The thyroid gland consists of two lobes; it is the largest (weighs about 25 grams) adult endocrine gland. The isthmus connects the two lobes of the thyroid gland. The thyroid is located at the neck, adjacent to the trachea, and beneath the larynx. It appears in a butterfly shape and is covered around the trachea. It is composed of thyroid follicles that are covered by follicular cells. The follicular cells secret thyroid hormones (TH) such as triiodothyronine (T 3 ) and thyroxine (T 4 ). The thyroid gland releases TH into the bloodstream. Thyroid hormones act by binding to their thyroid hormone receptors (TR), which is a superfamily of nuclear receptors. TR encoding genes are classified into α (TRα) and β (TRβ). Thyroid stimulating hormone (TSH) regulates hormones’ (T 3 and T 4 ) secretion from the thyroid. TH raises the metabolic rate by promoting the adequate supply of blood and oxygen. Also, TH increases the heart rate and respiratory rate, and is involved in the breakdown of carbohydrates and fats to provide energy. TH regulates appetite, alertness, the secretion of the growth hormone, body growth, reproduction, and the circulatory system. Abnormal secretion of thyroid hormones may cause thyroid problems.

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Chapter 17.7, Problem 29BYGO

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The thyroid gland consists of two lobes; it is the largest (weighs about 25 grams) adult endocrine gland. The isthmus connects the two lobes of the thyroid gland. The thyroid is located at the neck, adjacent to the trachea, and beneath the larynx. It appears in a butterfly shape and is covered around the trachea. It is composed of thyroid follicles that are covered by follicular cells. The follicular cells secret thyroid hormones (TH) such as triiodothyronine (T₃) and thyroxine (T₄). The thyroid gland releases TH into the bloodstream. Thyroid hormones act by binding to their thyroid hormone receptors (TR), which is a superfamily of nuclear receptors. TR encoding genes are classified into α (TRα) and β (TRβ). Thyroid stimulating hormone (TSH) regulates hormones’ (T₃ and T₄) secretion from the thyroid. TH raises the metabolic rate by promoting the adequate supply of blood and oxygen. Also, TH increases the heart rate and respiratory rate, and is involved in the breakdown of carbohydrates and fats to provide energy. TH regulates appetite, alertness, the secretion of the growth hormone, body growth, reproduction, and the circulatory system. Abnormal secretion of thyroid hormones may cause thyroid problems.

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