Answer:
The steps in the production of thyroid hormone in the order in which they occur is: 1, 2, 4, 5, 3.
Explanation:
The thyroid gland is an organ located anterior to the trachea and inferior to the larynx. The tissue of the thyroid gland is composed of thyroid follicles, which are made up of a central cavity filled with a sticky fluid called colloid. The colloid is surrounded by a wall of epithelial follicle cells and it is the center of thyroid hormone production. The process of thyroid hormone production is dependent on iodine.
The following steps outline the processes involved in thyroid hormone production:
- The thyroid-stimulating hormone (TSH) binds to its receptor in the follicle cells of the thyroid gland, which causes the cells to actively transport iodide ions across their cell membrane, from the bloodstream into the cytosol. making the concentration of iodide ions in the follicular cells higher than that in the bloodstream.
- Iodide ions move to the lumen of the follicular cells that border the colloid. Thereafter, the ions undergo oxidation, which means that their negative charge is removed. The oxidation of two iodide ions results in iodine, which passes through the follicle cell membrane into the colloid.
- In the colloid, peroxidase enzymes link the iodine to tyrosine in thyroglobulin to produce two intermediates: a tyrosine attached to one iodine and a tyrosine attached to two iodines.
- When a tyrosine attached to one iodine is linked by covalent bonds to a tyrosine attached to two iodines, the resulting compound is a triiodothyronine (T3) which is a thyroid hormone with three iodines. When two tyrosines attached to two iodines are covalently bonded, they form a tetraiodothyronine, also known as thyroxine (T4) a thyrroid hormone with four iodines
- These hormones remain in the colloid center of the thyroid follicles until TSH stimulates endocytosis of colloid back into the follicular cells, where the hormones are then stored.
