K homeostasis Flashcards
What is resting membrane potential determined by?
Membrane K conductance
What is the acute (non renal) response to ingestion of K rich meal?
K and glucose increase which stimulates ATP in pancreatic beta cells K also has a positive effect on insulin release. It also activate Na/K ATPase which increases uptake of K and ECF K goes back to normal
How does K balance remain when K is ingested from food?
The excess must be excreted
What are long term regulation of ECF [K]?
- Fecal loss
- Renal excretion
How much K is excreted in urine?
Dietary intake- (amt lost in feces + amt lost in sweat)
What is the goal of K homeostasis?
A constant amount and distribution in both ECF and ICF
Does extracellular K have a large or narrow range for physiological functions?
Narrow
How does the kidney regulate ECF K levels?
- Filtration
- Transport
- Excretion
What factors modulate ECF K levels?
- K in luminal fluid
- ECF and ICF pH
- Flow of fluid through collecting duct
What happens to K in the Proximal tubule?
K is absorbed due to a concentration driven paracellular absorption. As it moves down the PT water is being absorbed increasing K concentrations and the farther down the PT the more positively charged the lumen is driving K further through the tight junctions
How much K is absorbed in the PT in normal individuals?
60-80%
How is K absorbed in the TALH?
ROMK as well as K back leak producing a lumen positive pd and drives the cations (k and Na) across the junctions
What percent of K is absorbed by TALH in normal individuals?
5-25%
How is K absorbed by CD alpha intercalated cells?
Transcellular through H/K pump
How is K secreted in principle cells of the CD?
High plasma K stimulates aldosterone as well and increase insulin secretion which then stimulates Na/K ATPase. This increase the intracellular K concentration. Aldosterone stimulates ROMK and BK on the apical side and pumps it out into the lumen
