Calcium, magnesium, phosphorous

Question 1

how much of the calcium distribution is extracellular? how much of that is free? bound?

Answer 1

• 1% is extracellular (50% free, 50% bound)

Question 2

what is the relationship between albumin and calcium?

Answer 2

for every 1g / dL drop in serum albumin below 4 g / dL, measured serum calcium decreases by 0.8 mg /dL

Question 3

when you see that calcium is low, what should you think about?

Answer 3

albumin levels

Question 4

what are the calcium regulatory hormones?

Answer 4

• PTH
• calcitonin
• vitamin D

Question 5

what are the roles of PTH? what is the net effect?

Answer 5

• increase osteoclastic bone resorption of calcium and phosphate
• increase DCT calcium reabsorption
• decreases PCT phosphate reabosorption
• increases gut absorption of calcium

NET EFFECT: increased serum calcium and decreased serum phosphate

Question 6

what are the roles of calcitonin? what is the net effect?

Answer 6

• inhibits osteoclastic bone resorption
• decreases renal tubular reabsorption of calcium and phosphate
• decreases gut absorption of phosphate

NET EFFECT: decreased serum calcium and phosphate

Question 7

what are the roles of vitamin D? what is the net effect?

Answer 7

• increase intestinal absorption of calcium and phosphate
• increase bone resorption of calcium and phosphate by increasing osteoclast activity
• increase renal reabsorption of calcium and phosphate
• decrease production of PTH

NET EFFECT: increased serum calcium and phosphate

Question 8

what are the signs and symptoms for hypercalcemia?

• CNS
• neuromuscular
• CV
• renal
• GI
• metastatic calcification?

Answer 8

• CNS: lethargy, psychosis, coma
• neuromuscular: myalgias, weakness
• CV: bradycardia, short QT
• renal: polyuria, decreased GFR, nephrolithiasis, nephrocalcinosis
• GI: anorexia, nausea, constipation
• metastatic calcification: yes

Question 9

what does hypocalcemia do to the QT interval?

Answer 9

prolongs

Question 10

what are the ddx for hypercalcemia?

Answer 10

• primary hyperparathyroidism
• malignancy
• drug induced
• granulomatous disease / immobilization / acidosis

Question 11

what drugs / medications can cause hypercalcemia?

Answer 11

• vitamin A
• vitamin D
• thiazide diuretics
• lithium
• milk-alkali

Question 12

how do thiazide diuretics cause drug induced hypercalcemia?

Answer 12

increased renal reabsorption of calcium

Question 13

how does lithium cause drug induced hypercalcemia?

Answer 13

• failure of suppression of PTH secretion by calcium

- hypocalciuria

Question 14

what are the treatment options for hypercalcemia?

Answer 14

• ECF volume restoration
• loop diuretics
• bisphosphonates
• calcitonin
• glucocorticoids
• dialysis

Question 15

what are the mild / moderate / severe levels for hypocalcemia?

Answer 15

• mild: 8.0-8.5
• moderate: 7.0-7.5
• severe: under 7.0

Question 16

what are the signs and symptoms of hyocalcemia?

Answer 16

• paresthesias
• tetany
• long QT, arrhythmias
• seizures

Question 17

vitamin D dependent rickets type 1 is due to a deficiency in what enzyme?

Answer 17

1-alphahydroxylase

Question 18

vitamin D dependent rickets type 2 is due to a mutation in what receptor?

Answer 18

vitamin D receptor

Question 19

what are the roles of phosphorous?

Answer 19

• structural component of most biological membranes
• nucleotides and nucleic acids
• signal transduction
• temporary storage and transfer of the energy derived from metabolic fuel
• enzyme regulation: activation of many catalytic proteins by phosphorylation

Question 20

what are the symptoms of hyperphosphatemia?

Answer 20

• hypocalcemia-related: muscle spasms, perioral numbness

- related to underlying condition: fatigue, SOB, edema, lack of appetite, N/V

Question 21

what are the etiologies of hyperphosphatemia?

Answer 21

• acute phosphate load

- increased tubular reabsorption of phosphate

Question 22

what are the symptoms of severe hypophosphatemia?

Answer 22

• weakness
• bone pain
• rhabdomyolysis
• mental status changes

Question 23

what are the etiologies of hypophosphatemia?

Answer 23

• inhibition of distal tubular reabsorption of calcium and magnesium (hypercalciuria)
• intracellular phosphate depletion

Question 24

what are the hematological effects of hypophosphatemia?

Answer 24

• RBCs: hemolysis, RBC rigidity
• WBCs: decreased phagocytosis and chemotaxis
• platelets: defective clot retraction, thrombocytopenia

Question 25

what conditions are associated with symptomatic hypophosphatemia?

Answer 25

- chronic alcoholism - refeeding syndrome - chronic ingestion of antacids

Question 26

what is the most common cause of hyperphosphatemia? why is this?

Answer 26

- renal failure | - urinary excretion cannot balance phosphate intake

Question 27

what are the roles of magnesium?

Answer 27

- enzyme cofactor - required for oxidative phosphorylation - bone development - DNA, RNA synthesis - transport of calcium and potassium across cell membranes

Question 28

what are the symptoms of hypomagnesemia?

Answer 28

- nystagmus - fatigue - seizures - muscle spasms - weakness: diaphragm - numbness

Question 29

what does hypomagnesemia do to the QT interval?

Answer 29

prolongs