Term
| Approximately what percent of the potassium excretion occurs in the urine? Where is the rest excreted from? |
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Definition
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Term
| Approximately what percent of the potassium is located in the extracellular fluid? What is the typical extracellular concentration? |
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Definition
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Term
| How is a rapid rise in extraceullular K following a meal prevented? |
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Definition
1) rapid uptake via Na/K ATPase
2) inc. intracellular K causes insulin release
3) insulin causes K uptake
4) extracellular K causes aldosterone release |
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Term
| What is the equation used to determine the total filtered K+? |
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Definition
| 1) Total Filtered K = GFR * serum potassium concentration |
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Term
| Approximately what percent of filtered K is reabsorbed in the PCT? How? thick ascending limb of loop of henle? How? DCT and Collecting tubule? How? |
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Definition
1) 67%; paracellularly via solvent drag and luminal positive potential difference via Cl
2) 20%; Na/K/2Cl-cotransporter
3) 10%; principal cells |
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Term
| Where does K secretion in the collecting tubules occur? How do these cells accomplish this? How does reabsorption occur? |
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Definition
1) principal cells; K channels w/ high Na+ w/ aldosterone
2) intercalated cells; via H/K ATPase |
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Term
| What are the three most important factors affecting K secretion by principal cells in the CD? What are some other factors? |
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Definition
1) aldosterone - leads to both K and Na channels, inc. Na/K ATPase
2) delivery of sodium to distal nephron - movement across membrane facilitates K movement into tubular fluid via membrane potential
3) plasma postassium concentration - stimulates activity of Na/K ATPase and the driving force
4) tubular flow rate; diuretics (K-sparring/-wasting) |
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Term
| Why are loop and thiazide diuretics potassium wasting diuretics and amiloride K-sparring? |
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Definition
1) loop and thiazide activate aldosterone and increased Na to collecting duct -> both of which increase K secretion
2) amiloride inhibits Na channels in principal cells, decreasing K driving force. |
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Term
| What are major hormones that influence internal distribution of potassium? What is major net effect? |
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Definition
1) insulin (uptake)
2) epi (muscle, liver uptake)
3) Glucagon (liver release)
4) growth hormone (uptake)
5) aldosterone (slightly inc. uptake) |
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Term
| What are major factors that affect the internal distribution of potassium? |
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Definition
1) hormones
2) acid-base status
3) drugs
4) hypertonicity
5) exercise
6) rapid cell destruction
7) periodic paralysis (rare) |
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Term
| What is the effect of acidosis on potassium storage? Which is greater: metabolic vs respiratory disturbances; acidosis vs. alkalosis? bicarbonate vs. pH? |
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Definition
1) movement out of cells
2) metabolic > respiratory; acidosis > alkalosis; bicarbonate >> pH |
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Term
| What is the effect of hypertonicity on potassium cellular storage? |
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Definition
| 1) potassium drag extracellularly and plasma levels increased |
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Term
| What is the effect of exercise on potassium storage in the cells? |
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Definition
| 1) releases potassium from cells |
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Term
| What are examples of drugs that increase potassium release from cells? increase uptake? |
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Definition
1) digitalis, succinyl choline, beta blockers, alpha agonists
2) beta agonists, insulin, alpha antagonists |
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Term
What are physiologic consequences of hypokalemia on the following:
cardiac system? |
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Definition
1) ST depression
2) lowered T wave voltage
3) increased U wave voltage
4) increased automaticity of cardiac muscle |
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Term
What are physiologic consequences of hypokalemia on the following:
skeletal muscle?
smooth muscle?
CNS?
Kidney?
Glucose tolerance? |
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Definition
1) weakness - limbs first, respiratory muscles later; decreased tendon reflexes; rhabdomyolysis
2) paralytic ileus and gastric dilation
3) confusional states; affective disorders
4) impaired kidney concentrating ability (unresponsive to ADH/volume depletion)
5) glucose intolerance |
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Term
| What are the four general causes of hypokalemia? |
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Definition
1) decreased intake (unusual)
2) increased kidney excretion (DKA, diuretics, RTA, Cushings)
3) non-kidney losses (gastric losses, diarrhea, profuse sweating)
4) transcellular shifts (hypokalemic periodic paralysis, insulin admin, catecholamine secretion) |
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Term
| What are the major treatments for hypokalemia? |
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Definition
1) cautious replacement
2) tx of underlying cause
3) IV replacement should be monitored |
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Term
What are the physiologic consequences of hyperkalemia for the following systems:
cardiac
muscular |
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Definition
1) peaked T waves; widened QRS, lengthening of PR, disappearance of P wave, ventricular standstill
2) muscle weakness |
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Term
| What are the general causes of hyperkalemia? |
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Definition
1) decreased excretory capacity (acute kidney injury, chronic kidney disease, RAAS blockade, Addison's disease)
2) increased intake (usu w/ Pts w/ dec excretory capcacity; potassium supplements; dietary indiscretion)
3) transcellular shifts (acid-base disturbances, exercise, insulin deficiency, tumor lysis syndrome) |
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Term
| What are the major Tx options for hyperkalemia? |
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Definition
1) reversal of membrane effects (calcium)
2) transfer of K into cells (bicarb w/ volume, insulin w/ glucose, Beta2 agonist)
3) removal of K from body (exchange resins, dialysis) |
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