Regulation of K Balance Flashcards
Role of Epinephrine in extrarenal regulation of plasma K+
Lowers serum K by uptake into cells of extrarenal tissues even while stimulating K+ excretion by kidney
differing responses for alpha and b receptor stimulation
Role of Insulin in extrarenal regulation of plasma K+
Stimulate Na/K ATPase causing flux of K+ into cells and efflux of Na+ from cellls
Insulin & Glucose administration can treat hyperkalemia
Role of Aldosterone in extrarenal regulation of plasma K+
- Renal
- Extrarenal
Renal: increase K+ excretion by kidney
Extrarenal: increase K+ secretion into intestinal fluids & saliva
Enhances acid excretion via production of systemic alkalosis (K is low)
Which factors enhance K+ uptake? how?
-Insulin and Beta- Catecholamines
both by activating Na/K ATPase (catecholamine is via cAMP)
- Alkalosis
“k is lo”
Which factors impairs K+ uptake? how?
-alpha catecholamines
opposite of beta
- acidosis
donnan effect; inhibit Na/K ATPase - Cell damage
release of intracellular contents
Which factors enhance K+ cell efflux? how?
-hyperosmolality
due to contraction of ICF volume and increased intracellular K+
- strenuous exercise
activating alpha catecholamines
Which factor has loose correlation/ effect on potassium?
external potassium balance
ration vs total body K+ until severe state
Filtered load equation
GFR * plasma concentration * % filterability
Plasma protein characteristics
- not filterable under normal circumstances
- any substance bound to plasma protein will not be filtered
PCT and PST
- what is always reabsorbed?
- what is mostly reabsorbed?
- what is secreted?
- major mechanism/ form of transport?
Always reabsorbed
- glucose
- amino acids
Most reabsorbed
- Na
- K
- Cl
- HCO3
- Ca
- P
Secreted
- cations and anions
- drugs, metabolites, creatinine, urate
Major mechanism
Na/K ATPase pump in basolateral membrane
K+ reabsorption in Proximal Tubule
- what does it effect
- locations
- similar to Na reabsorption
- does NOT play a direct role in regulation of K+ balance
- INDIRECT ROLE
- changing NaCl reabsorption has considerable effects on distal tubular flow and distal tubular Na+ delivery, which impacts K+ later on
PCT: S1 &S2
PST : S2 & S3
How does K+ get reabsorbed in PT? (8)
- driven by what?
1) Early PT, Na reabsorbed with HCO3
2) Cl gets let behind
3) Negative TEPD builds up
4) Cl is repelled and reabsorbed
5) Continued NaCL reabsorption drags water along (solvent drag)
6) Positive TEPD builds up as Cl- reabsorbs
7) Postive TEPD repels K
8) K reabsorbed paracellularly
driven by lumen-positive transepithelial potential difference (TEPD) - found in late proximal tubule
Early PCT reabsorbs a lot of sodium! Explain the effects of it?
Creates lumen-negative potential difference
pushes paracellular Cl- to get reabsorbed in the straight PT
reversal of the PD to a positive value will help push NA and K via paracellular reabsorption
Loop of Henle transport and medullary recycling steps (4)
1) K secreted in cortical CD
2) K reabsorbed by outer medulla CD and inner medulla CD
3) K+ floats in interstitium
4) K secreted into Late PT/descending thin limbs of LoH
Goal of Loop of Henle transport and medullary recycling
increase presence of medullary K
Purpose of Loop of Henle transport and medullary recycling
large K presence decreases NKCC2 reabsorption by TAL
-> enhanced Na-delivery to distal tubule-> stimulates NA reabsorption and K secretion-> helps you excrete K during dietary loading
Where is K+ secreted? reabsorbed?
BOTH in late DT and cortical CD
-according to needs of the body
What secretes K?
principal cells and beta-intercalated cells
Most important factors that stimulate potassium secretion
- by which channels
1) increased ECF (K)
2) aldosterone
3) increased tubular flow rate
potassium channels, epithelial sodium channels (EnaC), renal outer medullary potassium (ROMK)
What reabsorbs K?
alpha intercalated cells
Most important factors that stimulate potassium reabsoprtion
1) K deficiency, low K diet, hypokalemia
2) K loss through severe diarrhea
What is reabsorbed in these cells? What is secreted?
1) principal cells
2) alpha intercalated cells
3) beta intercalated cells
1) Principal cells
Reabsorbed: Na, H2O
Secretes: K
2) alpha intercalated cells
Reabsorbed: K+, HCO3
Secretes: H
3) beta intercalated cells
Reabsorbed: H, Cl
Secretes: K, HCO3
Factors that regulate K+ secretion (5)
Buildup of extracellular K
1) activate Na/K ATPase pump in basolateral membrane of principal cells
2) Reduced back-leakage of K+ from ICF to renal interstitium
3) activate synthesis of K channels and insertion into luminal membrane
4) activate aldosterone secretion
5) increased DT flow rate
How does increased flow rate enhance K secretion (2)?
dilutes K secreted in lumen -> increasing the K concentration gradient
Delivers more Na to DT for reabsorption-> gradient across the tubular cell rises-> K secretion is promoted
