Flashcards in Renal Chapter 8: Renal Regulation of Potassium Balance Deck (40)
Will a patient suffering from alkalosis (vomitting) manifest increased or decreased urinary excretion of potassium?
increased urinary excretion of potassium solely as a result of the alkalosis and will, therefore, become potassium deficient
Control of potassium excretion is achieved mainly by regulating the rate of which
of the following?
A. Potassium filtration
B. Potassium reabsorption
C. Potassium secretion
The answer is C: potassium secretion.
When on a high-potassium or high-sodium diet, is it possible to excrete more potassium
or more sodium in the urine than is filtered?
For potassium, yes. High rates of secretion may exceed reabsorption.
For sodium, no.
Indicate whether each statement is true or false.
A. In the proximal tubule, the major pathway of reabsorption for both sodium
and potassium is paracellular.
B. In the thick ascending limb, the major pathway of reabsorption for both sodium
and potassium is via the Na-K-2Cl multiporter.
C. In the thick ascending limb, equal amounts of sodium and potassium are
A. False: Most potassium reabsorption is paracellular, but all sodium
reabsorption is transcellular. B. True. C. False: Even though the multiporter
moves equal amounts of sodium and potassium, most of the
potassium leaks back and is recycled.
The presence of high amounts of nonreabsorbed solute (eg, glucose) in the proximal
tubule inhibits proximal tubule potassium reabsorption. True or false?
The answer is true. The excess solute retains water, thus diluting tubular
potassium and reducing the driving force for reabsorption.
The presence of high amounts of nonreabsorbed solute (eg, glucose) in the collecting
tubule inhibits potassium secretion. True or false?
The answer is false. The high amounts of nonreabsorbed solute increase
the sodium content of the luminal fluid, with water accompanying it.
This dilutes potassium. This stimulates potassium secretion both by the dilution effect and by the high rate of sodium reabsorption.
A patient has a tumor in the adrenal gland that continuously secretes large quantities
of aldosterone (primary hyperaldosteronism). Is the rate of potassium excretion
normal, high, or low?
The answer is high. The increased aldosterone stimulates potassium
secretion and, thereby, excretion. Moreover, once enough sodium has
been retained to increase GFR and to cause partial inhibition of proximal reabsorption, the increased delivery of fluid to the cortical collecting
duct further enhances potassium secretion. There is no potassium escape similar to the sodium escape from aldosterone.
A patient with severe congestive heart failure is secreting large quantities of aldosterone.
Is the rate of potassium excretion normal, high, or low?
The answer is relatively normal. One may have answered “high,” assuming that the increased aldosterone would stimulate potassium secretion,
as in Question 8–6. However, this effect is more than balanced by the fact that the patient has a decrease in flow of fluid into the cortical collecting duct (because of decreased GFR and increased proximal and loop reabsorption). Recall that potassium secretion is impaired when the amount of fluid flowing through the cortical collecting duct is reduced.
This explains why patients with the diseases of secondary hyperaldosteronism
with edema do not lose large quantities of potassium,
whereas those with primary hyperaldosteronism do.
A person on a high-potassium diet is excreting large amounts of potassium. This is
accomplished mainly by what mechanism?
A. Reduced reabsorption in the proximal tubule
B. Reduced reabsorption in the thick ascending limb
C. Reduced reabsorption in the connecting tubule and collecting ducts
D. Increased secretion in the connecting tubule and collecting ducts
The answer is D. There is little control over potassium transport before the connecting tubule. When excretion is high, the major process leading
to high excretion is high secretion by the connecting tubule and cortical collecting duct.