Regulation of K, Ca, Mg, and Phosphate Balance

Question 1

Extracellular fluid potassium concentration =

Answer 1

4.2 mEq/L

Question 2

Maintaining the balance between intake and output of K+ is high dependent on which organ?

Answer 2

Kidneys

Question 3

The movement of potassium between _____ and _____ compartments plays a major role in potassium homeostasis.

Answer 3

intracellular; extracellular

Question 4

Where is 98% of the bodies potassium contained?

Answer 4

the cells

Question 5

Factors that regulate the movement of K+ into and out of cells

Answer 5

-insulin
-aldosterone
-B-adrenergic stimulation
-acid-base balance
-cell lysis
-strenuous exercise
increased extracellular fluid osmolarity

Question 6

Insulin and potassium balance

Answer 6

-important to help uptake of potassium INTO cells after a meal

Diabetes Mellitus = hypokalemia (injection helps)

Question 7

Aldosterone and potassium balance

Answer 7

• 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

Question 8

B-Adrenergic stimulation and potassium balance

Answer 8

• 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)

Question 9

Acid-Base abnormalities and potassium balance

Answer 9

• Metabolic acidosis - INCREASES extracellular potassium levels; loss of K+ from cells (reduce activity of ATPase pump)
• Metabolic alkalosis - DECREASE in extracellular potassium levels

Question 10

Cell lysis and potassium balance

Answer 10

• as cells are destroyed…
  1) K+ in the cells is released into the extracellular compartment
  2) significant MUSCLE DESTRUCTION or RBC LYSIS (sever hyperkalemia)

Question 11

Strenuous exercise and potassium balance

Answer 11

• causes release of K+ from muscles
• Hyperkalemia can become severe if:
  1) person is on B-adrogenic blocker
  2) insulin deficiency

Question 12

Increased extracellular fluid osmolarity and potassium balance

Answer 12

• 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

Question 13

Factors that shift potassium INTO cells

Answer 13

• insulin
• aldosterone
• B-adrenergic stimulation
• alkalosis
• DEC extracellular fluid osmolarity

Question 14

Factors that shift potassium OUT OF cells

Answer 14

• insulin deficiency
• aldosterone deficiency
• B-adrenergic blockers
• acidosis
• cell lysis
• strenuous exercise
• INC extracellular fluid osmolarity

Question 15

Renal potassium excretion is determined by:

Answer 15

rate of potassium

1) filtration (at glomerulus)
2) reabsorption (tubules)
3) secretion (tubules)

Question 16

Rate of K+ filtration at glomerular capillaries =

Answer 16

756 mEq/day

Question 17

Tubular handling of K+ in proximal tubules = ?%

Answer 17

65% reabsorbed here

Question 18

Tubular handling of K+ in THICK ascending loop of Henle = ?%

Answer 18

25-30% reabsorbed here

Question 19

Where are daily variations of K+ excretion handled?

Answer 19

• late distal tubules*
• cortical collecting tubules*

by PRINCIPLE cells (stimulated by aldosterone)

Question 20

2 step process of principle cells

Answer 20

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

Question 21

3 factors that control K+ secretion by the Principle Cells

Answer 21

1) activity from ATPase pump
2) electrochemical gradient for K+ secretion from blood to tubular lumen
3) permeability of the luminal membrane for K+

Question 22

What happens when there is K+ depletion in the system?

Answer 22

• NO secretion of K+ in the late distal tubule and collecting tubule
• reabsorption of K+ occurs in INTERCALATED CELLS

Question 23

Factors that STIMULATE K+ secretion

Answer 23

• INCREASED extracellular fluid K+
• INCREASED aldosterone
• INCREASED tubular flow rate

Question 24

Factors that DECREASE K+ secretion

Answer 24

-INCREASED H+ ion concentraion (ACIDOSIS)

Question 25

how does increased extracellular fluid potassium concentration increase potassium secretion?

Answer 25

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

Question 26

Aldosterone-potassium control system

Answer 26

• INCREASE in plasma K+ concentration
• STIM of aldosterone secretion
• INC levels of blood ald levels
• INC K+ excretion
• extracellular K+ levels return to normal

Question 27

How does increased tubular flow effect potassium secretion?

Answer 27

• 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

Question 28

T/F: Chronic acidosis leads to an INCREASE in potassium secretion.

Answer 28

TRUE - decreased Na+ and water reabsorption in the distal tubule; causes increase tubular flow; increases K+ secretion

Question 29

T/F: Acute acidosis leads to an INCREASE in potassium secretion.

Answer 29

FALSE (only chronic) - decreases

Question 30

T/F: Alkalosis INCREASES potassium secretion.

Answer 30

True

Question 31

T/F: All of the calcium in blood can be filtered out at the glomerulus.

Answer 31

FALSE!!! - half of blood calcium is bound to proteins; therefore, only half can be filtered at the glomerulus

Question 32

What percent of calcium that is filtered at the glomerulus is reabsorbed in the proximal tubule?

Answer 32

~65%

Question 33

What percent of calcium that is filtered at the glomerulus is reabsorbed in the loop of Henle?

Answer 33

~30%

Question 34

What percent of calcium that is filtered at the glomerulus is reabsorbed into the blood stream?

Answer 34

~99%

Question 35

Which hormone is the major regulator of calcium in the renal system?

Answer 35

PTH (parathyroid hormone)

-influences reabsorption in the loop of Henle and DISTAL tubule

Question 36

T/F: PTH influences reabsorption of calcium at the proximal tubule.

Answer 36

FALSE!!! - only loop of Henle and DISTAL tubule

Question 37

What effect does alkalosis have on calcium regulation

Answer 37

INCREASES reabsorption

Question 38

What effect does acidosis have on calcium regulation?

Answer 38

DECREASES reabsorption

Question 39

Factors that STIMULATE calcium excretion

Answer 39

• DECREASED PTH levels
• INCREASED ECF volume
• INCREASED blood pressure
• INCREASED H+ (acidosis)

Question 40

Factors that DECREASE calcium excretion

Answer 40

• INCREASED PTH levels
• DECREASED ECF volume
• DECREASED blood pressure
• DECREASED H+ (alkalosis)

Question 41

What percent of Magnesium is absorbed by the digestive system?

Answer 41

~50% (more than needed for daily function)

Question 42

T/F: Taking magnesium supplements can be dangerous.

Answer 42

TRUE!!! - upper limit to Mg excretion (at glomerulus)

Question 43

Most reabsorption of Phosphate happens in the _____

Answer 43

Proximal tubule (~80% via sodium phosphate co-transporters)
^remainder is picked up in DISTAL tubule

Question 44

T/F: Diets low in phosphate stimulate the production of additional transport capacity.

Answer 44

TRUE!