3. Regulation of K, Ca, Pi, and Mg Balance DSA

Question 1

What is the effect to muscle cells of hyperkalemia?

Answer 1

Initial spasticity followed by muscle weakness resulting in paralysis.

Question 2

What is the recommended dietary intake of phosphorus?

How much of that (net) is absorbed per day?

Answer 2

1500 mg

900 mg (net) is absorbed per day

Question 3

What would a decrease in potassium do to the acid-base balance of a cell?

Answer 3

The decrease in potassium causes acidosis.

Question 4

What are the primary loss routes of potassium?

Answer 4

Mostly urine, some feces

60 mmol per day through urine

10 mmol per day through the feces

Question 5

What are the main (high-yield seeming) symptoms of magnesium depletion? (Three things)

Answer 5

Loss of bone density

Muscle cramps

Arrhythmia

Question 6

What would you expect if you saw peaked T-wave on an EKG?

Answer 6

Hyperkalemia

Question 7

What is the response of cardiac muscle cells to hyperkalemia and hypokalemia?

Answer 7

Hyperkalemia results in bradycardia (hyperpolarization)

Hypokalemia results in tachycardia (hypopolarization)

Question 8

What is the effect of increased calcium on muscular excitability?

Answer 8

Decreased muscular excitability.

(Calcium acts opposite to potassium on the resting membrane potential of muscle cells)

Question 9

What is the recommended daily dose of calcium?

Answer 9

1000 mg per day

(It is difficult to absorb more than 500 mg at one time, so supplementation should be broken up into two doses)

Question 10

What are the three listed common causes of hyperkalemia?

Answer 10

Excessive intake

Tissue release (from rhabdomyolysis, burns, hemolysis)

Shifts from ICF to ECF (insulin deficiency, acidosis, hyperglycemia)

Question 11

What would be the effect of low plasma potassium concentration on vascular resistance?

Answer 11

Low plasma potassium concentration results in vasoconstriction

Question 12

What are the primary loss routes of phosphate?

Answer 12

Mostly urine, some feces

Question 13

What is the effect to muscle cells of hypokalemia?

Answer 13

Hyperpolarization resulting in muscle weakness, paralysis, intestinal distention, and respiratory failure

Question 14

Does hyperkalemia hypopolarize or hyperpolarize the resting membrane potential in most cells?

Answer 14

Hyperkalemia hypopolarizes the membrane.

(More potassium in the extracellular fluid results in a lessened differential of potassium across the membrane.)

Question 15

What is the approximate intracellular concentration of potassium?

Answer 15

150 mEq/L

Question 16

Does hypokalemia hyper-polarize or hypo-polarize resting membrane potentials?

Answer 16

Hypokalemia hyperpolarizes the resting membrane.

(Less potassium in the extracellular space means a greater differential of potassium across the membrane)

Question 17

What are the primary loss routes of magnesium?

Answer 17

Mostly feces, some urine

Question 18

In what forms is magnesium capable of circulating in the bloodstream?

Answer 18

Diffusible magnesium complexes

Non-diffusible (protein-bound) magnesium

Free magnesium

Question 19

What are the primary loss routes for calcium?

Answer 19

Primarily stool, some urine

Question 20

What are the four major intracellular locations given for potassium storage?

Answer 20

Muscle cells

Bone

Liver

Erythrocytes

(In that order)

Question 21

What is the definition of hypokalemia?

Answer 21

Plasma potassium <3.7 mEq/L

Question 22

What is pseudohyperkalemia?

Answer 22

Artificially high plasma potassium lab results, due to lysis of red blood cells when blood is drawn.

Question 23

What is the definition of hyperkalemia?

Answer 23

Plasma potassium >5.2 mEq/L

(>10 mEq/L is lethal)

Question 24

What would loss of potassium due to the volume of the cell?

Answer 24

The cell would shrink

Question 25

How do PTH, calcitriol, and calcitonin affect the amount of calcium in the body?

Answer 25

Calcitonin stores calcium in bones.

Calcitriol and PTH pull calcium out of bones.

Calcitonin encourages secretion of calcium by the kidneys.

Calcitriol, and PTH work together to block excretion of calcium through the kidneys.

Question 26

What is the normal range for plasma potassium concentration?

Answer 26

3.5 to 5.0 mEq/L

Question 27

Where is the majority of phosphate kept in the body?

Answer 27

In the bone

Question 28

What maintains the “thirtyfold difference” in concentration between intracellular and extracellular potassium?

Answer 28

Na/K ATPase (expressed ubiquitously)

Na/K/2Ca channel

K-channels

Question 29

What would a significant decrease in potassium inside a cell do to the rate of protein synthesis?

Answer 29

It would decrease. Potassium is essential for protein synthesis

Question 30

Where is the majority of potassium stored in the body?

Answer 30

In the muscle cells

Question 31

What are the four main regulators of phosphate metabolism and their actions?

Answer 31

Dietary: amount of phosphate ingested.

Calcitriol: reabsorbs phosphate from the bone, and helps phosphate uptake from the G.I.

PTH (parathyroid hormone): reabsorbs phosphate from the bone, and increases calcitriol production (indirectly increases G.I. absorption).

Renal tubular reabsorption: PTH increases phosphate excretion by the kidneys (opposite of calcium)

Question 32

What are the four listed common causes of hypokalemia?

Answer 32

Vomiting and diarrhea

Insulin excess

Deficiency of potassium

Alkalosis

Question 33

What is the effect of a high plasma potassium concentration on vascular resistance?

Answer 33

High plasma potassium concentration results in vasodilation

Question 34

What is the normal range for serum magnesium?

What is the normal range for free serum magnesium?

Answer 34

Serum magnesium: 1.8 to 2.2 mg/dL

Free serum magnesium: 0.8-1.0 mEq/L