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Understanding the Endocrine System: Hormones and Functions

Explore the intricate workings of the endocrine system as it regulates, coordinates, and integrates various bodily functions. Learn about different types of hormones, receptor mechanisms, hormone actions, and major endocrine glands.

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Understanding the Endocrine System: Hormones and Functions

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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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