Name a hormone secreted by the thyroid gland that acts to lower blood calcium

Thyrocalcitonin or TCT

Explanation:

Thyrocalcitonin or TCT is a non-iodinated calcium lowering hormone. It is originating from the parafollicular cells or C cells (C for calcium).

The thyroid gland consists of follicles of cuboidal epithelial cells. These cuboidal cells have a nucleus at the base. These are principal cells responsible for the synthesis of thyroid hormones.

In between these follicular cells, other high cuboidal cells are present, known as parafollicular cells / C cells. These cells synthesise the hormone TCT. When there is high levels of calcium ions in the serum, TCT will release. This lowers the high level of calcium ions in the blood and plasma to normal level. This is done due to the deposition of calcium in the bone.