52 Calcium metabolism disorders

Question 1

Where are phosphate and magnesium predominantly found?

Answer 1

Intracellularly.

Question 2

What are the three key controlling factors of calcium?

Answer 2

PTH.
Vitamin D.
Klotho.

Question 3

Which form of calcium is physiologically active?

Answer 3

Ionised calcium.

Question 4

Which protein is used to bound Ca?

Answer 4

Albumin.

Question 5

How is calcium complexed? (2)

Answer 5

Calcium phosphate.

Calcium citrate.

Question 6

What is ‘adjusted calcium’?

Answer 6

Calcium values that have been adjusted for changes in albumin levels.

Question 7

What is the distribution of calcium in the plasma?

Answer 7

Ca: 2.3mmol/L.
Ionised: 1.3mmol/L.
Bound: 0.95mmol/L.
Complexed: 0.05mmol/L.

Question 8

How is calcium measured?

What are the drawbacks of this?

Answer 8

Total calcium.
Affected by albumin concentration.
pH influences ionised calcium.

Question 9

How and why does Ca distribution change with pH?

Answer 9

Ca and H+ compete for Albumin binding sites.

Acidosis lowers bound Ca levels, increasing ionised Ca levels.

Question 10

What is the clinical implication of Ca and H+ competing for albumin?

Answer 10

Alkalosis may stimulate tetany.

Question 11

How is vitamin D made?

Answer 11

UVB converts pre D2 to D3. Absorbed into blood (or from gut).
Liver concerts it to 25(OH)D.
Kidney converts it to 1α25(OH)D -the active form.

Question 12

What are the functions of vitamin D? (4)

Answer 12

Increases intestinal Ca and phos absorption.
Increases bone mineralisation.
Induces immune cell differentiation.
Works against tumour microenvironment.

Question 13

How do vitamin D levels change with age and body fatness?

Answer 13

Decreases.

Question 14

How does PTH act in homeostasis?

Answer 14

PTH increases bone Ca release and GI absorption. High Ca switches off PTH.
PTH also decreases Ca clearance from kidney and increase PO4- excretion.

Question 15

What are the causes of hypocalcaemia? (5).

Answer 15

Hypoproteinaemia.
Vit D deficiency.
Hypoparathyroidism (or Mg deficiency).
Inadequate intake.
Pseudohypoparathyroidism.

Question 16

What are the causes of hypercalcaemia? (6).

Answer 16

Hyperparathyroidism.
Malignancy.
Drugs.
Vit D excess - sarcoidosis.
Bone disease.
Immobilisation.

Question 17

What are the causes of phosphate deficiency? (3).

Answer 17

Hyperparathyroidism.
Excess losses: renal damage, GI, diabetes.
Poor intake.

Question 18

What are the symptoms of phosphate deficiency? (8).

Answer 18

Haemoloysis, thrombocytopenia, poor granulocyte function.
Muscle weakness, respiratory failure, rhabdomyolysis.
Metabolic encephalopathy.
Renal dysfunction.

Question 19

Where is the majority go magnesium reabsorbed in the kidney?

Answer 19

Ascending loop of Henle.

Question 20

What is hypomagnesaemia associated with?

Answer 20

Low blood levels of calcium, potassium, phosphate and sodium.

Question 21

How is the bodily distribution of Mg different to calcium and phosphate?

Answer 21

It is found in the intercellular space.

Question 22

Which drugs can cause magnesium depletion? (4).

Answer 22

Antibiotics - gentamicin / carbenicillin.
Chemotherapy - cisplatin.
Diuretics.
FK506 - tacrolimus.

Question 23

What are the effects of magnesium depletion? (5).

Answer 23

Low calcium, phosphate and potassium.
Impaired PTH release and PTH resistance.
Cardiac irritability.
Hyperreflexia, tetany, ataxia and psychosis.
Muscle fibrillation and weakness.

Question 24

How can tissue Mg be ascertained? (4).

Value of each measurement?

Answer 24

Serum - poor correlation. Acute value only.
Erythrocyte - poor.
Leucocyte - good.
Muscle - requires biopsy.