Tiroxín

Tiroxín, also known as thyroxine or T4, is a thyroid hormone produced by the thyroid gland. It plays a crucial role in regulating metabolism, growth, and development in the body. T4 is a prohormone, meaning it is converted into the more active form, triiodothyronine (T3), in various tissues.

The synthesis of tiroxín involves the uptake of iodine by the thyroid gland, which is then incorporated into tyrosine residues of the protein thyroglobulin. This process, called iodination, is followed by the coupling of iodinated tyrosine residues to form T4. The release of T4 from thyroglobulin into the bloodstream is stimulated by thyroid-stimulating hormone (TSH), which is produced by the pituitary gland.

Once in circulation, tiroxín binds to transport proteins, primarily thyroxine-binding globulin (TBG), albumin, and transthyretin. This binding helps maintain a stable level of free T4 in the blood, which is the biologically active form. Tissues can then convert T4 into T3, the more potent hormone, through deiodination.

Tiroxín affects virtually every cell in the body. It influences basal metabolic rate, increasing oxygen consumption and heat production. It is essential for normal growth and development, particularly in children, impacting bone maturation and brain development. Hormonal imbalances related to tiroxín can lead to various conditions, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid), with symptoms affecting energy levels, weight, heart rate, and cognitive function.