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lecturenotes36-41

lecturenotes36-41 - Lecture 36 Principles of Endocrinology...

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Lecture 36: Principles of Endocrinology Reading: review chap 4 pgs 113-125; read chap 18, pgs 653-662 (5 th edition 667-681) Endocrinology Study of the control of physiological processes by the system of cells, tissues, organs and glands that secrete hormones. Hormone Chemical produced by one cell which enters the bloodstream, is transported to a different body location, and then binds to a specific receptor on a target cell(s), altering function of the target. Human body has two major control systems: Nervous system Endocrine system - rapid, short-acting signals - slower acting, longer lasting signal - precise, direct interconnections - diffuse, indirect connections (via blood) Endocrine signaling ( Figure 18-4, 5 th edition only ): endocrine gland -> hormone -> receptor binding -> postreceptor events -> response General functions of endocrine system (1) Homesostasis - regulates composition and volume of ECF - controls energy production - controls digestive tract and organ function - induces adaptation to hostile environment (2) Reproduction (3) Growth and development (4) Behavior Hormones Tropic hormones stimulate and maintain their endocrine target tissues e.g. thyroid stimulating hormone (TSH). TSH is derived from the anterior pituitary and acts on the thyroid gland to stimulate secretion of thyroid hormone. It is also responsible for maintaining the thyroid gland. Therefore a decrease in TSH will lead both to decreased production of thyroid hormone and to atrophy of the thyroid gland (it shrinks). Non-tropic hormones exert effects on non-endocrine target tissue e.g. thyroid hormone acts on almost every cell in the body to regulate metabolic activity. Criteria for determining if a substance is a hormone - gland removal leads to a specific homeostatic problem (i.e. remove adrenal cortex, excessive Na loss, death) - extracts from gland correct problem - purified synthetic hormones correct problem - time-course of hormone release is physiologically relevant
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3 Classes of Hormones Peptides and proteins - small chains of amino acids (3-200 aa long) - synthesis: transcription and translation - processed in Golgi complex - Cleave pre and pro portions - mature hormones stored in secretory granules until released by exocytosis - are hydrophilic (water soluble) Amines Are derived from naturally occurring amino acids Examples: tyrosine -> thyroid hormones (in thyroid gland) tyrosine -> epinephrine (in adrenal medulla) tryptophan -> melatonin (in pineal gland) Steroids - derived from cholesterol (Figure 4-23; 18-3 ) - lipophilic (fat soluble) - once synthesized, steroid immediately diffuse through the plasma membrane into blood - in blood, reversibly bound to plasma proteins - because the body does not produce degradation enzymes for steroids or thyroid hormones, such lipophilic hormones can be introduced orally. Postreceptor events Hydrophilic hormones generally act through G proteins coupled to cAMP intracellular signaling pathways (Figure 4-24; 3-23 ).
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