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
What inhibits K secretion?
Acidosis
What stimulated K secretion?
Alkalosis
What is BK?
Big K- Ca activated K channel on apical side of principle cells
What blocks ROMK?
Barium
During high flow, where is K going?
It is being secreted because luminal K is kept low
During low flow, where is K going?
K secretion is diminished and the gradient for K in the lumen build up, decreasing the concentration gradient so K stays in the blood
What is the role of cilia on K regulation?
At the base of cilium are Ca permeant channels. When there is flow, it deflects the cilium and the stress of it opens the Ca channels. This rise in Ca activates the BK channel and K exits into the tubule lumen
