True or False?
Potassium secretion will occur in the distal tubule and collecting ducts of the nephron with or without aldosterone.
Aldosterone just makes the process more efficient.
What is the result as Na+ is reabsorbed in the DT and collecting ducts, given the fact that no Cl- channels or transports exist here?
The outside of the cell membrane becomes more negative, while the cytoplasm becomes more positive.
What causes potassium to move out of the tubular epithelial cells of the DT and collecting ducts?
It is repelled by the intracellular positive charge and attracted to the extracellular negative charge. It also moves down its concentration gradient (caused by the Na+/K+ ATPase on the basolateral membrane of the cell).
True or False?
The exchange that occurs in the DT and collecting duct of the nephron involving Na+ and K+ is a coupled symport process.
It is a loose exchange between the two solutes, but they experience independent permeabilities.
What two triggers initiate aldosterone secretion?
1.) Angiotensin II
What allows for the secretion of potassium in the absence of aldosterone?
1.) Na+/K+ ATPase on the basolateral membrane of tubular epithelial cells
2.) Concentration gradient of K+ from interstitium to tubular cell
*In short, K+ can stimulate its own secretion by bulk flow/balance.
In the absence of aldosterone, which solute - sodium or potassium - can cause a more significant change in plasma concentration of that solute.
Since potassium can somewhat regulate its own secretion by bulk flow.
An increase in sodium delivery to the DT will cause a(n) (increase / decrease) in the amount of potassium secretion.
K+ must be secreted in order to maintain an electrochemical gradient.
What might cause an increased delivery of sodium to the DT of the nephron?
High blood pressure, causing pressure diuresis and thus less proximal reabsorption.
Why doesn't increased MAP lead to hypokalemia?
Although increased BP can cause increased K+ secretion in response to increased Na+ reabsorption in the latter nephron, Aldosterone secretion shuts down in response to higher MAP in order to avoid hypokalemic conditions.