Calcium homeostasis Flashcards

1
Q

What cells produce PTH?

A

Chief cells of the parathyroid gland.

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2
Q

What organs are involved in calcium homeostasis?

A

Bones.
GIT.
Kidneys.

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3
Q

What is PTH released in response to?

A

Low serum calcium.

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4
Q

What are the functions of PTH?

A

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.

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5
Q

What are the functions of calcitrol?

A

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.

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6
Q

Where is calcitonin synthesised?

A

Parafollicular cells of the thyroid.

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7
Q

What are the functions of calcitonin?

A

Inhibits bone resorption by osteoclasts.

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8
Q

Name two ways in which calcium enters the blood?

A

Intestinal absorption.

Bone resorption.

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9
Q

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

A

Renal excretion.

Bone absorption.

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10
Q

What are the hormonal causes of hypercalcaemia?

A

Primary hyperparathyroidism.
Hypervitaminosis D.
Malignant hypercalcaemia.

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11
Q

What are the non-hormonal cause of hypercalcaemia?

A
Renal failure.
Milk alkali syndrome.
Familial benign hypocalciuric-hypercalcaemia - decreased sensitivity to calcium > increased calcium needed to suppress PTH.
Sarcoidosis.
Granulomatous diseases.
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12
Q

What drugs can cause hypercalcaemia?

A

Thiazide diuretics.

Lithium.

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13
Q

What effect does hypercalcaemia have on Na+ channels?

A

Blocks Na+ channels > decreased activity.

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14
Q

What are the signs & symptoms of hypercalcaemia?

A

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.

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15
Q

What are the main causes of hypocalcaemia?

A
Hypoparathyroidism.
Pseudohypoparathyroidism.
Hypovitaminosis D.
> rickets.
> osteomalacia.
> decreased renal production.
Hypomagnaesaemia.
Malabsorption from the GIT.
Increased dietary phosphate.
Low dietary calcium.
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16
Q

What effect does hypocalcaemia have on Na+ channels?

A

Lowers threshold for depolarisation > increased activity.

17
Q

What are the signs & symptoms of hypocalcaemia?

A
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.