Regulation of K Balance Flashcards
where is most of the bodies K?
inside cells
what is the normal range for plasma K
3.5-5 mM
what is the chief determinant of ICFV?
potassium
what is responsible for the uneven K distribution in the body?
the Na/K pump- 3 Na out for 2 K in
describe the reaction kinetics of the Na/K pump compared to reactant concentrations
the K site is saturated at 1 mM concentrations, much lower than plasma concentrations. however, the Na site is saturated at approximately the internal [Na}, so deviations can alter function
what is responsible for MRP
K
describe insulins effects on K balance
increases K uptake by cells by 3 mechanisms
- directly stimulates Na/K pump
- insulin increases glucose uptake, which is then converted to glucose-6-phosphate. this requires phosphate, which is cotransported with Na, allowing for an uptick in the Na/K pump.
- activates the Na/H exchanger, which then activates the Na/K pump
what treatment may be given to correct hyperkalemia?
insulin with glucose
why is there a net intracellular K loss during exercise?
the AP consists of a rapid Na influx and a slower K leak. The K channels are open longer and thus more K is lost than Na can be used to feed Na/K pump.
describe the effects of catecholamines on the Na/K pumo
norepinephrine- alters b-receptors, inhibiting the Na/K pump and promoting extracellular K
epinephrine- acts on b-receptors, stimulating the Na/K pump and promoting K uptake
how does the body deal with potential K swings during exercise?
it releases epinephrine before to prevent hyperkalemia and norepinephrine after to prevent hypokalemia
how does acid-base balance effect K levels?
model: when one K enters, one H leaves
therefore, as cells become K deficient, they become acidic and vice versa
how does plasma osmolality affect K balance?
when the plasma is hyperosmotic, it causes cell shrinkage, concentrating [K], and some must leave the cell.
in hypotonic environments, the cells swell, causing a dilution of the K and an uptake.
describe K transport in the PT
2/3 of the filtered K is reabsorbed passively, through paracellular pathways caused by solvent drag and positive voltage in the the distal PT
describe K transport in the LOH
descending- K is passively secreted d/t high [ ] in medulla
ascending- almost all remaining K, including secretions, is reabsorbed
describe K transport in the DT and CCD
cortical collecting duct
K transport here is bidirectional, secretion is the dominant process under normal K intake
principle cells- have the luminal ENaC channels, K secretion is coupled to Na reabsorption. the movement of ions is tied to the Na/K pump, creating a negative voltage luminally and facilitating K secretion
a-intercalated- reabsorb K in exchange for H- H/K-ATPase
describe K transport in the MCD
medullary collecting duct
transport is always reabsorption
reabsorbs by both passive and active routes.
active- luminal H/K-ATPase- more superficial
passive- deeper
describe the effect of plasma [K] on renal function
2 effects
- directly stimulates K secretion in DT and CCD=
- the adrenal gland can sense changes and secretes aldosterone, which causes secretion
how does the rate of [na] absorption affect k dynamics?
in the DT and CCD, the rates are coupled together, so an increase in Na reabsorption causes an increase in K secretion
aldosterone can be stimulated in 2 ways. how do the effects differ?
- RAAS- stimulated by low Na, causes increases in Na reabsorption in the proximal tubule, so less Na is seen at the CCD and DT, sparing K
- adrenal gland- stimulated by elevated K, this does not activate the PT and only the coupled Na/K transport in the CCD and DT responds, resulting in K wasting
describe the effect of anion composition on K transport
part of K secretion is mediated by a positive luminal voltage. Cl will also respond to this voltage, leaving the lumen, and lessening the strength. the paracellular pathway is impermeable to other anions. after the consumption of a meal, there is both more K and more anions, so the lumen will be more negative and K secretion will be enhanced
describe the effect of flow rate on K
two mechanisms
- slow flow allows secretion to reach an equilibrium, halting secretion. continuous flow washes away luminal K and increases secretion
- flow bends cilia on principal cells, stimulating K transport
describe the effect of ADH on K transport
because increased ADH decreases flow rate, you’d expect a decreased K secretion as well. ADH also stimulated k secretion to cancel out its flow mediated effect and allow K and water regulation to occur independently
how does pH affect K transport in the kidney
secretion is favored under alkaline conditions and inhibited under acidic ones
describe how to interpret transtubular K gradient
normal values are within 8-9. if someone is hyperkalemic, they should have an elevated TTKG, indicating a normal kidney response. if it is low, this is inappropriate, and kidney function is impaired.
