Renal help? confused

Discussion in 'Step I' started by Pisiform, 09.23.14.

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  1. Pisiform

    Pisiform Oh Crap!!! 7+ Year Member

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    So I have couple of things that I am not sure if I have it straight.

    1) So when we are talking about Hypo/hyperkalemia, we are talking about K+ concentration in serum and NOT inside cells. Am I right?

    2) Lasix (loop diuretic) causes Metabolic Alkalosis. It does so by preventing K+ reabsorption (blocks NKCC) so serum K+ decreases. This causes a transcellular shift which causes K+ to leave the cell and go into serum and H+ from serum going into cell. Low serum H+ causes Alkalosis. Am I right?

    3) Hyperkalemia is associated with metabolic acidosis. Same principle. High K+ in serum would go into the cell which would causes H+ in the cell to come out into the serum causing acidosis?

    I just need to know if thats what exactly happening? I get confused by this quite often. Thanks
     
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  3. SBR249

    SBR249 7+ Year Member

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    1) anything that ends with -emia usually refers to things within the blood

    2) Furosemide has a more direct effect. By inhibiting Na+ reabsorption in the loop of Henle, it causes greater distal sodium delivery to the collecting duct. The increased distal delivery will increase sodium reabsorption distally. Because the principle sodium channel in the collecting duct is the epithelial sodium channel (ENaC) which only allows sodium to pass through, there must be counter-ions to balance the reabsorption of sodium. In the collecting duct the counter-ions are potassium and H+ secreted by the intercalated cells. Thus, the loss of H+ in the collecting duct leads to metabolic alkalosis.

    Another contributing factor to metabolic alkalosis is the volume loss caused by furosemide. Remember that the largest amount of water is actually reabsorbed in the proximal tubule which is also the site of HCO3- reabsorption. In response to diuretic induced volume loss, the proximal tubules will work harder to reclaim water and the solvent drag will actually increase the efficiency of reabsorption of most solutes there including HCO3-

    3) Hyperkalemia can cause metabolic acidosis through the actions of the collecting duct as well. The counter-ions for Na+ in the CCD is K+ and H+, if there's hyperkalemia, then proportionally more K+ will be secreted and less H+.

    Also remember that hyperkalemia inhibits production of ammonia by the proximal tubules which is needed as a buffer in the urinary system. The less buffer capacity that urine has, the less H+ that can be secreted which also contributes to acidosis.
     
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