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
