Final answer:
The thyroid gland secretes two main hormones, thyroxine (T4) and triiodothyronine (T3), which are crucial in regulating the body's metabolism. It also produces calcitonin, which helps regulate blood calcium levels.
Step-by-step explanation:
The thyroid can affect most cells and metabolism; it secretes two main hormones: thyroxine (T4) and triiodothyronine (T3). These hormones are synthesized from the amino acid tyrosine in the presence of iodine. In the thyroid gland, iodide from the plasma is taken up actively and transformed into active iodine (I or I+) by the enzyme thyroperoxidase, which requires hydrogen peroxide for this process.
The secretion of T3 and T4 is stimulated by thyroid-stimulating hormone (TSH) from the anterior pituitary gland. Once released, these hormones travel to cells throughout the body, where they increase metabolism by increasing energy use and the rate of metabolism. Also, the thyroid produces calcitonin, a hormone that helps regulate blood calcium levels by stimulating the movement of calcium into the bones.