Regulation of K, Ca, Mg, and Phosphate Balance Flashcards
(44 cards)
Extracellular fluid potassium concentration =
4.2 mEq/L
Maintaining the balance between intake and output of K+ is high dependent on which organ?
Kidneys
The movement of potassium between _____ and _____ compartments plays a major role in potassium homeostasis.
intracellular; extracellular
Where is 98% of the bodies potassium contained?
the cells
Factors that regulate the movement of K+ into and out of cells
-insulin
-aldosterone
-B-adrenergic stimulation
-acid-base balance
-cell lysis
-strenuous exercise
increased extracellular fluid osmolarity
Insulin and potassium balance
-important to help uptake of potassium INTO cells after a meal
Diabetes Mellitus = hypokalemia (injection helps)
Aldosterone and potassium balance
- increased potassium INTAKE stimulates aldosterone production
- aldosterone INCREASES cellular uptake of potassium and permeability of the luminal membrane
- Conn’s Syndrome = excess aldosterone; hypokalemia
- Addison’s Disease = deficient aldosterone; hyperkalemia
B-Adrenergic stimulation and potassium balance
- increased secretion of CATECOLAMINES (epinephrine)
- causes activation of B2 adrenergic receptors
- movement of potassium INTO cells
*treatment of HYPERTENSION with B-adrenergic receptor BLOCKERS (movement OUT of cells; causes hyperkalemia)
Acid-Base abnormalities and potassium balance
- Metabolic acidosis - INCREASES extracellular potassium levels; loss of K+ from cells (reduce activity of ATPase pump)
- Metabolic alkalosis - DECREASE in extracellular potassium levels
Cell lysis and potassium balance
- as cells are destroyed…
1) K+ in the cells is released into the extracellular compartment
2) significant MUSCLE DESTRUCTION or RBC LYSIS (sever hyperkalemia)
Strenuous exercise and potassium balance
- causes release of K+ from muscles
- Hyperkalemia can become severe if:
1) person is on B-adrogenic blocker
2) insulin deficiency
Increased extracellular fluid osmolarity and potassium balance
- causes fluid to flow from inside cells to extracellular compartment
- shift of fluid caues INCREASE in INTRAcellular K+
- diffusion of K+ out of cells
- INC extracellular K+ levels
*decreased = opposite effect
Factors that shift potassium INTO cells
- insulin
- aldosterone
- B-adrenergic stimulation
- alkalosis
- DEC extracellular fluid osmolarity
Factors that shift potassium OUT OF cells
- insulin deficiency
- aldosterone deficiency
- B-adrenergic blockers
- acidosis
- cell lysis
- strenuous exercise
- INC extracellular fluid osmolarity
Renal potassium excretion is determined by:
rate of potassium
1) filtration (at glomerulus)
2) reabsorption (tubules)
3) secretion (tubules)
Rate of K+ filtration at glomerular capillaries =
756 mEq/day
Tubular handling of K+ in proximal tubules = ?%
65% reabsorbed here
Tubular handling of K+ in THICK ascending loop of Henle = ?%
25-30% reabsorbed here
Where are daily variations of K+ excretion handled?
- late distal tubules*
- cortical collecting tubules*
by PRINCIPLE cells (stimulated by aldosterone)
2 step process of principle cells
1) basolateral cell membrane the ATPase pump moves K+ from the blood INTO the cell and Na+ OUT OF the cell
2) on the luminal membrane, PASSIVE DIFFUSION of K+ from the inside of the cell to the TUBULAR LUMEN
3 factors that control K+ secretion by the Principle Cells
1) activity from ATPase pump
2) electrochemical gradient for K+ secretion from blood to tubular lumen
3) permeability of the luminal membrane for K+
What happens when there is K+ depletion in the system?
- NO secretion of K+ in the late distal tubule and collecting tubule
- reabsorption of K+ occurs in INTERCALATED CELLS
Factors that STIMULATE K+ secretion
- INCREASED extracellular fluid K+
- INCREASED aldosterone
- INCREASED tubular flow rate
Factors that DECREASE K+ secretion
-INCREASED H+ ion concentraion (ACIDOSIS)
