Regulation of K+ Balance + Intro DSA Flashcards
How does the cardiac conduction system respond to hyperkalemia?
the opposite of other cells!
hyperkalemia –> hyperpolarizes membrane –> high T waves
What are the most important factors that stimulate potassium secretion?
- Increased K in ECF
- Aldosterone
- Increased tubular flow rate
What is pseudohyperkalemia?
artificially high plasma K levels due to lysis of RBCs while blood is drawn
How does hyperkalemia affect membrane potential?
hypopolarizes the cell –> easier to depolarize and make action potential
How does hypercalcemia affect membrane potential?
increases threshold –> cells are less excitable
What is alkalemia?
physiologically high blood pH
How does decreased flow rate affect K+?
K+ concentration builds up earlier in tubule –> concentration gradient decreased –> K+ secretion slows
What are the most important factors that stimulate K reabsorption?
- K+ deficiency, low K+ diet, hypokalemia
- K+ loss through severe diarrhea
Where is K+ found throughout the body?
98% intracellular
- 80% muscle cells
- 20% other cells
2% extracellular
How do beta-catecholamines affect K?
enhance cell uptake
+ Na-K-ATPase via + cAMP
How does increased flow rate affect K+?
increased flow rate dilutes K+ secreted into lumen –> increases K+ concentration gradient bc K+ is washed away –> delivers more Na+ to DT for reabsorption –> K+ secretion is promoted
How does aldosterone affect serum K+ concentration?
lowers serum K
renal: increases K+ excretion
extrarenal: increases K+ secretion into intestinal fluids and saliva; enhances acid excretion via production of systemic alkalosis
What is the normal dietary intake of calcium for an adult?
1000 mg/day
absorption best at <500 mg
How does acute acidosis affect K+
decreased activity of Na-K-ATPase pump
decreased K+ brought into cells from IF
decreased K+ secretion
end result = hyperkalemia
What occurs to K+ in the late DT and cortical CD?
secreted or reabsorbed according to the needs of the body
Where is phophate distrubuted in the body?
85% bone
14% cells
1% serum
How does the heart respond to hypokalemia?
the opposite of other cells
hypokalemia –> hypopolarized –> low T wave and tachycardia
Where is magnesium distributed in the body?
50% in bone
49% in ICF
1% in ECF
How does chronic acidosis affect K+?
chronic acidosis decreases reabsorption of water and solutes by PT by inhibiting NaKATPase –> increases tubular flow –> RAAS stimulated due to lack of water reabsorption –> ends up increasing K+ secretion
What is normal total serum Mg?
Free?
total = 1.8 mEq/L
Free = 0.8 - 1.0 mEq/L
How does cell damage affect K?
impaired cell uptake
release of intracellular contents
How does increased NaCl reabsorption upstream affect K+ secretion downstream?
decreases it
bc less Na delivery to CNT and CCD –> decreases Lumen-negative potential difference
What happens to K+ in Beta intercalated cells?
H+ /K+ antiporter on basolateral surface pulls in K+ from IF –> K+ flows down gradient into tubular lumen = K+ secreted
BS = beta secretes
How does hyperosmolality affect K?
enhanced cell eflux H2O goes out of cells to balance –> K+ concentration in cells increases –> K+ goes out of cells down its gradient
What is the recommended phosphorus intake?
How much is actually absorbed?
1500 mg dietary intake required
1100 mg absorbed
200 mg secreted into gut
~net 900 mg phosphorus absorbed per day
What is K+ resorption like in the proximal tubule (in general)?
similar to Na+ resorption
plays an indirect role in regulation of K+ balance via NaCl reabsorption –> affects distal tubular flow –> impacts K+ later on
What happens to K+ in principal cells of the collecting duct?
Na-K-ATPase pump on basolateral side pulls K in from the IF –> K exits and is secreted into tubular lumen via BK and ROMK ENaC pulls in Na from lumen and is target of aldosterone
What happens to K+ in alpha-intercalated cells?
Alpha reAbsorbs K
H+/K+ antiporter on apical surface pulls in K+ –> goes down gradient and is reabsorbed
What is the equation for filtered load?
GFR x plasma concentration x %filterability
How does acute alkalosis affect K+?
increased activity of Na-K-ATPase
increased K brought into cells from IF
Increased K+ secretion
end result = hypokalemia (K+ is lo)
What are the 4 steps of LoH transport and recycling of K+?
- K+ secreted into cortical collecting duct
- K+ reabsorbed by OMCD and IMCD
- K+ floats in interstitium
- K+ secreted into Late PT/descending thin limbs of LoH
Via what mechanism is K+ reabsorbed in the PT?
paracellularly
How does hypocalcemia affect membrane potential?
decreases threshold –> cells are more excitable
hypocalcemic tetany/spasticity
How do alpha catecholamines affect K?
impaired cell uptake
- Na-K-ATPase via - cAMP
How does epinephrine affect serum K+ concentrations?
lowers serum K increases uptake into extrarenal cells stimulates K excretion by the kidney
(differing response for alpha vs beta receptors)
How do high sodium and flow rate relate?
High sodium or decreased aldosterone inhibits K+ secretion
High flow rate increases K+ secretion
counteract/balance each other out
How does hypokalemia affect membrane potential?
hyperpolarizes cell – harder to make action potential
What is alkalosis?
decrease in H+ ion concentration in the ECF
acute process
How does anion deliver affect K+?
increases K+ secretion
How does strenuous exercise affect K?
enhanced cell efflux
+ alpha catecholamines
What is the goal of K+ recycling?
increase presence of medullary K+ –> decreases NKCC reabsorption by TAL –> enhanced Na delivery to distal tubule –> stimulates Na reabsorption and K+ secretion = helps you excrete more K+ during dietary load!!!
What is the normal range of plasma K+ concentration?
3.5 - 5.0 mEq/L
How does Insulin affect serum K+ concentration?
lowers serum K stimulates Na-K-ATPase –> flux of K+ into cells and efflux of Na+ out of cells
*insulin and glucose administration can treat hyperkalemia
How is K+ reabsorption driven in the PT?
In early PT, Na reabsorbed primarily w/ HCO3- Cl- gets left behind –> - charges build up (TEPD) –> Cl- is repelled and reabsorbed –> water dragged along –> positive TEPD builds up as Cl- reabsorbed –> positive TEPD repels K+ –> K+ reabsorbed PARACELLULARLY
