Disorders of Thyroid Function Endocrinology 甲状腺功能紊乱的内分泌.ppt

Anatomy of the Thyroid Gland Follicles: the Functional Units of the Thyroid Gland The Thyroid Produces and Secretes 2 Metabolic Hormones Two principal hormones Thyroxine (T4 ) and triiodothyronine (T3) Required for homeostasis of all cells Influence cell differentiation, growth, and metabolism Considered the major metabolic hormones because they target virtually every tissue Thyroid-Stimulating Hormone (TSH) Regulates thyroid hormone production, secretion, and growth Is regulated by the negative feedback action of T4 and T3 Hypothalamic-Pituitary-Thyroid AxisNegative Feedback Mechanism Production of T4 and T3 T4 is the primary secretory product of the thyroid gland, which is the only source of T4 The thyroid secretes approximately 70-90 ?g of T4 per day T3 is derived from 2 processes The total daily production rate of T3 is about 15-30 ?g About 80% of circulating T3 comes from deiodination of T4 in peripheral tissues About 20% comes from direct thyroid secretion T4: A Prohormone for T3 T4 is biologically inactive in target tissues until converted to T3 Activation occurs with 5 iodination of the outer ring of T4 T3 then becomes the biologically active hormone responsible for the majority of thyroid hormone effects Thyroid Hormones Stimulate Metabolic Activities in Most Tissues Thyroid hormones (specifically T3) regulate rate of overall body metabolism T3 increases basal metabolic rate Calorigenic effects T3 increases oxygen consumption by most peripheral tissues Increases body heat production Metabolic Effects of T3 Stimulates lipolysis and release of free fatty acids and glycerol Induces expression of lipogenic enzymes Effects cholesterol metabolism Stimulates metabolism of cholesterol to bile acids Facilitates rapid removal of LDL from plasma Generally stimulates all aspects of carbohydrate metabolism and the pathway for protein degradation Additional Effects of T3 Initiates or sustains differentiation and growth Stimulates formation of proteins, wh