Chapter 8 - Renal Regulation of Potassium Balance Flashcards
What are the two cell types in the epithelium of the distal nephron? Which makes up the majority?
Principle cells (majority, 70%), and intercalated cells (subtype A more numerous and subtype B).
The principle cells (secrete/resorb) potassium.
secrete
Type A intercalated cells (secrete/resorb) potassium.
resorb
In the principle cells, how does potassium get from the interstitium to the intracellular space?
Na-K-ATPase
What are the names of the two most important potassium channels in the principle cells (connecting intercellular space to the lumen)
ROMK – renal outer medulla potassium
BK – big potassium
Which potassium channels are utilized under what conditions? (low K, normal K, high K)
Low – neither ROMK nor BK sequestered
Normal – ROMK sequestered, BK off
High – Both ROMK and BK secreting
Type A intercalated cells reabsorb potassium via what pump on the luminal membrane?
H-K-ATPase
List six factors which influence potassium secretion.
Plasma potassium levels – not a dominant factor.
Aldosterone – hyperkalemia stimulates aldosterone secretion (direct action of potassium on the adrenal cortex; does not involve the renin-angiotensin system). Aldosterone increases expression of the Na-K-ATPase pumps and ROMK channels.
Delivery of sodium to the distal nephron – the more sodium delivered to the lumen and taken up by the principle cells, means more sodium pumped out via the Na-K-ATPase pump which pumps potassium in.
Distal nephron flow rate – increased delivery of sodium is the chief cause of increased flow rate (water follows). Bending of the cilia involved in the mechanosensitivity of the principle cells releases calcium and activates BK channels. Also increased flow leads to lower potassium concentrations on the luminal surface aka a higher concentration gradient and higher secretion.
Concentration of nonchloride anions
Dietary potassium
Explain diuretics unwanted side effect of increasing renal excretion of potassium.
Most of the increased potassium excretion is due to increased secretion in the distal nephron, NOT decreased re-absorption. Increased flow and increased delivery of sodium drives increased potassium secretion.
What are the two known reasons for the effects of acid-base status on potassium concentrations?
1) Elevations and depressions in extracellular concentration of H ions leads to and exchange with potassium.
2) Intracellular pH effects Na-K-ATPase and potassium channel activity.
Explain in general paradoxical potassium retention.
Normally – increased plasma K would stimulate K uptake by the Na-K-ATPase pumps in the principle cells. HOWEVER, when intracellular pH is LOW, the pump does not work. Therefore the principle cells respond inappropriately and do not effectively secrete the excess plasma potassium.
Dr. Hocine has eaten sooo many bananas that she is hyperK and has bad diarrhea. What part of her nephrone is responsible for the majority of the K excretion?
• The distal tubulus
Which tissue contains the most K in the body?
• Skeletal muscles
How does insulin affect K?
• It cause update of K into the cells
T/F hyperK is a trigger for insulin secretion?
• True
