The thyroid gland is one of the largest and major glands amongst the endocrine glands of the human body.

Location and structure:

The thyroid gland is located in the neck below the Adam’s apple (in men).it is placed in the shape of a butterfly in between the cone shaped wings. This gland is covered with a fibrous layer both inside and on the outer surface as well. The parathyroid gland is present posterior to the thyroid glands. The gland is supplied with blood from the arteries branching from the aorta of the heart. The impure blood is carried by the veins.

Thyroid development:

In the embryos, the development of the thyroid gland takes place in the third and the fourth month of gestation and starts to develop from there on, in a few weeks time, the thyroid is connected to the tongue, and the fetus during this stage starts making the TSH linked with the thyroid and thyroxin formation starts during the tenth week.

Features of the thyroid gland:

The following are the main features which are linked with the gland. They are as follows:

I. Follicles:

They are spherical in shape.
They are responsible for absorption of iodine from blood for the formation of the hormone linked with thyroid.
They also contain thyroglobulin, a protein which acts as a reservoir for hormone production and also for the hormones as well.

II. Thyroid epithelial cells:

They surround the follicle.
They secrete the T3 and the T4.
In the inactive state the cell shape is cubical whereas in the active state the shape is columnar with tall cells.

III. Para follicular cells:

They are spread all over in the spaces between follicles.
They secrete the calcitonin.
Functions of the thyroid gland:

The main feature of the thyroid gland is to produce hormones. The important hormones produced by the thyroid gland along with their functions are as follows:

Thyroxin (T4) and triiodothyronin (T3):

It is made by the follicular cells and on the protein tyrosine; a residue from thyroglobulin .the iodine is caught by the “trap” by the hydrogen peroxide which is further made up by the chemical hydrogen peroxide. The T4 is formed when the TSH is stimulated and the absorption of the thyroglobulin. During the formation of TSH the iodinated tyrosine is cleaved whereas in case of the T3, one iodine is absent in comparison to T4, all these are released into the blood. The main target sites for these hormones are the brain cells. They play a major role in maturation of brain.

Calcitonin:

It is responsible for regulating the calcium levels in the body .the Para follicular cells tend to produce in reaction to other components .it is responsible for stimulating motion of calcium inside the bone in contrast to parathyroid hormone. The metabolism of calcium remains as usual after the thyroid removal.

If the levels of thyroid hormones remain normal then the functions of the body move on smoothly but in case there is a variation in the levels of the hormones produced then, it may cause various side effects related to metabolism, digestion etc.