The Thyroid Gland Function
The thyroid gland is an integral part of the human endocrine system. It is a butterfly-shaped organ located in the neck, lying just below the thyroid cartilage of the larynx (the “Adam’s apple”). The thyroid releases the thyroid hormones T3 and T4 (thyroxines), which perform a number of roles in the body, including:
- Growth
- Increases in metabolism for energy
- Increased heat production
- Development and maintenance of the nervous system
Different cells in the thyroid gland produce another hormone, called calcitonin. When the amount of calcium in the blood increases, calcitonin is released. Calcitonin acts on cells in the bone called osteoblasts, which take up the calcium and deposit it to form new bone. Calcitonin also inhibits another group of cells in the bone, which are called osteoclasts. Osteoclasts break down bone and cause release of calcium into the bloodstream.
Release of thyroid hormone from the thyroid gland is controlled by the hypothalamus and the anterior pituitary gland. When the body is subject to stressors, such as extreme cold, the hypothalamus is stimulated, causing release of thyrotropin releasing hormone (TRH). TRH travels to the anterior pituitary in a separate bloodstream, causing the anterior pituitary to release thyroid-stimulating hormone (TSH). TSH is secreted into the bloodstream and travels to the thyroid gland, where it promotes production and release of T3 and T4. Once released, T3 and T4 enter the systemic bloodstream and act on many cells in the body to increase metabolism, increase temperature and promote growth and development. As with most hormone systems, elevated levels of T3 and T4 in the blood exert negative feedback onto the hypothalamus and pituitary. This limits additional release of TRH and TSH to maintain a balance of hormone levels in the bloodstream.
Iodine and thyroid function
Adequate dietary iodine is imperative for the function of the thyroid gland. Iodine is a component of T3 and T4, and thus, is necessary for synthesis of the key thyroid hormones. Iodine deficiency is a common cause of hypothyroidism, a condition where the thyroid is producing insufficient hormones. Iodine is rich in seafood, and to an extent plants; depending on the iodine concentration of the soil. Iodine is added to common table salt to reduce the impact of iodine deficiency. Iodine is also a particularly important mineral in pregnancy, due to the importance of thyroid hormones on the growth and development of the foetus. Thyroid hormones are especially important for the development of the nervous system; maternal iodine deficiency in pregnancy may cause cretinism in the child.
In summary
The thyroid gland regulates many metabolic processes, including growth and energy expenditure. Around one in 20 people will experience some form of thyroid dysfunction in their lifetime. Common problems include overactivity and underactivity of the thyroid gland. Most thyroid conditions are caused by autoimmunity. These conditions have a genetic link. People with a family history of thyroid conditions have a higher risk of also having a thyroid condition and other autoimmune conditions.
If you have questions or concerns about thyroid problems see your local doctor who will arrange for you to see a thyroid surgeon.
