What is the role of the thyroid gland in the endocrine system?

The thyroid gland is one of the important organs of the endocrine system. The thyroid gland is an endocrine gland in the neck consisting of two connected lobes. The lower two-thirds of the lobes are connected by a thin band of tissue called the thyroid gland. The thyroid is located in the front of the neck, below the Adam's apple.
Microscopically, the functional unit of the thyroid gland is the globular thyroid follicle, lined with follicular cells (thyroid cells) and parafollicular cells surrounding a duct that contains a colloid.

The thyroid gland in the endocrine system secretes three hormones including two thyroid hormones (triiodothyronine-T3 and thyroxine-T4) and a peptide hormone (calcitonin). Thyroid hormones affect metabolic rate, protein synthesis, growth and development. Calcitonin plays a role in calcium homeostasis.
Two thyroid hormones (T3, T4) are regulated by thyroid-stimulating hormone (TSH) and are secreted from the anterior pituitary. Thyroid (TSH) is regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus.
The thyroid gland develops in the floor of the pharynx at the base of the tongue at 3-4 weeks of gestation. It then descends anteriorly to the pharynx, and finally to the base of the neck within a few weeks. During migration, the thyroid gland remains connected to the tongue by a narrow tube (thyroid duct). At the end of the fifth week of pregnancy, the thyroid ducts degenerate. And two weeks later, the detached thyroid moves to its final location.
Thyroid disorders include hyperthyroidism, hypothyroidism, thyroiditis (inflammation of the thyroid gland), thyroid enlargement (goiter), thyroid nodules, and thyroid cancer. Hyperthyroidism is characterized by excessive secretion of thyroid hormone. The most common cause is an autoimmune disorder, Graves' disease.
Hypothyroidism is characterized by a deficiency of thyroid hormone. A common cause is iodine deficiency. In iodine-deficient regions, hypothyroidism secondary to iodine deficiency is the leading cause of intellectual disability. In areas where there is enough iodine, a common cause of hypothyroidism is the autoimmune disorder thyroiditis.

2.1. Thyroid hormone The main function of the thyroid gland is to produce iodine-containing thyroid hormones (triiodothyronine-T3 and thyroxine-T4 and the peptide hormone calcitonin). Thyroid hormones are made from iodine and tyrosine. Triiodothyronine (T3) is so named because it contains three iodine atoms per molecule, and thyroxine (T4) contains four iodine atoms per molecule. Thyroid hormones have effects on the body such as:
Metabolism: Thyroid hormones increase the basal metabolic rate and have effects on most body tissues. Appetite, absorption, and bowel movements are all affected by thyroid hormones. They increase absorption in the intestines, absorption by cells and breakdown of glucose. They stimulate fat breakdown and increase the number of free fatty acids. Although, increasing free fatty acids, thyroid hormone lowers cholesterol levels. And perhaps this is how to speed up the excretion of cholesterol in the bile. Cardiovascular: Thyroid hormones increase the rate of heart rate. They increase breathing rate, oxygen consumption, and mitochondrial activity. Combined, these factors increase blood flow and body temperature Growth: Thyroid hormones are important for normal growth. They speed up maturation and the cells of the developing brain are the primary targets of the thyroid hormones T3 and T4. Thyroid hormone plays a particularly important role in brain maturation during fetal development and in the first years of life. Thyroid hormones also play a role in maintaining sexual function, sleep, and thinking. Increased levels are associated with increased thought speed but decreased concentration. Sexual function includes libido and maintenance of a normal menstrual cycle.

2.2. Hormone production Thyroid hormones are made from thyroglobulin. This is a protein in the colloidal lumen of the follicle that is initially produced in the rough endoplasmic reticulum of the follicular cell and then transported into the follicular lumen. Thyroglobulin contains 123 tyrosine units that react with iodine in the lumen of the follicle.
When follicular cells are stimulated by thyroid-stimulating hormone, follicular cells reabsorb thyroglobulin from the follicular lumen. The iodine tyrosine is cleaved to form the thyroid hormones T3, T4, DIT, MIT.
2.3. Regulation The production of thyroxine is mainly regulated by thyroid-stimulating hormone (TSH). TSH release is in turn stimulated by thyrotropin-releasing hormone (TRH), and is readily released from the hypothalamus.
Thyroid hormones provide negative feedback to the thyroid gland TSH and TRH: when thyroid hormone is elevated, TSH production is suppressed. Conversely, this negative feedback also occurs when TSH is high, causing TRH production to be suppressed.
TRH is secreted in increased concentrations in situations such as cold exposure to stimulate thermogenesis. In addition to being inhibited by the presence of thyroid hormone, TSH production is attenuated by dopamine somatostatin and glucocorticoids.
2.4. Calcitonin The thyroid gland also produces the hormone calcitonin, which helps regulate calcium levels in the blood. Parafollicular cells produce calcitonin in response to high blood calcium. Calcitonin reduces the release of calcium from bone, by reducing the activity of osteoclasts, the bone cells that break down bone. Bone is continuously reabsorbed by osteoblasts and produced by osteoblasts. Therefore, calcitonin effectively stimulates the movement of calcium into the bone.
The effects of calcitonin are opposite to those of parathyroid hormone (PTH) produced in the parathyroid glands. However, calcitonin appears to be less essential than PTH because calcium metabolism remains clinically normal after thyroidectomy but not parathyroid gland. The thyroid gland plays an important role in the endocrine system and the human body. Therefore, as soon as the body shows signs of thyroid-related diseases, you need to see a doctor soon for advice and treatment. To register for examination and treatment at Vinmec International General Hospital, you can contact Vinmec Health System nationwide, or register online HERE
Reference source: Ncbi.nlm.nih. gov
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