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BIOS 472, Spring 2001 Introduction to Endocrinology Hormone: specialized, specific chemical substances synthesized by specialized tissues that are secreted into and carried by the blood stream to target organs and cells where they produce specific biological effects. How to study the endocrine system: Where appropriate, understand the following points with respect to each of the major hormones: 1. The origin within a gland 2. The synthesis and structure of the hormone 3. Storage 4. Secretion and its control (i.e., feedback loops) 5. Transport 6. Primary sites of action 7. Metabolism and secretion 8. Pathophysiology – hyposecretion, hypersecretion, dysfunction Hormone categories 1. Amino acid derivatives 2. Peptide/protein hormones 3. Steroid hormones Glucocorticoids Mineralcorticoids Androgens Estrogens Progestins Calciferols The thyroid gland -- Maintains the optimal level of metabolism for tissues Stimulate the O2 consumption for most of the cells of the body Helps regulate lipid and carbohydrate metabolism Necessary for growth and maturation The thyroid is regulated by thyroid stimulating hormone (TSH) from the anterior pituitary. TSH is, in turn, regulated by thyrotropin releasing hormone from the hypothalamus The principle hormones secreted by the thyroid are thyroxin (T4) and triiodothyronine (T3). The thyroid hormones enter cells and bind to thyroid receptors in the nuclei (T 3 binds much more avidly than T4) Specific effects Calorigenic Nervous system Cardiac tissue Skeletal muscle Carbohydrate metabolism The pituitary and growth The posterior pituitary is made up lagely of the endings on blood vessels of axons from the supraoptic and paraventricular nuclei of the hypothalamus. ADH (anti-diuretic hormone) Oxytocin The anterior pituitary has a special vascular connection with the hypothalamus Thyroid stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) Prolactin Growth hormone (GH, somatotropin) Growth hormone Chondrogenesis is accelerated Viscera growth Increase protein mass/decrease fat mass Somatomedins – polypeptide growth factors secreted by the liver and other tissues in response to stimulation by GH Insulin-like growth factor I (IGF- I) Insulin-like growth factor II (IGF-II) In general, GH doesn’t directly affect growth, but rather sets cells up to respond to IGF. For example, GH acts on cartilage to convert stem cells into cells that respond to IFG-I, that promotes chondrogenesis GH is regulated through the hypothalamus. GHRH from hypothalamus triggers GH release. GHRH = GH = IGF-I = GH release Of course, growth is a complex phenomena that is affected by not only GH and Somatomedins, but thryoid hormones, androgens and estrogens, glucocorticoids, insulin, and proper nutrition.