endocrine glands

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  • 1.Endocrine Glands & Their Functions Anatomy & Physiology II Georgia Perimeter College K. Donaldson, Instructor

2. Endocrine Glands

  • The body contains two kinds of glands:endocrine and exocrine
  • Exocrine Glands: (sudoriferous, sebaceous, and digestive) secrete their products through ducts into body cavities or onto body surfaces.
  • Endocrine Glands:Secrete their products (hormones) into the extracellular spaces around the secretory cells, rather than into ducts.The secretion then diffuses into capillaries and is carried away by the blood.

3. Endocrine Glands

  • The endocrine system consists of endocrine glands and several organs that contain endocrine tissue.
  • The science concerned with the structure and functions of the endocrine glands and the diagnosis and treatment of disorders of the endocrine system is called endocrinology.

4. Comparison of Nervous & Endocrine Systems

  • Together the nervous and endocrine systems coordinate functions of all body systems.
  • The nervous system controls homeostasis through nerve impulses (action potentials) conducted along axons of neurons.
  • In contrast, the endocrine system releases its messenger molecules called hormones into the bloodstream.The circulating blood then delivers hormones to virtually all cells throughout the body.
  • Certain parts of the nervous system stimulate or inhibit the release of hormones.Hormones in turn may promote or inhibit the generation of nerve impulses.

5. Comparison of Nervous and Endocrine Systems

  • Certain parts of the nervous system causes muscles to contract and glands to secrete; the endocrine system. Hormones, in turn, may promote or inhibit the generation of nerve impulses.
  • The nervous system causes muscles to contract and glands to secrete the endocrine system affects virtually all body tissues, altering metabolic activities, regulating growth and development and guiding reproductive processes.
  • Nerve impulses are generally much more rapid in producing their effectsthan are hormones; the effects of the nervous system are also quite brief compared with those of the endocrine system.

6. Overview of Hormone Effects

  • Hormones regulate the internal environment, metabolism, and energy balance.
  • They also help regulate smooth and cardiac muscular contraction, glandular secretion and certain immune responses.
  • Hormones play a role in the integration of growth and development, the maintenance of homeostasis despite emergency environmental disruptions and contribute to the basic processes of reproduction.

7. Hormones

  • Hormones only affect specific target cells that have receptors to recognize a given hormone.
  • Receptors, like other cellular proteins are constantly synthesized and broken down.
  • When a hormone (or neurotransmitter) is present inexcess ,the number ofreceptors may decrease(down regulation) therebydecreasing the responsivenessof target cells to the hormone.

8. Hormones

  • When a hormone (or neurotransmitter) isdeficient , the number ofreceptors may increase (up-regulation ), making the target tissuemore sensitiveto the stimulating effect of the hormone.
  • Hormones that pass into the blood to act on distant target cells are calledcirculating hormones or endocrines.
  • Hormones that act on target cells close to their site of release are calledlocal hormones or paracrines or autocrines.

9. Hormones

  • Chemically, hormones are classified as steroids, biogenic amines, proteins and peptides and eicosanoids.
  • Eicosanoids include prostaglandins and leukotrienes.
  • Water soluble hormones circulate in free form in the blood; lipid soluble steroid and thyroid hormones are carried attached to transport proteins.

10. Mechanisms of Hormone Action

  • The response to a hormone depends on both the hormone and the target cell; various target cells respond differently to the same hormone.

11. Mechanisms of Hormone Action

  • Hormones bind to and activate their specific receptors in two quite different ways.
  • Steroid hormones and thyroid affect cell function by binding to and activating an intracellular receptor (usually in the nucleus), consequently altering gene expression.

12. Mechanisms of Hormone Action

  • Water-soluble hormones alter cell function by activating plasma membrane receptors, which initiate a cascade of events inside the cell.
  • After a water-soluble hormone is released from an endocrine gland, it circulates in the blood, reaches a target cell, and brings a specific message to that cell; since such a hormone can deliver its message only to the plasma membrane, it is a called thefirst messenger.

13. Mechanisms of Hormone Action

  • A second messenger is needed to relay the message inside the cell where hormone-stimulated responses can take place; the best known second messenger is cyclic AMP (cAMP) but other substances are known second messengers.
  • G-Proteins are a common feature of the most second messenger systems; the symptoms of cholera are a direct result of the cholera toxin on G-Proteins in the intestinal lining.

14. Mechanisms of Hormone Action

  • Cyclic AMP does not directly produce a particular physiological response, but instead activates one or more enzymes known as protein kinases.
  • The responsiveness of a target cell to a hormone depends on the hormones concentration and the number of receptors.The manner in which hormones interact with other hormones is also important.

15. Circulating and Local Hormones

  • Hormones that travel in blood and act on distant target cells are calledcirculating hormonesorendocrines .
  • Hormones that act locally without first entering the blood stream are calledlocal hormones .
  • Those that act on neighboring cells are calledparacrines .
  • Those that act on the same cell that secreted them are termedautocrines .

16. Chemical Classes of Hormones

  • Lipid-soluble hormonesinclude the steroids, thyroid hormones, and nitric oxide, which acts as a local hormone in several tissues.
  • Water-soluble hormonesinclude the amines; peptides, proteins, and glycoproteins; and eicosanoids.

17. Hormone Transport In Blood

  • Most water-soluble hormones circulate in plasma in a free, unattached form.
  • Most lipid-soluble hormones bind totransport proteinsto be carried in blood.
  • The transport proteins improve the transportability of lipid-soluble hormones by making them temporarily water-soluble, retard passage of the small hormone molecules through the kidney filter thus slowing the rate of hormone loss in urine, and provide a ready reserve of hormone already present in blood.
  • Protein and peptide hormones, such as insulin, will be destroyed by digestive enzymes and must be given by injection.

18. Mechanisms of Hormone Action

  • The response to a hormone depends on both the hormone and the target cell; various target cells respond differently to different hormones.
  • Actions of Lipid-Soluble Hormones
  • Lipid-soluble hormonesbind to and activate receptors within cells.
  • The activated receptors then alter gene expression which results in the formation of new proteins.
  • The new proteins alter the cells activity and result in the physiological responses of those hormones.

19. Mechanisms of Hormone Action

  • Action of Water-Soluble Hormones
  • Water-soluble hormonesalter cell functions by activating plasma membrane receptors, which set off a cascade of events inside the cell.
  • The water-soluble hormone that binds to the cell membrane receptor is thefirst messenger .
  • Asecond messengeris released inside the cell where hormone stimulated response takes place.
  • A typical mechanism of action of a water-soluble hormone is using cyclic AMP as the second messenger.
  • The hormone binds to the membrane receptor.
  • The activated receptor activates a membraneG-proteinwhich turns onadenylate cyclase .
  • Adenylate cyclaseconverts ATP intocyclic AMPwhich activatesprotein kinases .
  • Protein kinasesphosphorylate enzymes which catalyze reactions that produce the physiological response.
  • Since hormones that bond to plasma membrane receptors initiate a cascade of events, they can induce their effects at very low concentrations.
  • The cholera toxin modifies G-proteins in epithelial cells lining the intestine so they become locked in an activated state which results in the massive fluid loss this toxin causes.

20. Mechanisms of Hormone Action

  • Hormonal Interactions
  • The responsiveness of a target cell to a hormone depends on the hormones concentration, the abundance of the target cells hormone receptors, and influences exerted by other hormones.
  • Three hormonal interactions are thepermissive effect , thesynergistic effect , and theantagonist effect .

21. Hormone Interactions

  • The responsiveness of a target cell to a hormone depends on


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