Principles of endocrine regulation

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The active principles of the endocrine glands are called hormones.
Hormones are specific chemical substances discharged directly into the blood.
The blood distributes the hormones through out the body.

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Principles of endocrine regulation

  1. 1.           Introduction Coordinating systems of human body. Science of Endocrinology Endocrine glands. What is a hormone? Salient features. Chemical classes of hormones Mechanism of hormone action Hormone transport Hormone receptors Endocrine disrupting chemicals.
  2. 2. Central nervous system Nervous coordination Coordinating Peripheral nervous system Autonomic nervous system Systems in animals Chemical Endocrine coordination system
  3. 3. Neuroendocrine system Nervous system Endocrine system Functional interrelationship Regulating the rate Maintaining the constancy of Of physiological processes Internal environment Dual role of nerve cells Conduction of nerve impulses – as neurons Secretion of neuro-humors - as endocrine cells
  4. 4. The science dealing with the chemical integration of the physiological functions of an organism.  The science of Endocrinology was born through the experiments of Bayliss and Starling(1902 to 1905).  Pende introduced the term ‘Endocrinology’ (Greek, endon=within; krinein= to separate). 
  5. 5. Exocrine glands or glands with duct or Glands of external secretion e.g. salivary glands Endocrine glands or ductless glands or Glands of internal secretion e.g. pituitary gland
  6. 6. The active principles of the endocrine glands are called hormones.  Hormones are specific chemical substances discharged directly into the blood.  The blood distributes the hormones through out the body.  But hormones produce specific physiological effect on certain target organs. 
  7. 7. A hormone is a regulatory chemical that is secreted into the blood by an endocrine gland. •The word hormone is derived from the Greek word ‘hormon’ which means ‘to excite’.Bayliss and Starling in 1905 coined the term’ hormone’.
  8. 8. Hormones-products of endocrine glands Neuro-hormones – products of nerve cells and released at neurohemal organ Neurohumorsproducts of nerve cells and released at axons Parahormonesproducts of dead or injured tissue e.g. histomine Phytohormones – plant hormones e.g.auxin Pheromones ectohormones
  9. 9. Hormones are low molecular weight chemical messengers.  They are secreted in trace amounts in response to specific secretary stimuli .  They are soluble in water and act as catalysts.  A single hormone have multiple effects on a single target tissue or on several different tissues. 
  10. 10. Hormones have high degree of action specificity.  They are not species specific and nonantigenic.  They are inactivated as soon as their functions are over.  Endocrine glands are under the control of nerves. 
  11. 11. Amines • Secreted by gland cells of nervous origin. • Adrenaline, ADH Steroids • Secreted by glands derived from coelomic mesothelium. • Corticosteroids, estrogens, androgens Proteins • Hormones made up of amino acids and polypeptides. • Thyroxine, calcitonin, STH
  12. 12. Steroid hormones are formed from cholesterol.  They are lipid-soluble hydrophobic molecules.  They are secreted by the gonads, adrenal cortex and placenta.  E.g. aldosterone, cotisol, estrogen, testostero ne and progesterone. 
  13. 13. Peptide hormones are short chains of amino acids.  They are water-soluble.  They are secreted by pituitary and parathyroid glands.  E.g. oxytocin, vasopressin, calcitonin, insulin 
  14. 14. They are derived from the amino acid tyrosine.  They are secreted from the thyroid and the adrenal medulla. 
  15. 15. Hormones affect intracellular enzyme systems • Hormones activate or inhibit enzyme systems e.g phosporylase Hormones alter cellular activities • Insulin promote transfer of glucose Hormones directly activate or suppress particular genes • Ecdysone causes puffing of certain genes
  16. 16. Humoral signal-secretion depend upon the level of blood ions and nutrients. E.g. insulin production controlled by blood glucose.  Neuronal signal- secretion depend on nerve impulses-stimulation of symphathetic nervous system release catecholamines  Hormonal signal- some hormones control the release of hormones from another endocrine tissue-hypothalamus hormones. 
  17. 17. Other hormones e.g.trophic hormones Plasma concentrations of ions /nutrients Neurons & mental activity Environmental changes e.g. light, temperature
  18. 18. The production of a hormone by an endocrine gland is controlled by its circulatory level.  A reciprocal relationship exists between the blood level of a hormone and rate of its synthesis and secretion.  Feedback mechanisms help in maintaining homeostasis within the endocrine system. 
  19. 19. This concept is proposed by Moore and Price in 1932.  It is a two-way communication between the endocrine gland and the target gland.  It is a self-balancing mechanism. 
  20. 20. In a negative feedback system, a gland is sensitive to the concentration of the substance it regulates.  When the concentration of the regulated substance reaches a certain threshold level, it inhibits the gland from secreting more hormone until the concentration returns to normal. 
  21. 21. Neurons in the hypothalamus secrete thyroid releasing hormone (TRH), which stimulates the anterior pituitary to secrete thyroidstimulating hormone (TSH).  TSH stimulates the synthesis and secretion of thyroid hormones.  When blood levels of thyroid hormones increase above a certain threshold, TRHsecreting neurons in the hypothalamus are inhibited and stop secreting TRH. This is an example of "negative feedback". 
  22. 22. The increased activity of an endocrine gland is followed by stimulation.  Positive feedback is not common.  E.g. action of oxytocin on uterine muscle during child birth. Loop stops when baby leaves birth canal.  Positive feedback is easily observed under experimental conditions e.g. muscular injection of estrogen in female induces ovulation. 
  23. 23. Hormones are normally present in blood plasma.  Steroid and thyroid hormones bind to transport proteins in the plasma.  Amines and peptide hormones are hydrophilic and mix easily with blood plasma.  Unbound hormones have shorter half life and bound hormones exhibit longer half life. Transport proteins protect circulating hormones. 
  24. 24. Hormones activate only those cells that have receptors for them.  Hormone receptors are located on plasma membrane, in the cytoplasm or in the nucleus.  Hormone – receptor interactions exhibit specificity and saturation.  Protein hormones react with receptors on the surface of the cell. Steroid hormones react with receptor sites inside a cell. 
  25. 25.  The endocrine control of metabolic function can lead to cascade or step-bystep amplification. Hypothalamus Anterior pituitary Adrenal cortex •Corticotrophin RH •0.1μg •Adrenocorticotrophin •1μg •Corticosteroid •40μg •Glycogen deposition •5600μg Liver
  26. 26. Homeostatic function • Regulate body fluid composition • Rate of gaseous exchange • Activity of cardiovascular system Integrative function • Supports the role of nervous system Morphogenetic function • Influences embryonic development Permissive function • Certain hormones require the presence of another hormone for the expression of their activity.
  27. 27. EDCs are both natural or man-made chemicals that may mimic or interfere with the function of hormones in the body.  Environmental endocrine disrupting chemicals include persistent organic pollutants (POPs) such as pesticides (DDT), dioxins, polychlorinated biphenyls(PCBs) and plasticizers (biphenol A) 
  28. 28. Endocrine disruption is an important public health concern.  EDCs produce adverse developmental, reproductive, neurological and immune effects in both humans and wildlife.  In humans, EDCs may cause:      Reduce male fertility Induce abnormalities in male reproductive organs Cause reproductive diseases in females Neuro-developmental disorders in children
  29. 29.      Dr.B.Victor is a highly experienced postgraduate professor, recently retired from the reputed educational institution - St. Xavier’ s College, Palayamkottai, India-627001. He was the dean of sciences and assistant controller of examinations. He has more than 32 years of teaching and research experience He has taught a diversity of courses ranging from pre- university to post graduate classes. Send your comments to : bonfiliusvictor@gmail.com

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