Endocrine Glands

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<ul><li>1.Endocrine Glands &amp; Their Functions Anatomy &amp; Physiology II Georgia Perimeter College K. Donaldson, Instructor</li></ul><p>2. Endocrine Glands </p> <ul><li>The body contains two kinds of glands:endocrine and exocrine </li></ul><ul><li>Exocrine Glands: (sudoriferous, sebaceous, and digestive) secrete their products through ducts into body cavities or onto body surfaces. </li></ul><ul><li>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.</li></ul><p>3. Endocrine Glands </p> <ul><li>The endocrine system consists of endocrine glands and several organs that contain endocrine tissue.</li></ul><ul><li>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. </li></ul><p>4. Comparison of Nervous &amp; Endocrine Systems </p> <ul><li>Together the nervous and endocrine systems coordinate functions of all body systems. </li></ul><ul><li>The nervous system controls homeostasis through nerve impulses (action potentials) conducted along axons of neurons.</li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul><p>5. Comparison of Nervous and Endocrine Systems </p> <ul><li>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. </li></ul><ul><li>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.</li></ul><ul><li>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.</li></ul><p>6. Overview of Hormone Effects </p> <ul><li>Hormones regulate the internal environment, metabolism, and energy balance. </li></ul><ul><li>They also help regulate smooth and cardiac muscular contraction, glandular secretion and certain immune responses. </li></ul><ul><li>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. </li></ul><p>7. Hormones </p> <ul><li>Hormones only affect specific target cells that have receptors to recognize a given hormone. </li></ul><ul><li>Receptors, like other cellular proteins are constantly synthesized and broken down. </li></ul><ul><li>When a hormone (or neurotransmitter) is present inexcess ,the number ofreceptors may decrease(down regulation) therebydecreasing the responsivenessof target cells to the hormone.</li></ul><p>8. Hormones </p> <ul><li>When a hormone (or neurotransmitter) isdeficient , the number ofreceptors may increase (up-regulation ), making the target tissuemore sensitiveto the stimulating effect of the hormone.</li></ul><ul><li>Hormones that pass into the blood to act on distant target cells are calledcirculating hormones or endocrines.</li></ul><ul><li>Hormones that act on target cells close to their site of release are calledlocal hormones or paracrines or autocrines.</li></ul><p>9. Hormones </p> <ul><li>Chemically, hormones are classified as steroids, biogenic amines, proteins and peptides and eicosanoids.</li></ul><ul><li>Eicosanoids include prostaglandins and leukotrienes. </li></ul><ul><li>Water soluble hormones circulate in free form in the blood; lipid soluble steroid and thyroid hormones are carried attached to transport proteins.</li></ul><p>10. Mechanisms of Hormone Action </p> <ul><li>The response to a hormone depends on both the hormone and the target cell; various target cells respond differently to the same hormone.</li></ul><p>11. Mechanisms of Hormone Action </p> <ul><li>Hormones bind to and activate their specific receptors in two quite different ways. </li></ul><ul><li>Steroid hormones and thyroid affect cell function by binding to and activating an intracellular receptor (usually in the nucleus), consequently altering gene expression.</li></ul><p>12. Mechanisms of Hormone Action </p> <ul><li>Water-soluble hormones alter cell function by activating plasma membrane receptors, which initiate a cascade of events inside the cell.</li></ul><ul><li>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. </li></ul><p>13. Mechanisms of Hormone Action </p> <ul><li>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.</li></ul><ul><li>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.</li></ul><p>14. Mechanisms of Hormone Action </p> <ul><li>Cyclic AMP does not directly produce a particular physiological response, but instead activates one or more enzymes known as protein kinases. </li></ul><ul><li>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. </li></ul><p>15. Circulating and Local Hormones </p> <ul><li>Hormones that travel in blood and act on distant target cells are calledcirculating hormonesorendocrines . </li></ul><ul><li>Hormones that act locally without first entering the blood stream are calledlocal hormones . </li></ul><ul><li>Those that act on neighboring cells are calledparacrines . </li></ul><ul><li>Those that act on the same cell that secreted them are termedautocrines . </li></ul><p>16. Chemical Classes of Hormones </p> <ul><li>Lipid-soluble hormonesinclude the steroids, thyroid hormones, and nitric oxide, which acts as a local hormone in several tissues. </li></ul><ul><li>Water-soluble hormonesinclude the amines; peptides, proteins, and glycoproteins; and eicosanoids. </li></ul><p>17. Hormone Transport In Blood </p> <ul><li>Most water-soluble hormones circulate in plasma in a free, unattached form. </li></ul><ul><li>Most lipid-soluble hormones bind totransport proteinsto be carried in blood. </li></ul><ul><li>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. </li></ul><ul><li>Protein and peptide hormones, such as insulin, will be destroyed by digestive enzymes and must be given by injection. </li></ul><p>18. Mechanisms of Hormone Action </p> <ul><li>The response to a hormone depends on both the hormone and the target cell; various target cells respond differently to different hormones. </li></ul><ul><li>Actions of Lipid-Soluble Hormones </li></ul><ul><li>Lipid-soluble hormonesbind to and activate receptors within cells. </li></ul><ul><li>The activated receptors then alter gene expression which results in the formation of new proteins. </li></ul><ul><li>The new proteins alter the cells activity and result in the physiological responses of those hormones. </li></ul><p>19. Mechanisms of Hormone Action </p> <ul><li>Action of Water-Soluble Hormones </li></ul><ul><li>Water-soluble hormonesalter cell functions by activating plasma membrane receptors, which set off a cascade of events inside the cell. </li></ul><ul><li>The water-soluble hormone that binds to the cell membrane receptor is thefirst messenger . </li></ul><ul><li>Asecond messengeris released inside the cell where hormone stimulated response takes place. </li></ul><ul><li>A typical mechanism of action of a water-soluble hormone is using cyclic AMP as the second messenger. </li></ul><ul><li>The hormone binds to the membrane receptor. </li></ul><ul><li>The activated receptor activates a membraneG-proteinwhich turns onadenylate cyclase . </li></ul><ul><li>Adenylate cyclaseconverts ATP intocyclic AMPwhich activatesprotein kinases . </li></ul><ul><li>Protein kinasesphosphorylate enzymes which catalyze reactions that produce the physiological response. </li></ul><ul><li>Since hormones that bond to plasma membrane receptors initiate a cascade of events, they can induce their effects at very low concentrations. </li></ul><ul><li>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.</li></ul><p>20. Mechanisms of Hormone Action </p> <ul><li>Hormonal Interactions </li></ul><ul><li>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. </li></ul><ul><li>Three hormonal interactions are thepermissive effect , thesynergistic effect , and theantagonist effect . </li></ul><p>21. Hormone Interactions </p> <ul><li>The responsiveness of a target cell to a hormone depends on several factors:the hormones concentration, the abundance of the target cells hormone receptors, and the influences exerted by the other hormones.</li></ul><ul><li>A target cell responds more vigorously when the level of a hormone rises or when it has more receptors (up-regulation) .</li></ul><ul><li>In addition, the actions of some hormones on target cells require a simultaneous or recent exposure to a second hormone.The second hormone in this case is said to have a Permissive Effect.</li></ul><p>22. Hormone Interactions </p> <ul><li>Examples of Permissive Effect:Epinephrine alone only weakly stimulates lipolysis (the breakdown of triglycerides) but when small amounts of thyroid hormones (T3 and T4) are present, the same amount of epinephrine stimulates lipolysis much more powerfully. </li></ul><ul><li>Sometimes the permissive hormone increases the number of receptors for the other hormone and sometimes it promotes the synthesis of an enzyme required for the expression of the other hormones effects.</li></ul><p>23. Hormone Interactions </p> <ul><li>When the effect of two hormones acting together is greater or more extensive than the effect of each hormone acting alone, the two hormones are said to have a Synergistic Effect.</li></ul><ul><li>For example, normal development of oocytes in the ovaries requires both follicle-stimulating hormone from the anterior pituitary and estrogens from the ovaries.Neither hormone alone is sufficient. </li></ul><p>24. Hormone Interactions </p> <ul><li>When one hormone opposes the actions of another hormone, the two hormones are said to have Antagonistic Effects.</li></ul><ul><li>An example of antagonistic pair of hormones is insulin which promotes synthesis of glycogen by liver cells and glucagon, which stimulates breakdown of glycogen in the liver.</li></ul><p>25. Control of Hormone Secretions </p> <ul><li>Most hormones are released in short bursts, with little or no release between bursts. Regulation of hormone secretion normally maintains homeostasis and prevents overproduction or underproduction of a particular hormone; when these regulating mechanisms do not operate properly, disorders result. </li></ul><ul><li>Hormone secretion is controlled by signals from the nervous system, by chemical changes in the blood, and by other hormones. </li></ul><ul><li>Most often,negative feedback systemsregulate hormonal secretions. </li></ul><p>26. Hypothalamus &amp; Pituitary Gland </p> <ul><li>Thehypothalamusis the major integrating link between the nervous and endocrine systems. </li></ul><ul><li>The hypothalamus and the pituitary gland (hypophysis) regulate virtually all aspects of growth, development, metabolism, and homeostasis. </li></ul><ul><li>The pituitary gland is located in the sella turcica of the sphenoid bone and is differentiated into theanterior pituitary( adenohypophysis ), theposterior pituitary( neurohypophysis ), andpars intermedia(avascular zone in between). </li></ul><p>27. Anterior Pituitary </p> <ul><li>Anterior Pituitary Gland (Adenohypophysis) </li></ul><ul><li>Hormones of the anterior pituitary are controlled by releasing or inhibiting hormones produced by the hypothalamus. </li></ul><ul><li>The blood supply to the anterior pituitary is from thesuperior hypophyseal arteries . </li></ul><ul><li>Hormones of the anterior pituitary and the cells that produce them are as follows. </li></ul><p>28. Anterior Pituitary </p> <ul><li>Human growth hormone( hGH ) is secreted bysomatotrophs . </li></ul><ul><li>Thyroid-stimulating hormone( TSH ) is secreted bythyrotrophs . </li></ul><ul><li>Follicle-stimulating hormone( FSH ) andluteinizing hormone( LH ) are secreted by gonadotrophs. </li></ul><ul><li>Prolactin( PRL ) is secreted bylactrotrophs . </li></ul><ul><li>Adrenocorticotrophic hormone( ACTH ) andmelanocyte-stimulating hormone( MSH ) are secreted bycorticotrophs . </li></ul><ul><li>Secretion of anterior pituitary gland hormones is regulated byhypothalamic regulating hormonesand bynegative feedbackmechanisms. </li></ul><p>29. Anterior Pituitary </p> <ul><li>Human Growth Hormone and Insulinlike Growth Factors </li></ul><ul><li>Human growth hormone( hGH ) is the most plentiful anterior pituitary hormone. </li></ul><ul><li>It acts indirectly on tissues by promoting the synthesis and secretion of small protein hormones calledinsulinlike growth factors( IGFs ). </li></ul><ul><li>IGFs stimulate general body growth and regulate various aspects of metabolism. </li></ul><ul><li>Various stimuli promote and inhibit hGH production. </li></ul><ul><li>One symptom of excess hGH is hyperglycemia.</li></ul><p>30. Anterior Pituitary Gland </p> <ul><li>Thyroid-stimulating hormone( TSH ) regulates thyroid gland activities and is controlled by TFH (thyrotropin releasing hormone). </li></ul><ul><li>Follicle-Stimulating Hormone( FSH ) </li></ul><ul><li>In females, FSH initiates follicle development and secretion of estrogens in the ovaries. </li></ul><ul><li>In males, FSH stimulates sperm production in the testes. </li></ul><p>31. Anterior Pituitary Gland </p> <ul><li>Luteinizing Hormone( LH ) </li></ul><ul><li>In females, LH stimulates secretion of estrogen by ovarian cells to result in ovulation and stimulates formation of the corpus luteum and secretion of progesterone. </li></ul><ul><li>In males, LH stimulates the interstitial cells of the testes to secrete testosterone. </li></ul><ul><li>Prolactin( PRL ), together with other hormones, initiates and maintains milk secretion by the mammary glands. </li></ul><ul><li>Adrenocorticotrophic hormone( ACTH ) controls the production and secretion of hormones called glucocorticoids by the cortex of the adrenal gland.</li></ul><ul><li>Melanocyte-stimulating hormone( MSH ) increases skin pigmentation although its exact role in humans is unknown. </li></ul><p>32. Posterior Pituitary </p> <ul><li>Posterior Pituitary Gland (Neurohypophysis) </li></ul><ul><li>Although the posterior pituitary gland does not synthesize hormones, it does store and release two hormones. </li></ul><ul><li>The neural connection between the hypothalamus and the neurohypophysis is via thehypothalamohypophyseal tract. </li></ul><ul><li>Hormones made by the hypothalamus and stored in the posterior pituitary areoxytocin( OT ) andantidiuretic hormone( ADH ). </li></ul><p>33. Posterior Pituitary </p> <ul><li>Oxytocinstimulates contraction of the uterus and ejection (let-down) of milk from the breasts.</li></ul><ul><li>Nursing a baby after delivery stiumlates oxytocin release promoting uterine contractions and the expulsion of the placenta (Clinical Application). </li></ul><ul><li>Antidiuretic hormonestimulates water reabsorption by the kidneys and arteriolar constriction. </li></ul><ul><li>The effect of ADH is to decrease urine volume and conserve body water. </li></ul><ul><li>ADH is controlled primarily by osmotic pressure of the blood. </li></ul><p>34. Thyroid Gland </p> <ul><li>Thethyroid glandis located just below the larynx and has right and left lateral lobes (Figure 18.10a). </li></ul><ul><li>Histologically, the thyroid consists of the thyroid follicles composed offollicular cells , which secrete the thyroid hormonesthyroxine( T4 ) andtriiodothyronine( T3 ), andparafo...</li></ul>


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