Explain The Thyroid Gland In Biology


Explain The Thyroid Gland In Biology:- Hello friends welcome to yourstudynotes.com friend’s today topic is thyroid gland. I hope this topic is very useful in your study. so let’s start.

Thyroid Gland :-

Thyroid is the largest endocrine gland of the body and weight 25 to 40 gm. This is a “H” shaped bilobed gland situated in the anterior part of the neck at the apex of trachea just below larynx on the ventral side.

Thyroid Gland

The two lateral lobes are connected by a narrow isthmus, which crosses the trachea just below the cricoid cartilage. Thyroid gland is made of numerous spherical cystlike follicles each measuring about 0.02-0.9 mm in diameter. There are more small sized follicles in the thyroid gland of human being. These follicles are suspended in the stroma of connective tissues. Each follicles is surrounded by a very thin basement membrane. Beneath is liea a single layer of glandular cuboidal epithelium. There is great variation in the height of these cuboidal cells.

A jelly like colloid is filled in the cavity of these follicles which is secreted by the epithelium. Scattered in the stroma are groups of some special cells called parafollicular or C cells.

Hormones of thyroid gland:-

Following three hormones are secreted by thyroid gland:-

  1. Triiodothyronine-T3
  2. Tetraiodothyronine- T4
  3. Thyrocalcitonin

Synthesis and chemistry of thyroid hormone:-

The amount of iodine in the blood of adult human being is about 5-6 mg per 100 ml of blood. The thyroid concentrates iodine to the extent of 50 to several thousand times the concentration of this element in the blood plasma. This supported by the fact that after injecting inorganic iodide in blood almost 40 percent of the circulating ions concentrate in thyroid gland within 10 min. Thyroid gland uses about 150µg iodine daily for the secretion of thyroid hormone.

The follicular cell of thyroid gland synthesize a precursor of thyroid hormone thyroglobulin. Thyroglobulin is a 19s glycoprotein made of two polypeptide dimers. Each dimer also contains 10 percent carbohydrate. Each polypeptide dimer contains 115 molecules of amino acid tyrosine.