Where is the thyroid gland located and how important is it for the body?
It is a butterfly-shaped endocrine gland; each side is about the size of a thumb. It lies on the neck before the windpipe, below the larynx and has grown together with the thyroid cartilage through the fetal posterior capsule. On both sides, it borders the neck vessels, behind the thyroid sit the epithelial bodies or parathyroid glands (which produce the parathyroid hormone which is important for calcium metabolism); the nerves of the vocal chords also run on both sides behind the thyroid gland (Nervus laryngeus recurrent).
The hormones of the thyroid gland control various functions of the body, such as cell metabolism (heat and protein production), nerve function and heartbeat.
The thyroid gland is controlled by the brain; through hypothalamic hormones and in particular the pituitary gland. The thyroid gland produces the hormones triiodothyronine (T3, with three iodine atoms) and thyroxine (T4, with four iodine atoms), which are essential for the metabolism, hence the thyroid gland is dependent on the regular intake of iodine with food for its hormone production.
When T3 (about 20% of all thyroid hormones in the blood and 80% within the cells) and T4 (about 80% of all thyroid hormones in the blood and 20% within the cells) are not present in the blood in sufficient quantity, the pituitary hormone which stimulates the thyroid (TSH = Thyroid Stimulating Hormone) is released and the production rate of thyroid hormones is increased and vice versa (feedback mechanism).
If the amount of thyroid hormone present in the blood is too little (hypofunction) or too much (hyperfunction), then the TSH level in blood is correspondingly increased or decreased.
