What Does the Thyroid do?


The thyroid gland is considered to be one among the largest endocrine glands in the body. The thyroid is a butterfly shaped gland that lies above the collar bone beneath the neck cartilage. The thyroid gland is located below the thyroid cartilage at the laryngeal prominence (Adam’s apple) in front of the neck. The gland contains two poles, upper and lower; two lobes, right and left; that are joined by the isthmus at the center of the thyroid, which is situated below the cricoid cartilage.The main function of the thyroid gland is to stimulate the rate of metabolism in the body. The parafollicular cells of the thyroid gland secrete a hormone called calcitonin, which combines together with the parathyroid hormone secreted by the parathyroid gland ( located in 2 pairs above the thyroid gland), to regulate the calcium homeostasis in the body.

Here is a brief outline about what is thyroid gland, its anatomy, functions and its effect on body metabolism:

Anatomy of the thyroid gland                              

The thyroid gland is located below the larynx (voice box), in front of the neck. It is a small, butterfly shaped gland of two inches, which consists of two lobes, which are connected together at the center by the tissue called isthmus and the two poles are located on either side of the trachea (windpipe). The tissue of the thyroid gland consists of two types of cells named as parafollicular cells and follicular cells. Follicular cells make up the majority of the thyroid tissue and their principal function is to secrete thyroxine (T4) and triiodothyronine (T3) hormones that contain iodine. The calcitonin hormone is secreted by the parafollicular cells (c-cells) of the thyroid gland. These hormones contain iodine and hence the thyroid gland requires iodine to synthesize sufficient level of these hormones.

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Thyroid gland Functions

The main function of the thyroid gland is to rapidly control the expenditure of energy in the body, synthesize proteins, and regulate the body response to other hormones. It produces thyroid hormones before taking part in these functions. The two principal thyroid hormones secreted by the thyroid gland include triiodothyronine (T3) and thyroxine, also called as tetraiodothyronine (T4). These hormones mainly regulate the growth and development of the body; rate of metabolism; and functioning mechanism of various systems in the body. Iodine and tyrosine synthesize both T3 and T4 hormones. In addition to that, the thyroid gland also synthesizes calcitonin that is important for calcium homeostasis in the system.

The thyroid-stimulating hormone (TSH), which is produced by the anterior part of pituitary gland, regulates the hormonal output of thyroid gland. The hypothalamus produces the thyrotropin-releasing hormone (TRH), which in turn regulates the TSH. Any imbalance or functional irregularity of these glands could lead to thyroid conditions. Some of the most common disorders of thyroid gland include hypothyroidism, which is due to an under active thyroid gland that secretes insufficient thyroid hormones; and hyperthyroidism, caused by an overactive thyroid gland by secreting overtly high level of hormones. Some of the important functions that are carried out by the thyroid gland in the body are as follows:

  • The thyroid gland is considered as an endocrine gland that secretes sufficient level of thyroid hormones to regulate the metabolism in the body.

  • Generally, metabolism is the rate at which the system exerts energy to perform normal functions throughout the body, including the rate of tissue regeneration process, and growth pacing.

  • Thyroid hormones also regulate the rate at which oxygen is delivered and utilized by the body tissues

  • It promotes and enhances the synthesis of protein throughout the body.

  • The rate of metabolism in the body is based on the body requirements at any period of time during certain conditions ranging from a baseline level at rest, boosting up the metabolic rate during physical activity, and in body response to various health conditions such as fever, or infection or illness.

  • The major role played by the thyroid gland is to maintain the calcium balance and metabolic rate in the body.

  • It secretes the two hormones T4 and T3,which stimulate the production of protein in every tissue in the body.

  • The calcitonin hormone combines with the parathyroid hormone (secreted by the parathyroid gland) to maintain calcium homeostasis (regulation of calcium levels) in the body.

  • The pituitary gland controls the thyroid hormone levels in the body by the secretion of thyroid-stimulating hormone (TSH), which functions under the control of the hypothalamus.

  • The calcitonin hormone, secreted by the parafollicular cells of thyroid reduces the circulating calcium levels in the blood.

Dysfunctional thyroid gland

  • Alteration in metabolic rate can affect the normal cardiac output, pulse rate, heat production and respiratory rate.

  • An overactive thyroid gland abnormally increases the thyroid hormone production in the body, the condition referred to as thyrotoxicosis or hyperthyroidism.

  • An under active thyroid gland produces abnormally low levels of thyroid hormones that are not sufficient enough to perform any important function and meet the body needs, the condition referred to as myxoedema or hypothyroidism.

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