Скачать или смотреть Thyroid hormone Functions | Lecture 2 | Pharmacology | Lipincott

Thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), are crucial regulators of metabolism and play vital roles in the development and function of nearly every cell and organ system in the body. While T4 is produced in larger quantities, it's largely considered a prohormone, as T3 is the more active form, often converted from T4 in target tissues.


Key Functions of Thyroid Hormones:

Metabolic Rate Regulation: Thyroid hormones significantly increase the basal metabolic rate (BMR), influencing how quickly the body converts food into energy. This affects weight management, energy levels, and body temperature.

Growth and Development: They are essential for proper growth and development, particularly of the brain and nervous system in infants and children. They also play a role in bone growth and maturation.

Cardiovascular System: Thyroid hormones impact heart rate, the strength of heart contractions, and overall cardiac output.
Nervous System: They influence brain function, mood, memory, and cognitive processes. Imbalances can lead to symptoms like anxiety, irritability, depression, or impaired memory.
Digestive System: Thyroid hormones affect the speed at which food moves through the digestive tract.
Skin, Hair, and Nails: They contribute to the maintenance and health of skin, hair, and nails by regulating cell turnover.
Reproductive System: Proper thyroid hormone levels are important for fertility and regular menstrual cycles.
Other Functions: They also influence protein synthesis, fat and carbohydrate metabolism, and oxygen consumption.
Regulation of Thyroid Hormones:

The production and release of thyroid hormones are tightly controlled by a sophisticated feedback loop involving the hypothalamus, pituitary gland, and thyroid gland, collectively known as the Hypothalamic-Pituitary-Thyroid (HPT) axis.

Hypothalamus: When thyroid hormone levels are low, the hypothalamus (a part of the brain) releases Thyrotropin-Releasing Hormone (TRH).
Pituitary Gland: TRH travels to the anterior pituitary gland, stimulating it to release Thyroid-Stimulating Hormone (TSH).
Thyroid Gland: TSH then signals the thyroid gland to:
Uptake iodide from the bloodstream (iodide is an essential component of thyroid hormones).
Synthesize thyroid hormones (T3 and T4) using iodine and the protein thyroglobulin.
Release T3 and T4 into the bloodstream.
Negative Feedback Loop:

Once T3 and T4 levels in the blood rise, they exert a negative feedback on the hypothalamus and pituitary gland. This means that high levels of thyroid hormones inhibit the release of TRH from the hypothalamus and TSH from the pituitary. This inhibition reduces the stimulation of the thyroid gland, thus preventing excessive hormone production and maintaining a stable balance of thyroid hormones in the body.



This intricate regulatory system ensures that the body has the appropriate amount of thyroid hormones to maintain its metabolic functions and overall health. Disruptions in this delicate balance can lead to conditions like hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid), both of which can have significant impacts on health.