The thyroid or thyroid gland is a part of the endocrine system located at the border between the larynx and trachea, to the base of the anterior portion of the neck. Under the constant control of the pituitary gland, the role of the thyroid gland is to produce and secrete the thyroid hormones, necessary for growth and development of the organism as well as regulation of the metabolism.
What is the thyroid gland?
The thyroid gland is located at the border between the larynx and trachea, to the base of the anterior portion of the neck. Under physiological conditions the gland presents of small size. Its weight is rather variable, but it usually measures between 10 and 50 grams.
The thyroid gland consists of two symmetrical lobes connected at the front by a small isthmus and rest against the rear of the cartilage rings that make up the trachea in a shape that resembles a butterfly. Its position is rather superficial, enabling it to be easily accessible for inspection and palpation. The parathyroid or parathyroid glands are located posteriorly to the thyroid lobes.
The thyroid gland is covered with a fibrous capsule and it is highly vascularized and houses two types of cells: the C cells (or parafollicular) and thyroid follicles. The C cells are those appointed to hormone secretion that regulates calcium levels in the blood, or calcitonin. The thyroid follicles are present in greater numbers: their task is to collect iodine circulating in the blood and turn it into a thyroid prohormone, which is then stored in specific vesicles which are provided.
The thyroid follicles have a spheroidal or ellipsoidal shape, and they are equipped with a central cavity filled with a dense substance called colloid. The colloid is the product of secretion of the elements that make up the wall of the follicles; in its interior there are large amounts of thyroglobulin, a protein that is the storage form of the main components of the thyroid hormones, T3 (triiodothyronine) and T4 (tetraiodiotironina or thyroxin).
When it is necessary, the colloid substance is fragmented from the metabolic activity of the follicular cells (through the intervention of a specific enzyme) to obtain the triiodothyronine (for an approximately 20%) and the tetraiodiotironina (80%), that are entered into the blood in the large network that irrigates the gland. The cells constituting the thyroid follicles are called thyrocytes.
What function does the thyroid gland serve?
The thyroid gland, which acts under the control of the pituitary gland, is responsible for the production and secretion of thyroid hormones, necessary for growth and development of the organism.
Moreover, the thyroid gland produces and stores hormones that help regulate blood pressure, body temperature, heart rate and the rate at which food is converted into energy. Additionally, the thyroid hormones regulate the rate of chemical reactions in the body (the metabolism) as well as growth and development. It can be said that the thyroid hormones are essential for the proper function of every cell in the body.
