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26 Cards in this Set

  • Front
  • Back
Renal K+ excretion is increased by 5 factors
1) Increased K+ intake
2) Mineralcorticoids (aldosterone)
3) Alkalosis (low H+)
4) Increased excretion of anions
5) Increased Na+ excretion
K+ secretion pathways for high dietary conditions
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
Why aldosterone action is not 100% K+ clearing
- 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.
Why Na+ depletion does not necessarily lead to K+ excretion - 2 pathways...
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!
Distal tubular flow rate effect on K+ secretion
- 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
Furosemide purpose and mechanism
- Loop diuretic for CHF and edema
- Inhibits Na+ reabsorption in thick ascending limb
- Leads to excess K+ secretion also - by flow mechanism!
Fixed acids vs. volatile acids
- 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.
Henderson-Hasselbach equation
- Calculates pH
pH = Pka + log([A-]/[HA])
*** Main point = RATIO of dissociation is key, not absolute values
Isohydric principle
- All buffers in concert together
- Overall pH change from any single buffer system
3 elements of tiered pH balance system
1) Buffer systems
2) Respiratory control
3) Renal control
Main buffer system
- HCO3- system!
- PKa = ~6.1
- Technically set up to eq. outside physiological pH...
- Useful because respiration/secretion of CO2/HCO3 can easily regulate system
2 HCO3 buffer system advantages
1) Components present in large amounts
- Can breathe in a crapload of CO2...
2) Open system - amounts easily adjusted by respiratory/renal systems
Renal regulation vs. respiratory key difference
- 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
Primary renal pH correction mechanism
- Excrete excess NH4 or H+
- Return HCO3 to circulation
HCO3 reclamation mechanism
- 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
Link between Na+ and HCO3- reabsorption
- H+/Na+ antiporters drive HCO3 reclamation and Na+ reabsorption
- Na+ reabsorbtion -> H+ secretion
Inhibition of carbonic anhydrase or Na+ reabsorbtion on eachother
- Inhibited Na+ reabsorption will decrease HCO3- reclamation
- Inhibited HCO3- reclamation can negatively impact Na+ reabsorption
New HCO3- generation
- H2O + CO2 -> H2CO3 -> HCO3- + H+
- H+ is complexed with HPO42-·2Na+
- Get H2PO4-·Na+
- Actual completely NEW HCO3!
Ammoniagenesis
- 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-
2 Ammoniagenesis regulating factors
- pH and PCO2
Ammoniagenesis regulation flexibility
- Very flexible - can literally be turned completely off!
4 basic acid-base disorders
- Respiratory acidosis/alkalosis and metabolic acidosis/alkalosis
Respiratory acidosis cause/compensation
- Hypoventilation
- Kidneys increase H+ excretion to increase plasma [HCO3]
Respiratory alkalosis cause/compensation
- Hyperventilation
- Kidneys increase HCO3 excretion, decrease plasma [HCO3]
Metabolic acidosis cause/compensation
- Decreased HCO3 in plasma for some reason
- Hyperventilation
- Kidneys try to increase H+ excretion
Metabolic alkalosis cause/compensation
- Increased HCO3 in plasma for some reason
- Hypoventilation
- Kidneys try to increse HCO3 excretion