Thyroxine is secreted by the

The thyroid gland is composed of follicles and stromal tissues. Each thyroid follicle is composed of follicular cells, enclosing a cavity. The follicular cells synthesise two hormones, tetraiodothyronine or thyroxine (T₄) and triiodothyronine (T₃). A few cells called parafollicular cells or C cells lie between follicles produce the hormone thyrocalcitonin (TCT).

Parathyroid glands contain two kinds of epithelial cells. Chief cells or principal cells are more in number and produce parathyroid hormone (PTH), also called parathormone. The function of the second types of cells called oxyphil cells is not yet known.