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What Does the Thyroid Do?

What is thyroid

Endocrine gland is made up of many glands and thyroid gland is a part it. It produces stores and releases hormones into the blood. The thyroid gland is butterfly shaped and is about 2 inches long. It is located in front of the throat below the Adam’s Apple. It is made of two lobules. On either sides of the windpipe these lobules lie and are connected by isthmus.

Hormone secretion

Taking iodine is the main function of the thyroid gland. This iodine is found in many foods and using this iodine the thyroid gland converts it to thyroid hormones. The hormones are thyroxine and triiodothyronine. The only cells in the body that can absorb iodine are thyroid cells. To make T3 and T4 iodine is combined with amino acid tyrosine. Then these hormones are released into the blood stream. From the blood they are transported throughout the body. Controlling the metabolism is one of the functions they perform.


Boosting the basal metabolic rate including fats, carbohydrates, proteins and vitamins is the main activity of the thyroid hormones T3 and T4.

Cardiovascular functions

For cardiac function and cardiovascular hemodynamics, thyroid hormone is an important regulator. Triiodothyronine mediates the expression of several important cardiac genes by binding to nuclear receptors. It induces transcription of alpha-myosin heavy chain that is a positively regulated genes. In the presence of normal serum level of thyroid hormones the negatively regulated genes such as beta MHC are down regulated. Relaxation of vascular smooth muscles causes decreased diastolic blood pressure and atrial resistance which are the T3 mediated effects on the systemic vasculature.

Developmental functions

In brain development and function, thyroid hormone plays a very important role. The active form of thyroid hormone is triiodothyronine that controls the gene expression.  They are involves in cell differentiation, migration, signalling and myelination. Cognitive problems can occur If there is deficiency of thyroid hormones. Even for the fetal and neonatal brain development thyroid hormones are very important. In both animals and humans the importance of thyroid hormones in neurological development has been observed. On the individuals neurological function there can be irreversible adverse effects if there is a deficit in thyroid hormones during the fetal development.  By binding to T3 nuclear receptors, thyroxin and triiodothyronine act on the brain development and maturation.

Sexual function

For sexual development during puberty, T3 and T4 are needed.  Thyroid hormone plays a role is development of pubic and axillary hair, breast in girls, beard and moustache in boys, in both sexes development of genital organs and in girls menstrual functions. Also performance of sex and libido is related to thyroid function.  Also related to it is production of eggs and sperms.


For regulation of their metabolism every cell in the body depends on the thyroid hormones.  80 percent of T4 and 20 percent of T3 is produced by normal thyroid gland but the strength possessed by T3 is four times than that of T4.  The pituitary responds by decreasing the production of TSH. Hence the hormones are regulated. Both the glands pituitary and thyroid gland function like a thermostat. Hypothalamus regulates the pituitary gland. It produces TRH that stimulates the thyroid gland to release TSH.

Calcitonin production

The thyroid gland also releases calcitonin if the amount of calcium in the blood is high then this hormone is released. In the blood it decreases the amount of phosphorus and calcium by slowing the activity of osteoclasts.  Also the rate at which calcium and phosphorus is taken up by bone is accelerated by calcitonin. To regulate calcium levels, calcitonin works with parathyroid hormone.

Proteins breakdown

In the metabolism of protein, thyroid hormone plays an important role. The thyroid hormone can stimulate the synthesis of proteins and well as its degradation. Protein synthesis can be affected by deficiency of thyroid hormone. Protein synthesis is a very important process.

Voice quality

Closely located near our vocal cord is the thyroid gland and on the sound of our voice it has profound effect. If the thyroid gland is overactive then it may cause the sound to produce a rough hoarse voice. Particularly when females are affected during menopause this sound is prominent. Thyroid hormone can have a tremendous impact in the function and structure of the vocal apparatus.