Lec 47 K Balance Flashcards
How does reabsorption proximally affect distal reabsorption?
- if Na reabsorbed a lot in proximal it will affect how much K is absorbed in distal because less Na available
What percent of filtered K is net reabsorbed? Why is this important?
80-95%
there is such a huge range suggests need for K homeostatis
What factors balance to determine serum electrolyte conc?
- intake
- output
- movement between plasma and intracellular space
Where is majority of K stored in body?
90% of K stored in cells
What two things favor renal secretion?
- aldosterone
- elevated plasm K
What is immediate compensation for high plasma K?
- increased activity of NA-K ATPase
How does insulin play a role in K storage?
insulin increases Na-K ATPase action
makes sense since most K comes from food
What are the 2 things that trigger aldosterone release from adrenal?
- angiotensin II triggers release
2. high K triggers release
Over what time frame is most K excreted
by 6-8 hrs after ingesting
What happens to K in PT?
67% of K reabsorbed in PT passively with Na and H2O
What happens to K in loop of henle?
20% reabsorbed via Na/K/2Cl cotransporter in LOH [thick ascending limb]
What happens to K in distal convoluted tubule and collecting duct?
Aldosterone and high serum K lead to secretion via principal cells
What would happen to your serum K level if you lost early reabsorption?
you would be hypokalemic since this is where most of reabsorption occurs
In thick ascending limb what happens to K conc?
K conc decreases below that of blood because you are reabsorbing water and not reabsorbing K
Why is low K conc in thick ascending limb important for principal cell function?
- it means when you get to collecting duct there is a driving force for K to leave principal cells via K channel to enter lumen and be excreted
What determines amount of K secreted?
- concentration
- electrochemical gradients
What 4 ways does aldosterone increase principal cell K secretion?
- increases number of Na-K ATPase on basolateral side
- - increases Na out to interstitium
- - increases K into cell - increases potential of lumen
- increases activity of apical K channel = increase K secreted
- increases activity of apical Na channel = increase Na reabsorbed into cell
How does volume expansion alter K secretion?
- if eat a ton of salt and water you have to pee like crazy
- normally there is higher conc of K directly next to cell in lumen
- if increase volume get increased luminal flow
- decreases build up of K near cell so have even bigger K gradient = bigger driving force for K to enter lumen
What are the mech of hyperkalemia?
- high intake [uncommon]
- less going into cell
- too much going into cell
- less ouptut
What could cause too much K to leave intracellular space and thus leave you hyperkalemic?
in cancer undergo chemo causes cells to explode and get lots of K from thos cells into blood stream
What could cause decreased K output leading to hyperkalemia?
- kidney disease
- other physio problem takes presedence [ex. if hypotensive and high levels of aldosterone/angiotensin, you will aborb all Na proximally so don’t have Na distally to exchange with K to secrete K
- problem with regulatory hormones
How could being hypotensive lead to hyperkalemia?
will have high levels of aldosterone/angiotensin and you will absorb all Na proximally so don’t have Na distally to exchange with K to secrete K
What are the mech of hypokalemia?
- low intake [very rare]
- more K going into cells than leaving
- too much outflow
What are ways you could have more K going into cells than leaving?
- drugs –> like insulin cause K to go into cells
- alkalemia
