Calcium homeostasis Flashcards
What cells produce PTH?
Chief cells of the parathyroid gland.
What organs are involved in calcium homeostasis?
Bones.
GIT.
Kidneys.
What is PTH released in response to?
Low serum calcium.
What are the functions of PTH?
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.
What are the functions of calcitrol?
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.
Where is calcitonin synthesised?
Parafollicular cells of the thyroid.
What are the functions of calcitonin?
Inhibits bone resorption by osteoclasts.
Name two ways in which calcium enters the blood?
Intestinal absorption.
Bone resorption.
Name two ways in which calcium is removed from the blood?
Renal excretion.
Bone absorption.
What are the hormonal causes of hypercalcaemia?
Primary hyperparathyroidism.
Hypervitaminosis D.
Malignant hypercalcaemia.
What are the non-hormonal cause of hypercalcaemia?
Renal failure. Milk alkali syndrome. Familial benign hypocalciuric-hypercalcaemia - decreased sensitivity to calcium > increased calcium needed to suppress PTH. Sarcoidosis. Granulomatous diseases.
What drugs can cause hypercalcaemia?
Thiazide diuretics.
Lithium.
What effect does hypercalcaemia have on Na+ channels?
Blocks Na+ channels > decreased activity.
What are the signs & symptoms of hypercalcaemia?
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.
What are the main causes of hypocalcaemia?
Hypoparathyroidism. Pseudohypoparathyroidism. Hypovitaminosis D. > rickets. > osteomalacia. > decreased renal production. Hypomagnaesaemia. Malabsorption from the GIT. Increased dietary phosphate. Low dietary calcium.