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Unformatted text preview: Lecture 39: Peripheral Endocrine Glands - Thyroid and Adrenal Reading: chapter 19, pgs 683-701 (5 th edition 701-719) Thyroid Gland Anatomy (Figure 19-1) Follicular cells - secrete tetraiodothyronine (T4, or thyroxin) and triiodothyronine (T3). Colloid ( A CAVITY ) thyroglobulin ( SITE OF SYNTHESIS ) (produced by follicular cells). Thyroid hormone - synthesis, storage, secretion and transport (Figure 19-2)- Tyrosine and iodine are required for thyroid hormone synthesis.- All steps from synthesis to secretion take place on thyroglobulin: 1) Thyroglobulin is produced in the ER/Golgi of follicular cells and is then secreted into the colloid. Thyroglobulin contains many tyrosines. 2) Iodine is actively transported from the blood into the colloid. Almost all iodine in the body is collected by the thyroid. ( THE PUMP HYDROLYZES ( USES ) ATP ) 3) In colloid, individual tyrosines become either mono- or di-iodinated (MIT or DIT). ( LIPOPHILIC ) 4) While still on the thyroglobulin, tyrosines couple together. Coupling of two DITs produces T4. Coupling of one DIT and one MIT produces T3. MITs do not couple together. Thyroglobulin-hormone complex within colloid represents the storage condition. 5) Upon stimulation, follicular cells phagocytize a piece of the colloid. 6) Endocytotic vesicle fuses with lysosome. Lysosomal enzymes cleave the colloid, releasing T4, T3, DIT and MIT. T4 and T3 are highly lipophilic and diffuse through the outer membrane into the blood....
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- Winter '08