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1. How large are the parathyroid glands?
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Correct answer:
They are about the size of split peas.
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2. Where are the parathyroid glands usually situated?
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Correct answer:
They usually lie in two pairs behind the lateral lobes of the thyroid gland.
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3. Where are the inferior parathyroid glands situated?
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Correct answer:
The inferior parathyroid glands may lie almost anywhere in the neck or superior mediastinum although the majority lie within 1 cm of the lower thyroid pole.
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4. What substance is produced by the parathyroid glands??
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Correct answer:
Parathormone.
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5. What are the effects of parathormone?
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(1) It increases the excretion of phosphate from the kidney by inhibiting its tubular reabsorption (phosphaturic effect); tubular reabsorption of calcium is reciprocally increased.
(2) It stimulates osteoclastic activity in the bones, resulting in the decalcification and liberation of excessive amounts of calcium and phosphorus in the blood.
(3) It activates the 1α-hydroxylase enzyme in the kidney, which converts the inactive 25-hydroxycholecalciferol (25-hydroxy-vitamin D) into 1,25-dihydroxycholecalciferol. The resultant activated 1,25 form of vitamin D facilitates intestinal absorption of calcium.
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6. What is the phosphaturic effect?
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Correct answer:
This is the effect of parathormone on the kidney. Parathormone reduces tubular reabsorption of phosphate from the kidney and reciprocally increases the reabsorption of calcium.
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7. What is the effect of parathormone on the bones?
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Correct answer:
It stimulates osteoclastic activity in the bones, resulting in decalcification and liberation of excessive amounts of calcium and phosphorus in the blood.
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8. What are the effects of increased parathormone production?
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Correct answer:
(1) A raised serum calcium and a lowered serum phosphate, as these substances are related reciprocally. (2) An increased excretion of phosphate in the urine (phosphaturic effect of parathormone). (3) An increased excretion of calcium in the urine. The large amount of calcium filtered (owing to hypercalcaemia) exceeds the tubules’ capacity to resorb it all, so increased calcium excretion occurs. (4) Increased osteoclastic activity, with a raised serum alkaline phosphatase associated with decalcification of the bones.
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9. Which substance is produced by active osteoclasts?
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Correct answer:
Alkaline phosphatase.
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10. Why is there increased excretion of calcium in the case of hyperparathyroidism?
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Correct answer:
Even though calcium reabsorption by the kidney tubule is increased in hyperparathyroidism, the increased filtration due to raised plasma levels, as a result of increased osteoclasis, causes a net loss of calcium in the urine.
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11. What happens when there is a lack of parathormone? What are the clinical features?
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Correct answer:
Lack of parathormone results in a low serum calcium and hyperirritability of skeletal muscle with carpopedal spasms, the syndrome being called tetany. Spasms may affect any part of the body, but typically the hands and feet. The wrists flex and the fingers are drawn together in extension, the so-called ‘main d’accoucher’. This spasm may be induced by placing a tourniquet around the arm for a few minutes (Trousseau’s sign). Hyperirritability of the facial muscles may be demonstrated by tapping over the facial nerve, which results in spasm (Chvostek’s sign).
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12. What is the most common cause of hypoparathyroidism?
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Correct answer:
Removal or bruising of the parathyroids during thyroidectomy.
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13. What is ‘main d’accoucher’?
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Correct answer:
This is the carpopedal spasm which occurs as a result of hypocalcaemia. The wrists flex and the fingers are drawn together in extension.
