Regulation of K, Ca, Mg, and Phosphate Balance Flashcards
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)
how does increased extracellular fluid potassium concentration increase potassium secretion?
1) stimulate ATPase pumps in basolateral membrane
2) increase gradient of K+ in cell compared to interstitial fluid
3) increased K+ also increases aldosterone secretion by ADRENAL CORTEX
Aldosterone-potassium control system
- INCREASE in plasma K+ concentration
- STIM of aldosterone secretion
- INC levels of blood ald levels
- INC K+ excretion
- extracellular K+ levels return to normal
How does increased tubular flow effect potassium secretion?
- STIMULATES K+ secretion
- tubular flow rate increases with:
1) volume expansion
2) high sodium intake (helps preserve normal K+ secretion during high Na+ intake)
3) treatment with some diuretics
T/F: Chronic acidosis leads to an INCREASE in potassium secretion.
TRUE - decreased Na+ and water reabsorption in the distal tubule; causes increase tubular flow; increases K+ secretion
T/F: Acute acidosis leads to an INCREASE in potassium secretion.
FALSE (only chronic) - decreases
T/F: Alkalosis INCREASES potassium secretion.
True
T/F: All of the calcium in blood can be filtered out at the glomerulus.
FALSE!!! - half of blood calcium is bound to proteins; therefore, only half can be filtered at the glomerulus
What percent of calcium that is filtered at the glomerulus is reabsorbed in the proximal tubule?
~65%
What percent of calcium that is filtered at the glomerulus is reabsorbed in the loop of Henle?
~30%
What percent of calcium that is filtered at the glomerulus is reabsorbed into the blood stream?
~99%
Which hormone is the major regulator of calcium in the renal system?
PTH (parathyroid hormone)
-influences reabsorption in the loop of Henle and DISTAL tubule
T/F: PTH influences reabsorption of calcium at the proximal tubule.
FALSE!!! - only loop of Henle and DISTAL tubule
What effect does alkalosis have on calcium regulation
INCREASES reabsorption
What effect does acidosis have on calcium regulation?
DECREASES reabsorption
Factors that STIMULATE calcium excretion
- DECREASED PTH levels
- INCREASED ECF volume
- INCREASED blood pressure
- INCREASED H+ (acidosis)
Factors that DECREASE calcium excretion
- INCREASED PTH levels
- DECREASED ECF volume
- DECREASED blood pressure
- DECREASED H+ (alkalosis)
What percent of Magnesium is absorbed by the digestive system?
~50% (more than needed for daily function)
T/F: Taking magnesium supplements can be dangerous.
TRUE!!! - upper limit to Mg excretion (at glomerulus)
Most reabsorption of Phosphate happens in the _____
Proximal tubule (~80% via sodium phosphate co-transporters) ^remainder is picked up in DISTAL tubule
T/F: Diets low in phosphate stimulate the production of additional transport capacity.
TRUE!
