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26 Cards in this Set
- Front
- Back
Renal K+ excretion is increased by 5 factors
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1) Increased K+ intake
2) Mineralcorticoids (aldosterone) 3) Alkalosis (low H+) 4) Increased excretion of anions 5) Increased Na+ excretion |
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K+ secretion pathways for high dietary conditions
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1) More K+ uptake, excretion by collecting duct cells
2) High [K+] -> Aldosterone secretion by adrenal (sensitive to electrical gradient) - Higher plasma aldosterone -> higher Na/K ATPase activity in collecting duct principal cells |
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Why aldosterone action is not 100% K+ clearing
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- Aldosterone activates Na/K ATPase which puts K+ into tubule lumen
- However, K+ can leak back between tight junctions to interstitium and re-enter principal cells, etc. |
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Why Na+ depletion does not necessarily lead to K+ excretion - 2 pathways...
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1) Low Na+ -> aldosterone secretion -> higher plasma aldosterone -> K+ secretion
2) Low Na+ -> low GFR -> higher Na+ reabsorption -> less fluid to cortical collecting ducts -> less chance for K+ secretion *** 2 forces can actually cancel eachother out! |
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Distal tubular flow rate effect on K+ secretion
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- K+ secretion increases with flow rate!
- K+ diffuses across principal cell membrane to tubule lumen - Slow flow rate = K+ gradient diminishes -> less K+ diffusion - Higher flow rate = K+ gradient maintained -> more overall K+ diffusion |
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Furosemide purpose and mechanism
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- Loop diuretic for CHF and edema
- Inhibits Na+ reabsorption in thick ascending limb - Leads to excess K+ secretion also - by flow mechanism! |
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Fixed acids vs. volatile acids
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- Volatile acids = produced by CO2 + H2O -> HCO3- + H+
- These are volatile because they tend to be blown off through the lungs - Normally, little to do with the kidney - Fixed acids = usually from metabolic processes - Sulfuric acid, phosphoric acid, lactic acid, etc. |
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Henderson-Hasselbach equation
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- Calculates pH
pH = Pka + log([A-]/[HA]) *** Main point = RATIO of dissociation is key, not absolute values |
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Isohydric principle
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- All buffers in concert together
- Overall pH change from any single buffer system |
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3 elements of tiered pH balance system
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1) Buffer systems
2) Respiratory control 3) Renal control |
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Main buffer system
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- HCO3- system!
- PKa = ~6.1 - Technically set up to eq. outside physiological pH... - Useful because respiration/secretion of CO2/HCO3 can easily regulate system |
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2 HCO3 buffer system advantages
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1) Components present in large amounts
- Can breathe in a crapload of CO2... 2) Open system - amounts easily adjusted by respiratory/renal systems |
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Renal regulation vs. respiratory key difference
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- Respiratory pH correction is fast, but can't truly correct acidosis
- Simply compensates to fix pH at expense of hyper/hypoventilation - Actual [HCO3-] is still bad... - Renal slowly but completely fixes the pH problems |
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Primary renal pH correction mechanism
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- Excrete excess NH4 or H+
- Return HCO3 to circulation |
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HCO3 reclamation mechanism
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- HCO3- in tubules converted to OH- and CO2 (via lumenal carbonic anhydrase)
- CO2 enters cell, combines with OH- again -> HCO3- -> reclaimed! - OH- in lumen combines with H+ coming from inside of cell -> H2O - This H2O can move inside cell also -> OH- and H+ - This is the OH- that recombines with CO2 *** Overall, consume 1 HCO3 to reclaim 1 HCO3 |
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Link between Na+ and HCO3- reabsorption
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- H+/Na+ antiporters drive HCO3 reclamation and Na+ reabsorption
- Na+ reabsorbtion -> H+ secretion |
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Inhibition of carbonic anhydrase or Na+ reabsorbtion on eachother
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- Inhibited Na+ reabsorption will decrease HCO3- reclamation
- Inhibited HCO3- reclamation can negatively impact Na+ reabsorption |
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New HCO3- generation
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- H2O + CO2 -> H2CO3 -> HCO3- + H+
- H+ is complexed with HPO42-·2Na+ - Get H2PO4-·Na+ - Actual completely NEW HCO3! |
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Ammoniagenesis
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- 2nd way to generate new HCO3-
- Glutamine -> NH4+ + α-ketoglutarate - NH4+ -> NH3 + H+ *** Bottom line = H+ taken up by NH3 -> NH4, excreted - Net gain of HCO3- |
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2 Ammoniagenesis regulating factors
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- pH and PCO2
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Ammoniagenesis regulation flexibility
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- Very flexible - can literally be turned completely off!
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4 basic acid-base disorders
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- Respiratory acidosis/alkalosis and metabolic acidosis/alkalosis
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Respiratory acidosis cause/compensation
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- Hypoventilation
- Kidneys increase H+ excretion to increase plasma [HCO3] |
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Respiratory alkalosis cause/compensation
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- Hyperventilation
- Kidneys increase HCO3 excretion, decrease plasma [HCO3] |
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Metabolic acidosis cause/compensation
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- Decreased HCO3 in plasma for some reason
- Hyperventilation - Kidneys try to increase H+ excretion |
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Metabolic alkalosis cause/compensation
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- Increased HCO3 in plasma for some reason
- Hypoventilation - Kidneys try to increse HCO3 excretion |