Blood calcium level is a resultant of how much dietary calcium is absorbed, how much calcium is lost in the urine, how much calcium from blood enters tissues, etc. A number of factors play an important role in these processes. Mark the one which has no role.

The correct option is D Thymosin
The hormone produced by the parathyroid glands is a peptide called parathyroid hormone (PTH). PTH is synthesized and released in response to falling levels of Ca++ in the blood. This cannot be allowed to continue uncorrected because a significant fall in the blood Ca++ level can cause severe muscle spasms. A normal blood Ca++ is important for the functioning of muscles, including the heart, and for the proper functioning of the nervous and endocrine systems. PTH stimulates the osteoclasts (bone cells) in bone to dissolve the calcium phosphate crystals of the bone matrix and release Ca++ into the blood. PTH also stimulates the kidneys to reabsorb Ca++ from the urine and leads to the activation of vitamin D, needed for the absorption of Ca++ from food in the intestine. The thyroid gland also secretes calcitonin (also called thyrocalcitonin), a peptide hormone that plays a role in maintaining proper levels of calcium (Ca++) in the blood. When the blood Ca++ concentration rises too high, calcitonin stimulates the uptake of Ca++ into bones, thus lowering its level in the blood. Thymosin secreted by the thymus plays a role in cell-mediated immunity.