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Endocrine overview

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Western University
Physiology 3120
Tom Stavraky

Human Physiology Friday, February 12, 2010 “Endo I” Overview • Endocrine system  Tissues and cells capable of secreting/responding to hormones  Hormone  A chemical substance produced in one part of the body that is secreted into the bloodstream and then circulates throughout the body; but a lot of variability  Can affect one or a number of organs (i.e. GnRH vs. T3)  Regulators of physiological events  Effective in small quantities (i.e. high affinity)  Synthesized by cells or glands  Some hormones can act in different ways (i.e. paracrine signalling; autocrine signalling) • Nervous vs. endocrine system  Two ways that our body exerts control; work together  Physical form of info transfer  Endocrine  chemical messenger; nervous  AP  Speed  Endocrine  minutes/hours/days; nervous  seconds  Mechanism of gradation (strength)  Endocrine  amplitude (concentration) of hormone; nervous  frequency of AP  Mechanism for specificity  Endocrine  receptors; nervous  “wiring” • Endocrine system  Many major glands (i.e. hypothalamus, pituitary [master control system], adrenals, thyroids, gonads, pancreas, etc.)  Many other cells that aren’t in discrete glands that also produce hormones  Gut cells secrete many hormones (i.e. gastrin, secretin, CCK)  Heart cells secrete ANP  Kidneys secrete EPO  Liver secretes IGF-1 and angiotensinogen  Fat cells produce leptin • Regulation of hormones  Negative feedback  Between 2 hormones (i.e. TSH and T 3 T 3nhibits TSH release from pituitary)  Between a hormone and a metabolite (i.e. parathyroid hormone & Ca)  Between antagonistic pairs of hormones (i.e. insulin & glucagon on glucose metabolism)  Positive feed forward  Reproductive cycle; rising level of estrogen stimulates release of LH • Classes of hormones  Peptide hormones  Small monomers, or they can be large multimeric proteins  Water soluble; freely dissolve in blood plasma; can’t cross cell membrane  Cell-surface receptors (i.e. GPCRs, Tyr-kinase receptors, receptor-mediated ion channels) • Largest class of cell-surface receptors (over 800 with known function) • Beta-gamma subunits have physiological function as well as the alpha; many different G-alphas (see Phys 3140a notes)  Translation usually produces a “prohormone” (still has signal sequence in it); often modified post-translationally in Golgi; secreted in vesicles in response to some signal (usually an increase in intracellular Ca)  Ster
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