What are the Normal Values and Functions of Thyroid Hormone?
The normal values of thyroid hormones cannot be generalized as thyroid hormones include five types: serum thyroxine, serum free thyroxine, serum triiodothyronine, free triiodothyronine, and serum thyrotropin. They play crucial roles in promoting growth and development, regulating metabolism, and maintaining neural excitability.
I. Normal Values of Thyroid Hormones
The normal range of serum thyroxine is 65-155nmol/L, serum free thyroxine is 10.3-31.0pmol/L, serum triiodothyronine is 1.8-2.9nmol/L, free triiodothyronine is 2.0-6.6pmol/L, and serum thyrotropin is 0.3-5.0mU/L.
II. Functions of Thyroid Hormones
1. Promoting Growth and Development
Thyroid hormones play a significant role in promoting growth and development, especially during infancy. Their effect is most profound within the first four months after birth, primarily promoting the growth and development of bones, brain, and reproductive organs. Without thyroid hormones, the GH produced by the pituitary gland cannot function effectively. Moreover, a lack of thyroid hormones can lead to a decrease in the production and secretion of GH by the pituitary gland, resulting in conditions such as cretinism in congenital or childhood hypothyroidism.
2. Affecting Metabolism and Heat Production
Thyroid hormones increase the oxygen consumption rate of most tissues, enhancing heat production. This effect may be due to their ability to increase the synthesis and activity of the Na+-K+ pump on cell membranes, which is an energy-consuming process. Thyroid hormones increase the basal metabolic rate, with 1mg of thyroxine increasing heat production by 4000KJ. In patients with hyperthyroidism, the basal metabolic rate may increase by approximately 35%, while in patients with hypothyroidism, it may decrease by approximately 15%.
3. Maintaining Neural Excitability
Thyroid hormones also play a crucial role in maintaining neural excitability. They can directly act on the myocardium, promoting the release of Ca2+ from the sarcoplasmic reticulum, enhancing myocardial contractility and increasing heart rate.
