Question

Choose the correct answer from the alternatives given.
Which of the following is not involved in calcium metabolism?

• A. Calmodulin
• B. Calcitonin
• C. Parathyroid hormone
• D. Atrial natriuretic factor

Answer 1

The correct option is D Atrial natriuretic factor

(A)Calmodulin is a multifunctional intermediate calcium binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the binding of Ca2+ is required for the activation of calmodulin.

(B) Calcitonin is a hypocalcemic hormone. This is secreted by the C-cells in the thyroid gland. It acts on bone and the kidney to reduce the blood calcium level. It reduces the reabsorption of calcium from bones and inhibits reabsorption of calcium by the renal tubules.

(C) The parathyroid gland secretes a peptide hormone called parathyroid hormone (PTH). The secretion of PTH is regulated by the circulating levels of calcium ions. PTH increases the calcium levels in the blood. PTH also stimulates reabsorption of calcium by the renal tubules and increase calcium absorption from the digested food.

(D) Atrial Natriuretic Factor (ANF) is released when there is an increase in blood flow to the atria of the heart. ANF can cause vasodilation (dilation of blood vessels) and thereby decrease the blood pressure. ANF mechanism, therefore, acts as a check on the renin-angiotensin mechanism.

So the correct answer is the Atrial Natriuretic Factor.