Term
| Why is the kidney important in acid/base regulation? |
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Definition
| Buffering & respiratory systems will stabilize blood pH initially, but to restore long-term homeostasis the kidneys are needed |
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Term
| How do kidneys regulate HCO3- and H+? (3) |
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Definition
-reabsorpton of bicarbonate HCO3-
-regeneration of new bicarbonate with excretion of titratable acid
-excretion of acid as ammonium salts |
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Term
| Where does the majority of bicarbonate reabsorption occur? |
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Definition
| 80% is in the proximal tubule |
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Term
| What enzyme is essential in bicarbonate reabsorption, and what does it do? |
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Definition
carbonic annhydrase
It will either make carbonic acid or break it down, depending on what is required to reach equilibrium withiin the cell |
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Term
| How does bicarbonate move from inside cells of the proximal tubule, to the bloodstream? |
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Definition
| sodium symporters and chloride antiporters |
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Term
| How do hydrogen ions move from inside cells of the proximal tubule, to the lumen? |
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Definition
| sodium antiporters as well as ATPase |
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Term
| How does CO2 and H2O move from the lumen, to within the cells of the proximal tubule? |
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Definition
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Term
| Where does titratable acid excretion occur? |
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Definition
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Term
| What is titratable acid excretion? |
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Definition
| Binding of hydrogen ions with HPO4(2-) or SO4(2-) to produce H2PO4- or HSO4- which is excreted in the urine, coupled with the generation of NEW bicarbonate from the breakdown of H2CO3 to produce said hydrogen ions |
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Term
| Where does acid excretion take place? |
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Definition
distal tubule & collecting ducts
33% is titratable acid excretion
66% is ammonium excretion |
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Term
| What is ammonium excretion? How does it happen? |
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Definition
binding of H+ with toxic NH3 to produce NH4+ which is excreted in the urine.
1. H2CO3 is broken down by carbonic anhydrase in the distal tubule cell.
2. ATPase pumps H+ into the lumen
3. H+ binds with NH3 that was produced from glutamine metabolism to form NH4+
4. NH4+ is excreted in the urine |
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Term
| Where does the NH3 used in ammonium excretion come from? |
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Definition
| metabolism of glutamine in the cortex |
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Term
| How is acidic urine produced? |
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Definition
| intercalated cells of the collecting ducts can insert or remove proton pumps in the plasma membrane, which will pump H+ ions in to the lumen of the collecting duct |
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Term
| Which can be upregulated more quickly, H+ excretion via titrable acid production or ammonium production? |
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Definition
titratable acid
Ammonium production requires increasing the metabolism of glutamine, and it takes a while for the enzymes for this to be activated |
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Term
| What stimulates the excretion of hydrogen ions via urine? |
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Definition
Acidosis
-increased Na/H exchanger activity in PCT
-increased glutamine metabolism = more NH4+ production
-more H+/ATPase activity
Hypokalemia
-high potassium will increase activity of H+/K+ antiporters
Aldosterone
-upregulates H+ ATPase in lumen |
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