Assertion: Hormone calcitonin has antagonistic effect to that of parathormone.
Reason: Calcitonin decreases blood calcium level while parathormone increases blood calcium level.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false.

Answer

A

Explanation

Calcitonin or thyrocalcitonin is secreted by parafollicular cells of thyroid stroma. It retards bone dissolution and stimulates excretion of calcium in urine. Thus, it lowers calcium level in extra cellular fluid (ECF). Parathormone is secreted by chief cells of parathyróid gland and is also known as Collip's hormone. It maintains blood calcium level by increasing its absorption from food in intestine and its reabsorption from nepłrons in the kidney. Maintenance of proper calcium level is in fact, a combined function of parathormone and calcitonin. When calcium level falls below normal then parathormone maintains it by promoting its absorption, reabsorption and also by demineralization of bones. When blood calcium level exceeds above normal then proper calcitonin hormone increases excretion of calcium in urine.