Thyroid gland develops from the endoderm of the embryo. The thyroid gland is the largest endocrine gland of the human body which is located on the ventral side of the neck just below the larynx. Thyroid gland surrounds the front of the larynx and upper part of the trachea in the neck. Thyroid has two lobes on either side of the trachea.
Structure of thyroid gland
The thyroid gland is a pink coloured, H-shaped, bi-lobed and largest gland of the human body. The lobes of the thyroid gland are connected by an isthmus. In normal healthy person, the weight of thyroid gland is about 25 gm. The thyroid gland is larger in female than in male. The thyroid is profusely supplied with blood vessels. The gland consists of a large number of small closed follicles or acini of about 200 mili-micron in diameter. Each follicle is lined by a secretory epithelium of cuboidal or low columnar type. These follicles are held together by areolar tissue. Each follicle contains a clear viscid proteinaceous amber coloured colloid which normally comprises the greater part of the thyroid mass. The colloid consists mainly of iodinated thyroglobulin. In poly breeders like human beings the gland functions almost uniformly but in seasonal breeders, the gland is active at one stage and inactive at the other.
Hormones of thyroid gland
Thyroid gland secretes following hormones:
Thyroxine and tri-iodothyronine
Both of these hormones are iodine containing forms of amino acid tyrosine. They are stored in the colloids that fill the follicle and are released into the blood when required. Chemically thyroxine is tetra iodothyronine and also found as tri-iodothyronine. T 3 is more active (3 to 4 times) than T4. Both are iodine containing amine hormones. T 3 has 10% iodine while T 4 has 65% iodine. Thyroxine hormone was isolated by Kochar (1916) and it is crystalized by Kendall (1919). On reaching tissue 50% of T4 get converted into T3. Both of these hormones are secreted by follicular cells of thyroid gland.
Functions of thyroxin hormone
The functions of thyroxine hormone are as follows :
Thyrocalcitonin (TCT) hormone is secreted by the parafollicular cells (='C' cells) present in the stroma of the thyroid gland. Thyrocalcitonin is a protein composed of thirty-two amino acids. Thyrocalcitonin is a hypocalcemic, hypophosphatemic hormone. Thyrocalcitonin was discovered by H. H. Corp in 1962.
Functions of thyrocalcitonin
The functions of thyrocalcitonin hormones are:
Hyposecretion of thyroid
The hyposecretion of thyroid causing the following diseases:
Hypersecretion of thyroid
The hypersecretion of thyroid gland causing the following diseases:
Hakimuddin Kuwakhedawala is based in India with over 15 years experience as a teacher. Teaching and writing are his passion. Most of the articles of Hakimuddin are related to education, exam, environmental problems, etc.
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A nice summary of thyroid gland and its role in humans. The thyroid hormones are important for day to day metabolic functions of the body and hence often during times of increased demand ( puberty,pregnancy) the gland enlarges and hypo hypothyroidism can develop. Since iodine is crucial to the production of the thyroid hormones, widespread use of iodized salt has led to a decrease in thyroid disease(goiters). In current obstetric practice,it has become a must to monitor the thyroid hormone levels to ensure the health of the mother and the growing baby inside her.
Many of the diseases of thyroid (hypo function and hyper function) can be managed with tablets. Surgery is needed for complex cases of hyper function, for large goiters and when there is a diagnosis of cancer. When in doubt, see your local family physician or an endocrinologist.