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The Endocrine System

The Endocrine System. Endocrine System. Function: Regulates Coordinates Integrates Works cooperatively with the nervous system No ducts: Reactions not immediate -last longer than N.S. responses. Hormones.

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The Endocrine System

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  1. The Endocrine System

  2. Endocrine System • Function: • Regulates • Coordinates • Integrates • Works cooperatively with the nervous system • No ducts: • Reactions not immediate -last longer than N.S. responses

  3. Hormones • Substances secreted by cells that regulate the activity of another tissue or organ • Most produced by glands • Some produced by clusters of cells • Some produced by neurons (neurohormones)

  4. Hormones • Types of Hormones • Amino Acid Derivatives • Simple amines, thyroxin, peptides and proteins • Examples: • Thyroid hormones, epinephrine and NE, insulin, glucagon • Most hormones this type

  5. Hormones • Types of hormones • Steroid hormones • Derived from cholesterol • Includes gonadal hormones (sex hormones) and adrenal hormones (cortex only) • Examples: • Progesterone, testosterone, cortisol, aldosterone

  6. Hormones • Types of hormones • Eicosanoids • Are paracrine hormones (local hormone = produced by cells and released to effect cells in the same area) • Examples: • Prostaglandins, leukotrines

  7. Intracellular Receptors

  8. Receptors • On the target cell -bind hormone • Determine the effect the hormone will have on the target cell • Binding may cause: • Change in membrane permeability or potential • Synthesis of substances such as proteins or enzymes • Activation or deactivation of enzymes • Secretion of substances • Stimulation of mitosis

  9. Hormone Actions • Alter the activity of target cells • Decrease or increase cellular activity in target cells • Only affect cells with receptors for that hormone

  10. Hormone action: What happens when a hormone binds with a receptor? • Channels • 2nd messenger • Genes

  11. HORMONE ACTION Where are the receptors? • On the cell membrane (AA hormones) intracellular second messenger • In the nucleus (steroid hormones & thyroxine) direct gene activation

  12. HORMONE ACTION-Second Messenger Intracellular second messenger • Hormone • Receptor • G protein • Adenylate cyclase system • Cyclic AMP • Protein kinases

  13. Hormone Mechanisms • Second Messengers • Hormone binds to a receptor on plasma membrane • Series of reactions initiated within the cell • Example: • Cyclic AMP

  14. Second Messengers • Cyclic AMP (cAMP) • Formed from ATP when a hormone binds to receptor • Hormone/receptor binding • ‘G’ protein activates or inhibits adenyl cyclase • ATP converted to cAMP • May activate protein kinases • Initiates cascade of enzymes within the cell • Effect depends upon target cell

  15. Second Messenger System

  16. Second Messengers • PIP Mechanism • PIP2 split into diacylglycerol and IP3 • Both act as second messengers • IP3 triggers the release of calcium from the ER • Ca2+ acts as a third messenger • Diacylglycerol may activate protein kinases

  17. Second messenger system

  18. Direct Activation of Genes • Steroid hormones can pass through the plasma membrane • Bind to receptors inside cell • Hormone/receptor binding stimulates genes on the DNA to begin protein production

  19. Gene Activation

  20. Hormone Regulation • Nervous System • Ultimate control of hormone mechanisms belongs to the nervous system • Mainly hypothalamus and sympathetic nervous system

  21. Endocrine Gland Stimuli

  22. Hormone Regulation • Stimulation or inhibition of endocrine glands comes from THREE sources: • Other hormones • Humoral stimuli • Neural stimuli

  23. Hormone Regulation • Hormonal Regulation (by other Hormones) • Hormones may stimulate or inhibit the release of other hormones • Hypothalamus- • Regulates anterior pituitary gland • Pituitary hormones- • Stimulate release of hormones from other glands

  24. Hormone Regulation • Regulation by Humoral Stimuli • Changing ion or nutrient levels in the blood may inhibit or stimulate the release of hormones • Example: • Low blood calcium (Ca2+) • PTH released from the parathyroid glands • Ca2+ released from bone • Increase in blood Ca2+

  25. Hormone Regulation • Regulation by Neural Stimuli • Nerve impulses may stimulate the release of hormones • Example: • Sympathetic neurons stimulate release of epinephrine and norepinephrine from the adrenal medulla

  26. Feedback Mechanisms • Negative Feedback System • Rising hormone or ion levels inhibit further hormone release from the gland • Positive Feedback System • Rising hormone levels cause an increase in the hormone being secreted

  27. Hypo or Hypersecretion • May result in a disorder • Examples: • Diabetes • Grave’s disease • Addison’s disease • Cushing’s disease

  28. Major Endocrine Glands • Pituitary Gland(Hypophysis) • Posterior lobe (Neurohypophysis) • Releases 2 hormones produced in the hypothalamus posterior lobe anterior lobe

  29. Posterior Pituitary Gland • Posterior Lobe • Derived from hypothalamus • Posterior lobe + infundibulum = neurohypophysis • Neuron axons to pituitary = hypothalamic hypophyseal tract hypothalamic hypophyseal tract

  30. Posterior Pituitary Gland • Two hormones released here • Both produced in nuclei of the hypothalamus • Both secreted into capillaries in posterior pituitary for distribution to the body Oxytocin & ADH

  31. Hypothalamus • SON/PVN – produce ADH & oxytocin • Released from posterior pituitary

  32. Pituitary • Posterior lobe: • Pituicytes • ADH • Oxytocin

  33. Posterior Pituitary Gland Paraventricular nuclei • Supraoptic Nucleus • ADH (Vasopressin) • Stimulates increased reabsorption of water by kidney tubules • Decreases urine volume • Increases blood volume • React to Osmoreceptors Supraoptic nuclei • Paraventricular Nucleus • Oxytocin • Uterine contractions • Milk release (Contraction of mammary gland smooth muscle ADH & oxytocin

  34. Ventral Hypothalamus • Releasing and inhibiting hormones • Thru portal system • Target = anterior pituitary

  35. Anterior Pituitary Gland • Hypophyseal Portal System neurons in ventral hypothalamus primary capillary plexus hypophyseal portal veins secondary capillary plexus secretory cells

  36. Anterior Pituitary Gland Ventral hypothalamus • Anterior Lobe = Adenohypophysis • Derived from roof of mouth • Produces hormones • Release of hormones is controlled by hormones from neurons of the ventral hypothalamus = releasing or inhibiting hormones anterior lobe

  37. Pituitary (Hypophysis) • Location and relationships • Densely packed cells (anterior) • Anterior lobe: • TSH • ACTH • FSH • LH • GnRH • Growth h. • Prolactin • MSH

  38. Anterior Pituitary Gland • The following four anterior pituitary hormones are tropic hormones • Tropic Hormones: • TSH • ACTH • FSH • LH

  39. Tropic Hormones • Hormones Secreted • Thyroid Stimulating Hormone (TSH) • Stimulates production and release of thyroid hormones by the thyroid gland • Release stimulated by TRH • Inhibited by rising blood levels of thyroid hormone

  40. Tropic Hormones • Hormones Secreted • Adrenocorticotropic Hormone (ACTH or Corticotropin) • Stimulates secretion of corticosteroid hormones (esp. cortisol) from the adrenal cortex • Release stimulated by CRH, fever, hypoglycemia and stress • Inhibited by rising cortisol levels

  41. Tropic Hormones • Hormones Secreted • Follicle Stimulating Hormone (FSH) • Not present until puberty • Stimulates gamete production and maturation in both males and females • Release stimulated by GnRH • Inhibited by rising gonadal hormones

  42. Anterior Pituitary Gland • Hormones Secreted • Luteinizing Hormone (LH) • Promotes production of gonadal hormones • Controlled by the same hormones as FSH • Triggers ovulation in females

  43. Non-tropic Hormones • Hormones Secreted • Growth Hormone (GH) or Somatotropin • Produced in response to growth hormone releasing hormone (GHRH from hypothalamus) • Also secreted in response to hypoglycemia or decreased blood GH or Increased amino acid levels • Inhibited by GHIH (somatostatin from hypothalamus) • Stimulates cell growth and division in most cells (esp. bone and muscle) • Mobilizes fat to conserve glucose • Hyposecretion results in pituitary dwarfism • Hypersecretion results in gigantism or acromegaly

  44. Non-tropic Hormones • Hormones Secreted • Prolactin (PRL) • Release stimulated by PRH • Inhibited by PIH (dopamine) • Both are influenced by estrogen • Stimulates milk production by breasts

  45. Thyroid Gland - Anatomy

  46. The Thyroid Gland • Two lateral lobes • Composed of follicles • Cuboidal follicle cells produce thyroglobulin • Thyroglobulin stored in lumen of follicle • Iodine attaches • Molecule is split into T3 and T4 (mostly T4) • Hormones enter circulation, more T3 formed thyroid gland

  47. Thyroid Gland - histology • Follicular cells follicles colloid thyroglobulin T3 – triiodothyronine T4 – thyroxine • Parafollicular cells Calcitonin

  48. Thyroid Gland - hormones • Follicular cells thyroglobulin T3 – triiodothyronine T4 – thyroxine • + BMR (glucose oxidation) • maintains bp • tissue growth & development • Parafollicular cells Calcitonin • decreases blood calcium • + osteoblasts

  49. Thyroid Gland – T3/T4 production • Follicles – colloid, follicular cells • Cells make thyroglobulin • Thyroglobulin moves into follicle • Iodine pumped into follicle • Iodine used to make subunits • 1 OR 2 IODINE • Subunits moved into follicle cells • Subunits join to make T3 or T4 • T3/T4 released from follicle cells

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