Thyroid hormone synthesis

Definition

Thyroid hormone synthesis is the biochemical process through which the thyroid gland produces hormones, primarily thyroxine (T4) and triiodothyronine (T3), from iodide and the amino acid tyrosine. This process involves a series of steps including the uptake of iodide, its oxidation and incorporation into thyroglobulin, and the enzymatic conversion to the active hormones. The production of these hormones plays a critical role in regulating metabolism, growth, and development in the body.

5 Must Know Facts For Your Next Test

1. Thyroid hormone synthesis begins with the active transport of iodide into thyroid follicular cells, where it is oxidized to iodine.
2. Once iodide is oxidized, it is incorporated into thyroglobulin to form iodinated tyrosine residues, which are crucial for the formation of T3 and T4.
3. The process is regulated by TSH, which increases the activity of enzymes responsible for hormone synthesis and release.
4. T3 is biologically more active than T4, but T4 is produced in greater quantities; about 80% of circulating thyroid hormones are in the form of T4.
5. After synthesis, T3 and T4 are released into the bloodstream bound to transport proteins, allowing them to circulate and exert their metabolic effects.

Review Questions

• What are the main steps involved in thyroid hormone synthesis, and how do they relate to each other?
  • Thyroid hormone synthesis involves several key steps: first, iodide is actively transported into thyroid follicular cells. Next, iodide is oxidized to iodine and incorporated into thyroglobulin, creating iodinated tyrosine residues. Finally, enzymatic reactions convert these residues into T3 and T4. Each step is essential for proper hormone production, highlighting how closely linked they are in maintaining hormonal balance.
• Discuss the role of TSH in regulating thyroid hormone synthesis and how it impacts metabolic processes in the body.
  • TSH plays a crucial role in regulating thyroid hormone synthesis by stimulating the thyroid gland to produce T3 and T4. When levels of these hormones are low, TSH secretion increases from the pituitary gland, promoting iodide uptake and enhancing enzymatic activity in hormone production. This regulation is vital because thyroid hormones influence metabolic processes such as energy expenditure, growth, and overall metabolic rate.
• Evaluate how deficiencies in iodine affect thyroid hormone synthesis and what physiological consequences arise from this condition.
  • Iodine deficiency significantly disrupts thyroid hormone synthesis because iodine is an essential component required for producing T3 and T4. Without adequate iodine levels, the thyroid cannot synthesize sufficient amounts of these hormones, leading to conditions like hypothyroidism or goiter. Physiologically, this can result in symptoms such as fatigue, weight gain, and developmental issues in children due to impaired metabolism and growth regulation.

Related terms

Thyroglobulin: A large glycoprotein produced by the thyroid gland that serves as a precursor for thyroid hormones, providing a scaffold for iodine incorporation.

Iodine: An essential element required for the synthesis of thyroid hormones, as it is incorporated into T3 and T4 molecules during their formation.

TSH (Thyroid-Stimulating Hormone): A hormone produced by the pituitary gland that stimulates the thyroid gland to produce T3 and T4, regulating overall thyroid function.