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Endocrine Physiology.docx

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Physiology 3120
Tom Stavraky

Endocrine Physiology Introduction Endocrine System tissuescells capable of secreting and responding to hormones Communication system Two components communicate via chemical messengers called hormones Neural functions mediated by electrochemical conduction along nerves Endocrine functions are mediated by chemical messengers called hormones Hormone oChemical substance formed in one organ or part of the body and carried in the blood to another organ or part oDepending on specificity of their effects hormones can later the functional activity of just one organ or various organs oRegulators of physiologic events oEffective in minute quantities oSynthesized by cellsendocrine glands oGreek hormon to rouse or set in motion Endocrine chemical mediators produced in one organ which acts on a distant part remote controlParacrine chemical mediators produced in one cell that acts on neighboring cell neighborhood watch Autocrine chemical mediators produced in one cell and acts on that same cell self control Nervous System vs Endocrine System oPhysical form of information transfer action potentials vs chemicalsoSpeed of information transfer fractions of seconds vs minutes hours daysoMechanism of gradation frequency vs amplitude modulationoMechanism to achieve specificity wiring vs receptorsHormone Types oPeptidePolypeptide Small monomersEx TRH 3 AA Large multimeric proteinsEx TSH FSH LH 200 AA Water soluble Ex TRHoSteroid Derived from cholesterol metabolism 4 hydrocarbon rings with various side chains Lipid soluble require binding proteins in serum Ex testosterone estrogen vitamin D oAmino Acid Derivatives Ex epinephrine thyroxine T 4Human Endocrine System Gut secretes its own series of hormones to regulate food intakedigestion CCK ghrelin gastrin secretin NPYHeart secretes ANP important factor in regulating vascular tonevolumeKidneys secrete EPO which increases erythrocyte formationLiver secretes angiotensinogen angiotensin precursor IGFIthrombopoietinplateletsFat produces many adipokines ex leptinCells produce locallyacting growth factors and cytokinesRegulation of Endocrine Secretion I Negative Feedback Between 2 Hormones Between HormoneMetaboliteBetween 2 Antagonist Hormones Regulation of Endocrine Secretion II Positive Feed Forward Characteristics of All HormonesReceptor SpecificityOnly certain cells respond to a given hormoneSome cells are targets for more than one hormone Cell must have the appropriate receptor to respond to a hormone Some receptors can be promiscuous and bind to more than one hormone Multiple Effects of a Single HormoneA single hormone may elicit different responses in each target tissueTestosteronepasses into cell membrane
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