Final answer:
c) Enhances thyroid hormone synthesis.
Levothyroxine (Synthroid) primarily enhances thyroid hormone synthesis and stimulates the basal metabolic rate in the body, treating hypothyroidism.
Step-by-step explanation:
The primary action of levothyroxine (Synthroid) is to enhance thyroid hormone synthesis. Levothyroxine is a synthetic form of thyroxine (T4), one of the hormones produced by the thyroid gland. Its main function is to stimulate the metabolism throughout the body. Levothyroxine is used to treat hypothyroidism, a condition in which the thyroid gland does not produce enough thyroid hormones. When taken, levothyroxine is converted to triiodothyronine (T3), which enters the cells and stimulates the basal metabolic rate.
Thyroid-Stimulating Hormone (TSH) released from the anterior pituitary gland regulates the activity of the thyroid by promoting the release of T3 and T4. TSH is stimulated by thyrotropin-releasing hormone (TRH) from the hypothalamus and works on a classic negative feedback loop. High levels of T3 and T4 in the blood decrease the production and secretion of TSH.