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A&pi ichapter17


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A&pi ichapter17

  1. 1. Chapter 17: Functional Organization of the Endocrine System
  2. 2. Principles of Chemical Communication• Chemical Messengers – Allow cells to communicate with each other to regulate activities – 4 classes of chemical messengers based on the source of the chemical messenger and its mode of transport in the body • Autocrine chemical messengers • Paracrine chemical messengers • Neurotransmitters • Endocrine chemical messengers
  3. 3. Characteristics of the Endocrine System• Composed of endocrine glands and specialized endocrine cells located throughout the body• Secrete minute amounts of chemical messengers (hormones) into the bloodstream• Hormones travel a distance from their source through the bloodstream to specific sites (target tissues or effectors)
  4. 4. Comparison of the Nervous System and Endocrine Systems• Nervous system and the endocrine system regulate and coordinate the activities of essentially all body structures to achieve and maintain homeostasis – Nervous system functions as a communication system – Endocrine system sends information to the cells it controls in the form of hormones, which are carried by the bloodstream to all parts of the body
  5. 5. Similarities• Structures associated with the brain – E.g. hypothalamus• Same molecule is a neurotransmitter for the nervous system and a hormone for the endocrine system – E.g. epinephrine• Work together to regulate critical body processes – E.g epinephrine
  6. 6. Similarities cont.• Some neurons secrete hormones – Neuropeptides (neurohormones) – E.g. oxytocin
  7. 7. Differences• Mode of transport – Endocrine system secretes hormones which are transported in the bloodstream – Nervous system secretes neurotransmitters which are released directly onto their target cells• Speed of response – Nervous system responds faster than the endocrine
  8. 8. Differences cont.• Duration of response – Nervous system activates its targets quickly – Endocrine system tends to have longer-lasting effects
  9. 9. Hormones• Characteristics – Stability • Life span of hormone varies with its chemical nature • Expressed as half-life – amount of time it takes for 50% of the circulating hormone to be removed from the circulation and excreted – Communication • Able to regulate specific cellular pathways once they arrive at their targets – Distribution • Transported by the blood to many locations
  10. 10. Chemical Nature of Hormones• Lipid soluble – Steroid hormones, thyroid hormones and fatty acid derivative hormones – Travel in bloodstream bound to binding proteins• Water soluble – Protein hormones, peptide hormones and most amino acid derivative hormone – Circulate as free hormones – Relatively short half-lives
  11. 11. Patterns of Hormone Secretion• 3 main patterns of hormone secretion – Chronic hormone secretion – Acute hormone secretion – Episodic hormone secretion • Steroid reproductive hormones
  12. 12. Control of Hormone Secretion• 3 types of stimuli regulate hormone release – Humoral • Blood-borne molecules can directly stimulate the release of some hormones – Neural • Involves neural stimuli of endocrine glands – Hormonal • Hormone is secreted that stimulates the secretion of other hormones
  13. 13. Control by Humoral Stimuli
  14. 14. Control by Neural Stimuli
  15. 15. Control by Hormonal Stimuli
  16. 16. Regulation of Hormone Levels in the Blood• 2 major mechanisms – Negative feedback • Most hormones are regulated
  17. 17. • Positive feedback – Example:
  18. 18. Hormone Receptors and Mechanisms of Action• Hormones exert their actions by binding to proteins called receptors – Only can stimulate cells that have the receptor for that hormone – Specific
  19. 19. • Down regulation• Up regulation
  20. 20. Classes of Receptors• Lipid-soluble hormones bind to nuclear receptors – Relatively small – Able to diffuse through the plasma membrane and bind to nuclear receptors
  21. 21. • Water-soluble hormones bind to membrane- bound receptors – Large molecules and cannot pass through the plasma membrane – Interact with membrane-bound receptors
  22. 22. Action of Nuclear Receptors
  23. 23. Membrane-Bound Receptors and Signal Amplification• Membrane-bound receptors activate responses in 2-ways – Receptors may alter the activity of G proteins at the inner surface of the plasma membrane – Receptors may directly alter the activity of intracellular enzymes – Second messenger system
  24. 24. Receptors that activate G Proteins• G proteins – 3 subunits • Alpha, beta and gamma • Guanine nucleotide bound to alpha subunit – Inactive state – GDP bound – Active state – GTP bound
  25. 25. G proteins that Interact with Adenylate Cyclase
  26. 26. G Proteins that Activate other Intracellular Mediators• Alter the concentration of intracellular mediators other than Ca2+ or cAMP
  27. 27. Receptors that Directly Activate Intracellular Mediators
  28. 28. Receptors that Phosphorylate Intracellular Proteins • Hormones bind to membrane-bound receptors. • Part of receptor protein on inside of membrane acts as an enzyme to phosphorylate proteins • E.g., insulin receptors bound to insulin cause phosphorylation of proteins and cell responds to presence of insulin.
  29. 29. Signal Amplification