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Endocrine System

Endocrine System. Dr Khamis Al Hashmi Department of physiology Room # 006 Ext. 3435 Email: kh@squ.edu.om. Nervous Vs Endocrine system. Nervous and endocrine systems acts together to coordinate functions of body system. Nervous system releases; Neurotransmitors

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Endocrine System

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  1. Endocrine System Dr Khamis Al Hashmi Department of physiology Room # 006 Ext. 3435 Email: kh@squ.edu.om

  2. Nervous Vs Endocrine system • Nervous and endocrine systems acts together to coordinate functions of body system. • Nervous system releases; Neurotransmitors • Endocrine system releases; Hormones

  3. Nervous Vs Endocrine system (cont.)

  4. Endocrine Vs Exocrine glands • Exocrine gland: secrete their products into ducts that carry the secretion into body cavities, into lumen of organs, or to the outer surface of the body. • E.g. Sweat, sebaceous, mucus, digestive glands. • Endocrine glands: secrete their products into the interstitial fluid surrounding the secretory cells diffused into blood capillaries carried to target cells.

  5. Definitions Hormone: is a mediator molecule that is released in one part of the body but regulates activity of cells in other parts of the body. Target cell: A cells whose activity is affected by a particular hormone. Receptor:A specific molecule or cluster of molecules that recognizes and binds a particular ligand (hormone)

  6. Circulating hormones Vs Local hormones A) Circulating hormones

  7. B) Local hormones: 1) Paracrines E.g. Nitric oxide. IL2

  8. 2) Autocrines E.g. IL2 Local hormones usually are inactivated quickly

  9. Chemical classes of hormones • Water-soluble hormones: • Amine hormones (Retain an amino group (NH3+) • Peptide and protein hormones • Eicosanoid hormones (derived from arachidonic acid. Eg. Prostaglandins, leukotrienes) • Lipid-soluble hormones: • Steroid hormones • Thyroid hormones • Nitric oxide

  10. a) Water soluble hormone

  11. b) Lipid soluble hormone

  12. Hormone transport in the blood • Water soluble hormones circulate in a free form (Unbound). • Lipid soluble hormones bound to transport proteins. (>90%). Importance: • Increase the solubility in blood. • Slow the rate of excretion by kidney or degradation by liver. • Provide a ready reserve of hormone.

  13. Responsiveness of a target cell to a hormonedepend on: • Concentration of the hormone • Number of receptors • Influence by other hormone (hormones interaction) • Concentration of the hormone • The hormone’s rate of secretion (all hormones) • Rate of metabolic inactivation and excretion (all hormones) • Rate of metabolic activation (few hormones) • Extent of binding to plasma protein (lipophilic hormones)

  14. Control of hormone secretion • Important to prevent overproduction or underproduction Three types of signals: • Signals from the nervous system Eg. Nerve impulse to adrenal medulla Epinephrine • Chemical changes in the blood. Eg. Blood Ca2+ level parathyroid hormone • Other hormone Eg. Ant. Pituitary hormones hormones of other glands

  15. Negative-feedback control Short loop feedback long loop feedback

  16. Positive-feedback control

  17. Diurnal (circadian) rhythm • The secretion rate of many hormones rhythmically fluctuate up and down as function of time. • Diurnal (or circadian),i.e. “day-night”. characterised by repetitive oscillations in hormone levels that are very regular and have a frequency of one cycle every 24 hours. Eg. Cortisol secretion. • Other. Monthly menstrual period. • Negative feedback control mechanisms operate to maintain whatever set point is established for that time.

  18. Clearance of hormones from the blood • Metabolic destruction by the tissues • Binding with the tissues. • Excretion by the liver into the bile. • Excretion by the kidneys into urine.

  19. 2) Number of receptors Down regulation: A hormone present in excess Receptors • Destruction of the receptor by lysosomes • Decrease production of receptors • Inactivation of some of the receptor molecules • Inactivation of some of the intracellular signaling molecules • Temporary sequestration of the receptor to the inside of the cell. Up regulation: A hormone is deficient Receptors

  20. 3) Hormones interaction: Permissiveness (permissive effect): powerful action of a hormone on target cells require a simultaneous or recent exposure to a second hormone. Eg. Epinephrine and thyroid hormones in lipolysis. Synergism (synergistic effect): the effect of two hormones acting together is greater or more extensive than the effect of each hormone acting alone. Eg. FSH and estrogen for normal development of oocytes in ovaries. Antagonism (antagonistic effect): one hormone opposes the action of another hormone. Eg. Insulin and glucagon.

  21. Endocrine dysfunction • Decrease in hormone activity • Decrease in hormone secretion by the endocrine gland (hyposecretion). • Increase removal of the hormone from the blood • Abnormal tissue responsiveness to the hormone:- • Lack of target cell receptors. • Lack of an enzyme essential to the target cell response

  22. Increase in hormone activity • Increase in hormone secretion by the endocrine gland (hypersecretion) • Reduced plasma protein binding of the hormone (too much free, biologically active hormone • Decreased removal of the hormone from the blood:- • Decreased inactivation. • Decreased excretion

  23. Location of endocrine glands

  24. Hypothalamus and pituitary gland Anterior pituitary Hypophyseal portal system

  25. Posterior Pituitary Hypothalamohypophyseal tract

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