Calcium homeostasis

Question 1

What cells produce PTH?

Answer 1

Chief cells of the parathyroid gland.

Question 2

What organs are involved in calcium homeostasis?

Answer 2

Bones.
GIT.
Kidneys.

Question 3

What is PTH released in response to?

Answer 3

Low serum calcium.

Question 4

What are the functions of PTH?

Answer 4

Stimulates bone resorption of calcium & phosphate.
Stimulates renal tubular re-absorption of calcium.
Stimulates renal excretion of phosphate.
Activates renal 1a hydroxylase > activation of vitamin D3.

Question 5

What are the functions of calcitrol?

Answer 5

Stimulates the absorption of calcium & phosphate from the SI.
Stimulates the differentiation of osteoclasts > resorption of calcium/phosphate from bone.
Inhibits the transcription of the PTH gene - negative feedback.

Question 6

Where is calcitonin synthesised?

Answer 6

Parafollicular cells of the thyroid.

Question 7

What are the functions of calcitonin?

Answer 7

Inhibits bone resorption by osteoclasts.

Question 8

Name two ways in which calcium enters the blood?

Answer 8

Intestinal absorption.

Bone resorption.

Question 9

Name two ways in which calcium is removed from the blood?

Answer 9

Renal excretion.

Bone absorption.

Question 10

What are the hormonal causes of hypercalcaemia?

Answer 10

Primary hyperparathyroidism.
Hypervitaminosis D.
Malignant hypercalcaemia.

Question 11

What are the non-hormonal cause of hypercalcaemia?

Answer 11

Renal failure.
Milk alkali syndrome.
Familial benign hypocalciuric-hypercalcaemia - decreased sensitivity to calcium > increased calcium needed to suppress PTH.
Sarcoidosis.
Granulomatous diseases.

Question 12

What drugs can cause hypercalcaemia?

Answer 12

Thiazide diuretics.

Lithium.

Question 13

What effect does hypercalcaemia have on Na+ channels?

Answer 13

Blocks Na+ channels > decreased activity.

Question 14

What are the signs & symptoms of hypercalcaemia?

Answer 14

CNS:
> decreased alertness.
> confusion.
> coma.

GIT:
> constipation.
> N & V.
> Anorexia.

Renal:
> polyuria.
> dehydration.
> increased risk of kidney stones.

Skeletal:
> Increased fracture risk - due to resorption.

CV:
> hypertension.
> Shortened QT interval.

Question 15

What are the main causes of hypocalcaemia?

Answer 15

Hypoparathyroidism.
Pseudohypoparathyroidism.
Hypovitaminosis D.
> rickets.
> osteomalacia.
> decreased renal production.
Hypomagnaesaemia.
Malabsorption from the GIT.
Increased dietary phosphate.
Low dietary calcium.

Question 16

What effect does hypocalcaemia have on Na+ channels?

Answer 16

Lowers threshold for depolarisation > increased activity.

Question 17

What are the signs & symptoms of hypocalcaemia?

Answer 17

Chovsteks sign - facial nerve hyperexcitability.
Trousseau sign - occlusion of the brachial artery.
Paraesthesia.
Tetany.
Muscle spasms.
Hyper-reflexia.
Grand mal fits.
Cataracts.

GIT:
> Diarrhoea.

CV:
> Prolonged QT.