Question

Assertion : Hormone calcitonin has an antagonistic effect to that of parathormone.

Reason : Calcitonin decreases blood calcium level while parathormone levels increase blood calcium level.

• A. Both assertion and reason are true but reason is not the correct explanation of the assertion.
• B. Assertion is true but reason is false.
• C. Both assertion and reason are false.
• D. Both assertion and reason are true and the reason is the correct explanation of the assertion.

Answer 1

The correct option is D Both assertion and reason are true and the reason is the correct explanation of the assertion.

In addition to triiodothyronine and tetraiodothyronine, thyroid gland secrete an additional protein hormone calcitonin or thyrocalcitonin. This hormone is secreted by parafollicular cells of thyroid stroma. It retards the dissolution of the bone and stimulates the excretion of calcium in urine. Thereby, it lowers calcium levels in extracellular fluid (ECF).

The parathyroid gland which is located at the backside of the thyroid gland secrete a peptide hormone called parathormone. Parathormone, also known as Collip’s hormone, is secreted by chief cells of the parathyroid gland. It maintains the blood calcium level by increasing its absorption from food in the intestine and its reabsorption from nephrons in the kidney. The maintenance of a balanced calcium level is a combined function of parathormone and calcitonin. When calcium level falls below normal, the parathormone maintains it by promoting its absorption, reabsorption and also by demineralisation of bones.

When blood calcium level exceeds above normal, then calcitonin hormone increases excretion of calcium in urine.