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Endocrine Physiology

Endocrine Physiology. Bob Bing-You, MD, MEd, MBA Medical Director Maine Center for Endocrinology. What is physiology?. A. Study of function in living matter B. Specific characteristics and mechanisms of the human body that make it a living being

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Endocrine Physiology

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  1. Endocrine Physiology Bob Bing-You, MD, MEd, MBA Medical Director Maine Center for Endocrinology

  2. What is physiology? • A. Study of function in living matter • B. Specific characteristics and mechanisms of the human body that make it a living being • C. “The human being is actually an automaton.” • D. All of the above.

  3. Learning Objectives • Explain normal feedback mechanisms for normal endocrine function • Describe abnormal pathophysiologic states • Define treatment approaches for such states

  4. Ground Rules • Case-based, common examples • Feel to ask questions anytime • Take a few breaks for Q and A • Call or e-mail [bingyb@mmc.org] with confused thoughts, concepts, etc.

  5. Major Areas • Thyroid gland • Adrenal gland function, steroid Rx • Diabetes: glucose monitoring, insulin Rx • Calcium homeostasis, vitamin D • Pheochromocytoma • Diabetes insipidus

  6. Design Exercise • New heat source for your house in the basement • Need monitor system 3 floors above • Thermostats not invented yet! • Task= design system to regulate temperature in your house

  7. Purpose of Endocrine System • Principally concerned with control of different metabolic functions of the body [e.g., transport of substances through cell membranes] • Hormonal effects can occur in seconds while others require days or weeks

  8. What is a hormone? • A chemical substance secreted into body fluids by one cell or group of cells • Exerts a physiological control effect on other cells in the body • General vs. local hormones • General hormones may effect all cells [e.g. GH] or some effect specific tissues

  9. Major Hormones • Anterior pituitary • Growth hormone • Adrenocorticotropin [ACTH] • Thyroid-stimulating hormone [TSH] • Follicle-stimulating hormone [FSH] • Luteinizing hormone [LH] • Prolactin [PRL]

  10. More Hormones • Posterior pituitary: antidiuretic hormone [ADH] • Adrenal • Aldosterone • Glucocorticoids [cortisol] • Testosterone, estrogen • catecholamines

  11. Even More Hormones! • Thyroid hormones: thyroxine [T4], triiodothyronine [T3] • Pancreatic: insulin, glucagon • Parathyroid: parathyroid hormone [PTH]

  12. Chemistry of Hormones • Two types • Proteins or derivatives of proteins or amino acids [e.g., anterior pituitary, thyroid] • Steroid hormones [e.g., adrenal cortex, gonads] • Circulate in minute quantities [e.g., one-millionth of a milligram] • Bioassay vs. radioimmunoassay

  13. What describes hormones effecting other local cells? • A. Paracrine • B. Endocrine • C. Autocrine • D. None of the above.

  14. Bioassay • Animal cell tissue system • Plasma or some extract added to see effect • E.g., testosterone

  15. Immunoassay • Sandwich-type • Very quick [e.g., intra-op PTH] • Minimal blood or serum required

  16. Mechanisms of Action • Activation of cyclic AMP system of cells • Need hormone receptor [key and lock] • Cyclic AMP forms as an intracellular hormonal mediator [aka as “second messenger”] • ACTH, TSH, FSH, LH, ADH, PTH, glucagon • Effects can be instantaneous

  17. 2nd mechanism of action • Activation of genes in target cells, causing formation of intracellular proteins • Steroid hormone enters cytoplasm and binds to receptor proteins • Enters nucleus to activate genes to form messenger RNA • m-RNA promotes new proteins to be made • Delayed effect of mins [aldosterone] to days

  18. Transport of Hormones • Biologic effect due to free hormones • Binding globulins – “the buses” • Thyroid Binding Globulin [TBG] • Sex-hormone Binding Globulin [SHBG] • Cortisol Binding Globulin [CBG] • Produced in liver • What is assay measuring? “Total” [I.e., bound] vs. “Free”

  19. Sandwich-type assays refer to: • A. Dialysis method • B. Ham and cheese • C. Two antibodies • D. Live cellular responses

  20. Control of Hormonal System • Tendency of each gland is to oversecrete • Need method to prevent oversecretion • Need method to stimulate production if undersecreting • KEY is Negative Feedback • Some exceptions [e.g., prolactotrophs and dopaminergic inhibitory fibers]

  21. Key Points • Hormones effect metabolism all tissues • Instantaneous vs. prolonged effects • Free hormones biologically active • Negative feedback is KEY to normal homeostasis

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