. 6% reabsorbed in the distal convoluted tubule. 4% reabsorbed in the collecting duct. |
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Term
| HCO3- reabsorption in the early PCT |
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Definition
| HCO3- is broken down to OH- (combines with secreted H+) and CO2 by CAIV on the lumen side of the cell membrane. CO2 diffuses into the cell and combines with water to form H2CO3 using CAII. Carbonic acid then breaks down to bicarbonate and H+. Bicarbonate is then reabsorbed basolaterally using a Na, bicarbonate exchanger. H+ ion secreted into the lumen using Na, H antiporter (major) and H+ ATPase (minor), which then recombines with OH- to form water. |
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Term
| HCO3- reabsorption in the late PCT |
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Definition
Same as the early proximal tubule except:
1. No more CAIV on apical surface.
2. Addition of Cl, HCO3 antiporter on basolateral side. |
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Term
| HCO3- reabsorption in the TAL |
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Definition
Same as the early proximal tubule except:
1. No more CAIV on apical surface.
2. Na, HCO3- transporter replaced by Cl, HCO3- antiporter. |
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Term
| HCO3- reabsorption in the alpha intercalated cells and collecting duct cells. |
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Definition
Same as the early proximal tubule except:
1. No more CAIV on apical surface.
2. Na, HCO3- transporter replaced by Cl, HCO3- antiporter.
3. H ATPase is the primary proton secreter into the lumen.
4. Addition of H, K antiporters. |
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Term
| Aldosterone effects of H+ secretion |
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Definition
1. Stimulates H+ ATPase
2. Stimulates Na reabsorption through Na channels in the collecting tubule, which generates a negative charge in the lumen (favors H+ and K+ secretion). |
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Term
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Definition
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Term
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Definition
1. Glutamine enters the proximal tubule.
2. Glutaminase converts glutamine into NH4+ and glutamate.
3. Glutamate is then converted into NH4+ and alpha ketoglutarate (metabolized into two HCO3-) through glutamate dehydrogenase. |
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Term
| NH4+ diffusion in kidneys |
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Definition
1. In the thick ascending limb, NH4+ enters cell through K channels and Na, K, Cl cotransporter.
2. Diffuses out basolaterally into medullary interstitum.
3. This creates a concentration gradient that allows NH4+ to diffuse through thin descending limb cells and medullary collecting duct cells (also enter through Na, K ATPase) into the tubule lumen.
Some NH4 also escapes medullary interstitum to travel to the liver. |
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Term
| Potassium effects on H+ secretion |
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Definition
| Higher potassium concentrations result in decreased H+ secretion. |
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Term
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Definition
| CA inhibitor, inhibits H+ secretion |
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Term
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Definition
| Aldosterone antagonist, lowers H+ secretion. |
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