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58 Cards in this Set
- Front
- Back
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Where do we know that most of the body's K is?
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INTRAcellular
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So what will a shift of K+ out of cells cause?
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Hyperkalemia
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And what will a shift of K into cells cause?
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Hypokalemia
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What are 3 things that happen to K at the nephron?
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-Filtered
-Secreted -Reabsorbed |
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What maintains K balance in the body?
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Urinary excretion exactly equivalent to dietary intake
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What are 3 determinants of K excretion and balance?
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-Dietary intake
-Aldosterone -Acid-base status |
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What is a major difference in renal handling of potassium compared to sodium?
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Sodium is always reabsorbed almost completely - Potassium reabsorption varies WIDELY
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What is the TF/P ratio of K in bowman's capsule?
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1 - it's filtered freely
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What happens to K in the PCT?
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67% of it is reabsorbed (like Na)
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What happens to K in the TAL of the LOH?
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20% of filtered K is reabsorbed
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What transporter reabsorbs K in the TAL?
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Na/K/2Cl
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What happens to K at the distal tubule and collecting duct?
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EITHER reabsorption OR secretion! Depending on Dietary intake.
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What is the mechanism for K reabsorption at the intercalated cells?
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A lumenal H/K ATPase
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When is the ONLY time that these cells reabsorb K?
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When dietary K is low
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What cells secrete K in the distal tubule/CD?
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OBviously the principal cells under influence of aldosterone
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What DETERMINES the secretion of K at the principal cells?
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Factors that increase the intracellular K conc by Na/K pumping, or decrease K inside the lumen (pull it out)
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How does dietary K affect its secretion by the principal cells?
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Intuitively.. it will push more K into cells, thus higher gradient to flow to the lumen. Low dietary K will reduce secretion.
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How does Aldosterone affect K secretion?
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Aldosterone increases K secretion.
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What is the mechanism of Aldosterone increasing K secretion by principle cells?
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Increases expression/activity of Na/K ATPase so more K is pumped INTO the cells; thus higher gradient for secretion.
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In addition to increasing Na/K ATPase activity how does Aldo increase K secretion?
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Increases expression of Epithelial K channels at the lumenal membrane.
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So what will HYPERaldosteronism (cushings) do to serum and urine K?
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-Hypokalemia
-Hyperkaluria |
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And Addison's/Hypoaldosteronism will do what to serum/urine K?
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-Hyperkalemia
-Hypokaluria |
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How does H+ affect Potassium levels in cells?
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They exchange for each other - at the basolateral membrane of principal cells.
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How will K+ secretion be changed in acidosis?
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H+ will displace K+ from the cells; thus DECREASE K secretion!
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So what will serum levels of K be in
-Acidosis -Alkalosis |
Acidosis = Hyperkalemia (H displaces K in principle cells)
Alkalosis = Hypokalemia (More K in cells, more secretion/loss) |
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How do Thiazide and Loop diuretics affect K secretion?
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They INCREASE it - more Na delivery to the distal tubule/CD increases Na/K exchange so more K inside cells gets excreted!
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So what can Thiazide/Loop diuretics cause?
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Hypokalemia
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What do K+ SPARING diuretics cause if used ALONE?
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Hyperkalemia
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How does Spironolactone spare K secretion?
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By antagonizing Aldosterone so lowers activity of Na/K ATPase
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Where do Triamterene and Amiloride act?
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Directly on the principal cells
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What is the most IMPORTANT use of the K-sparing drugs?
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In combo with Thiazides/Loops to offset their effects of causing hypokalemia.
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What will excess anions like HCO3 do to K secretion? How?
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INCREASE K secretion - by making the lumen more neg, it pulls K into the lumen
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Where is Urea reabsorbed in the nephron?
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50% at the PCT, passively
50% at the medullary CD |
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What controls the reabspn of Urea at the medullary CD? Why?
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ADH - it regulates urea recycling which helps control the inner medulla osmotic gradient
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Where is the majority of PHOSPHATE reabsored, and how?
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85% at PCT - by Na/Phosphate cotransport
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How much filtered Phosphate is thus excreted typically?
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15%
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What hormone regulates PO4 excretion and how?
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PTH - inhibits reabsorption in the PCT
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What is the MECHANISM of PTH inhibiting Phosphate reabsorption?
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1. Activates adenylyl cyclase
2. Increases cAMP 3. Inhibits Na/PO4 cotransport |
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So what does PTH do to urine?
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-Increases Phosphate
-Increases cAMP |
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What does Phosphate do in urine? So what do we call it?
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Acts as a buffer for H+ - Titrateable acid
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How much plasma Calcium is filtered at the glomerulus?
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Only 60%!
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At what nephron segments is the majority, 90% of calcium reabsorbed and how?
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PTC and TAL - passively by coupling to Na reabsorption
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What diuretics will INCREASE calcium excretion by inhibiting reabsorption?
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Loop diuretics - by inhibiting Na reabsorption, they hence inhibit Ca reabsorption
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What must be done if loop diuretics are used for the purpose of excreting more calcium in hypercalcemia?
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Replace volume!
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Where is the other 8% of Calcium reabsorbed? How?
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Distal tubule and CD - by ACTIVE reabsorption
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What regulates this ACTIVE reabsorption of calcium?
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PTH!
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How does PTH increase Ca reabsorption? (mechanism)
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By activating Adenylyl cyclase and increasing cAMP.
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What else can increase Ca reabsorption by active transport at the distal tubule/CD?
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THIAZIDES - thus treat idiopathic hypercalciuria
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Where is Magnesium reabsorbed?
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-PCT
-TAL -Distal tubule |
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How do Mg and Ca interact at the TAL?
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They compete for reabsorption; so Hypercalcemia will INCREASE Mg EXCRETION and vice versa.
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What are 7 things that cause HyperKALEMIA due to shifting K out of cells?
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HIBACED
-Hyperosmolarity -Insulin deficiency -B-blockers -Acidosis -Cell lysis -Exercise -Digoxin |
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Why does Hyperosmolarity cause hyperkalemia?
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Because Water goes where the solutes are, so K goes with it
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Why does Insulin deficiency cause hyperkalemia?
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Because Insulin packs away K into cells just like it does glucose
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Why does Acidosis cause HyperKalemia?
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Because H+ displaces K+ inside cells and pushes them out into plasma.
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Why does Digoxin cause Hyperkalemia?
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Inhibits Na/K ATPase so less is pumped from serum into cells.
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What are 4 causes of HypOkalemia?
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HIBA
-Hypoosmolarity -Insulin -B-AGonists -Alkalosis |
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What are 6 things that will increase Distal tubule/CD secretion of potassium?
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HHALLT
-High K diet -Hyperaldosteronism -Alkalosis -Lumenal anions -Loop diuretics -Thiazide diuretics |
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What are 4 things that will DECREASE distal tubule/CD secretion of K?
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HALK
-Hypoaldosteronism -Acidosis -Low K diet -K-sparing diuretics |
