There are two important thyroid hormones that regulate growth, metabolism, and reproduction. The thyroid gland takes iodide from the blood and converts it into thyroxine. Thyroxine is known as T4 because it has four iodide ions. Thyroxine is stored in the thyroid gland and released into the blood as needed. Thyroxine can be converted into the active form of thyroid hormone called triiodothyronine.
Triiodothyronine is also known as T3 because it has three iodide ions. This conversion of thyroxine to the active form, T3, takes place in tissues such as the liver and the brain and requires selenium. The action of T3 is based upon its capability of causing the synthesis of specific proteins in the nucleus of the cell.
Thyroid Hormones with Iodide
Thyroxine The storage and transport thyroid hormone known as T4
Triiodothyronine The active thyroid hormone known as T3
There are several steps in the regulation of the thyroid hormones. Deep in the brain is the hypothalamus. When thyroid hormones are needed, the hypothalamus secretes a hormone (thyrotropin-releasing hormone) that targets the pituitary gland. In response, the pituitary gland secretes thyroid-stimulating hormone (TSH), as seen in Figure 13-1. This thyroid-stimulating hormone tells the thyroid gland to take more iodide from the blood. The thyroid-stimulating hormone also stimulates the thyroid gland to produce and release more thyroxine and small amounts of the active thyroid hormone T3.
When levels of thyroxine are adequate, the pituitary gland secretes less of the thyroid-stimulating hormone. When levels of thyroxine start falling, the pituitary gland secretes more of the thyroid-stimulating hormone. Iodine deficiency causes lowered levels of thyroxine in the blood. In response, the pituitary gland releases more thyroid-stimulating hormone. Over time, this can
Figure 13-1 Control of thyroid hormones.
lead to enlargement of the thyroid gland, located in the neck. This enlargement of the thyroid gland is called goiter and can result in a swelling in the thyroid gland in the neck.
More about Iodine:
Wow, I never knew the power of natural supplements until I tried desiccated porcine thyroid tablets . This knowledge has brought me back to my real life and in good condition weight. I have decreased 15 pounds and am now enjoying life better than before.