![]() ![]() rT3 is inactive and forms by type 3 deiodinase activity on T4. The third iodothyronine is called reverse T3, or rT3. In the brain, T4 is converted to active T3 by type 2 deiodinase produced by glial cells. ![]() T4 is converted to T3 peripherally by type 1 deiodinase in tissues with high blood flow, such as the liver and kidneys. The primary secretory product is inactive thyroxine, or T4, a prohormone of triiodothyronine, or T3. ![]() The thyroid gland is responsible for the production of iodothyronines, of which there are three. The connective tissue of the thyroid gland forms from invading neural crest cells. Cells from the ultimobranchial bodies invade the developing thyroid and form the parafollicular cells, or C cells, which will produce calcitonin. The isolated thyroid gland develops two distinct lobes connected by an isthmus of tissue by this time and continues to descend and reaches its final destination by the end of the seventh week of development. The only remaining aspect of the thyroid’s embryonal development will be the foramen cecum at the base of the developed tongue. In normal development, the thyroglossal duct deteriorates by the end of the fifth week. ![]() This mass of endoderm migrates down through the developing neck via the thyroglossal duct toward its eventual home, just inferior to the cricoid cartilage. The thyroid diverticulum first forms at the end of the fourth week of development as a solid, proliferating mass of endoderm at the foramen cecum on what will become the tongue. ![]()
0 Comments
Leave a Reply. |