Question

In the thyroid hormones, T3 and T4, the 3 and 4 refer to the?

1) relative half-life (3 or 4 hours)
2) number of tyrosine molecules linked together
3) number of iodines which are found on the hormone
4) number of enzymes required to synthesize the hormone

Answer 1

In the thyroid hormones T3 and T4, the numbers represent the number of iodine atoms each contains, with T3 having three and T4 having four. These hormones play a crucial role in regulating the body's metabolic rate.Hence, the correct answer is option 3.

Step-by-step explanation:

In the thyroid hormones, T3 (triiodothyronine) and T4 (thyroxine or tetraiodothyronine), the numbers 3 and 4 refer to the number of iodine atoms attached to the hormone structure. T3 contains three iodine atoms, whereas T4 contains four iodine atoms. These hormones are essential for controlling the body's basal metabolic rate.

Thyroid hormone production is stimulated by the thyroid-stimulating hormone (TSH), which is released from the anterior pituitary gland. The precursor to these hormones is a glycoprotein called thyroglobulin that is present in the follicles of the thyroid gland. Iodide ions are actively transported into the thyroid follicle, converted to iodine, and then attached to tyrosine amino acids within thyroglobulin to form T3 and T4. After synthesis, T3 and T4 are released into the bloodstream where T4 can be converted to T3 in target tissues, given that T3 is the more active form.

It is also important to note that the majority of T3 and T4 in the bloodstream is bound to transport proteins, maintaining a reserve and regulating hormone activity. The process of up-regulation refers to the increase in the number of hormone receptors in response to increased levels of a hormone.