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Endocrine System

Endocrine System. Chapter 16. Overview. Overall goal of endocrine system: maintain a stable internal environment ( homeostasis ) Endocrine glands are “ ductless glands ” Endocrine glands secrete hormones which travel through the blood to a target cell

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Endocrine System

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  1. Endocrine System Chapter 16

  2. Overview • Overall goal of endocrine system: maintain a stable internal environment (homeostasis) • Endocrine glands are “ductless glands” • Endocrine glands secrete hormones which travel through the blood to a target cell • Receptor must be present on target cell

  3. Endocrine vs Nervous System • Both systems function to maintain homeostasis • Main differences:

  4. Endocrine vs Nervous System

  5. Major Endocrine Glands

  6. Classification of Hormones • Classified by Function • Tropic hormones: target other endocrine glands and stimulate their growth & secretion • Sex hormones: target reproductive tissues • Anabolic hormones: stimulate anabolism in their target cell

  7. Chemical Classifications of Hormones

  8. How Hormones Work • Hormones bind to receptors on target cells • Lock & key • Hormone-receptor interactions produce regulatory changes within the target cell • Ex: initiating protein synthesis; activation/inactivation of enzymes; opening/closing of ion channels

  9. How Hormones Work • Synergism: combinations of hormones have a greater effect on the target cell compared to a single hormone acting alone • Permissiveness: a small amount of one hormone allows a second hormone to exhibit its full effect on the target cell • Antagonism: two hormones produce opposite effects

  10. Regulation of Hormone Secretion • Hormone secretion is controlled by a negative feedback loop • Ex: parathyroid hormone (PTH) and blood calcium levels (fig 16-10) • Ex: insulin and blood glucose levels

  11. Endocrine Feedback Loop

  12. Hyper vs Hyposecretion • Tumors or abnormalities of the endocrine glands cause secretion of too much or too little hormone • Hypersecretion: production of too much hormone • Hyposecretion: production of too little hormone • Results in lack of target cell response • Also caused by target cell insensitivity

  13. Pituitary Gland • Also called hypophysis • Located on ventral surface of brain, inferior to the hypothalamus • “Master gland” because functions are crucial to life • Composed of two parts: Anterior Pituitary and Posterior Pituitary

  14. Anterior Pituitary • Hormones secreted from Anterior Pituitary: • Growth Hormone • Prolactin • Trophic hormones • Thyroid-stimulating hormone (TSH) • Adrenocorticotropic hormone (ACTH) • Gonadotropic hormones • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH)

  15. Growth Hormone • Growth Hormone (GH) – promotes growth by stimulating protein anabolism • Increased protein anabolism allows increased growth rate • Target cells: • Promotes growth of bone and muscle • GH has a hyperglycemic effect; antagonist of insulin • Hyperglycemic effect because GH stimulates fat metabolism • Interaction vital to maintaining homeostasis of blood glucose levels

  16. Growth Hormone Abnormalities • Hypersecretion • Prior to ossification of the epiphyseal plates hypersections of GH results in rapid skeletal growth  Gigantism • After closure of epiphyseal plates hypersecretion causes cartilage to continue to form new bone  Acromegaly • Distorted appearance; enlarged hands, feet, face, jaw; thickened skin

  17. Growth Hormone Abnormalities • Hyposecretion • Results in stunted body growth  pituitary dwarfism • Treated with genetically engineered growth hormone

  18. Prolactin (PRL) • Also called lactogenic hormone • Initiates milk secretion (lactation) • Target cells: Mammary glands • During pregnancy PRL promotes development of breasts • At birth PRL stimulates milk production

  19. Prolactin Abnormalities • Hypersecretion: • Lactation in non-nursing women • Disruption of menstrual cycle • Impotence in men • Hyposecretion: • Insignificant unless mother wishes to breastfeed

  20. Trophic Hormones • Review: a trophic hormone stimulate effects of other endocrine glands • Trophic hormones released from anterior pituitary gland: • Thyroid-stimulating hormone (TSH) • Adrenocorticotropic hormone (ACTH) • Gonadotrophic hormones • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH)

  21. Thyroid-stimulating hormone (TSH) • Promotes and maintains growth and development of thyroid gland • Required for thyroid gland to secrete its hormones

  22. Adrenocorticotropic hormone (ACTH) • Promotes and maintains normal growth and development of the cortex (outer portion) of the adrenal gland • Required for adrenal cortex to secrete its hormone

  23. Gonadotrophic hormones • Target cells: gonads (testes & ovaries) • Follicle-stimulating hormone (FSH) • Females: • Stimulates growth & development of an ovum that is released each month during ovulation • Stimulate estrogen release from the ovaries • Males • Stimulates development of seminiferous tubules and maintains sperm production in the testes

  24. Gonadotrophic hormones • Luteinizing hormone (LH) • Females: • Triggers ovulation • Promotes development of corpus luteum which secretes progesterone and estrogen; these hormones help maintain pregnancy • Males: • Stimulates cells of the testes to synthesize and secrete testosterone

  25. Control of Anterior Pituitary Secretion • The hypothalamus releases chemical called releasing hormones which influence hormone secretion from the anterior pituitary gland • This regulatory mechanism is a negative feedback loop

  26. Posterior Pituitary • Hormones secreted from Posterior Pituitary: • Antidiuretic Hormone (ADH) • Oxytocin (OH)

  27. Antidiuretic Hormone (ADH) • Target cells: kidney • Prevents formation of large volumes of dilute urine • Antidiuresis • Helps conserve water balance • Example: • Blood is hypertonic  change detected by osmoreceptors  ADH is released  water reabsorbed in kidneys and returned to blood

  28. ADH Abnormalities • Hyposecretion • Diabetes insipidus • Increased urine output of dilute urine • “high and dry” • Na+ levels are increased; ICF dehydrated • Hypersecretion • Syndrome of inappropriate antidiuretic hormone (SIADH) • Decreased urine output • Fluid overload; low Na+ levels

  29. Oxytocin (OT) • Target cells: mammary glands & uterine smooth muscle • Operates on a positive feedback loop • Stimulates uterine smooth muscle contractions • During childbirth stretching of receptors causes continued release of oxytocin until after delivery of the placenta • Ejection of milk into ducts of the breast of lactating women • When breastfeeding the suckling action of the baby causes secretion of additional oxytocin increasing milk production • Breastfeeding also helps the uterus continue to contract back to normal size during the postpartum period

  30. Pineal Body • Regulates the body’s biological clock • Patterns of eating • Sleeping • Female reproductive cycle • Behavior • Secretes melatonin • Induces sleep • Secretion is inhibited by sunlight • Target cell in humans is unknown

  31. Melatonin & Seasonal Affective Disorder • Also know as “winter depression” • During shorter days, melatonin secretion increases causes a depressed feeling in affected patients • Treatment • Exposure to high-intensity lights to inhibit melatonin secretion

  32. Thyroid Gland • The thyroid gland is composed of two lateral lobes connected by an isthmus • Located on the anterior and lateral surfaces of the trachea, below the larynx

  33. Thyroid Hormones • Tetraiodothyronine or thyroxine (T4) • Most abundant thyroid hormone • Contains 4 iodine atoms • May have effect on target cells, but mostly serve as precursor to T3 • Triodothyronine (T3) • “principal thyroid hormone” • Contains 3 iodine atoms

  34. Thyroid Hormones • Both hormone bind to plasma proteins once secreted into the bloodstream • Function: • Regulate metabolic rate of all cells • Regulate cell growth • Regulate tissue differentiation • Target cells: “general” because thyroid hormones can potentially interact with all cells of the body

  35. Hypersection • Graves Disease • Autoimmune condition (thyroid stimulating antibodies causes abnormal secretion) • Weight loss • Increases basal metabolic rate • Increased heart and respiratory rate • exophthalmos

  36. Exophthalmos

  37. Hyposecretion of Thyroid Hormone • Cretinism – develops during the growth years due to hypothyroidism • Low metabolic rate • Retarded growth and sexual development • Mental retardation (possibly) • Hypothyroidism later in life • Decreased metabolic rate • Loss of mental & physical vigor • Weight gain • Loss of hair • Yellow discoloration of the skin • myxedema

  38. Goiter • Caused by lack of iodine in the diet • Iodine is needed to synthesize thyroid hormone • Lack of iodine causes drop in thyroid hormone production/secretion • Negative feedback loop informs hypothalamus and anterior pituitary to release releasing hormones and TSH • Lack of iodine causes enlargement of thyroid gland

  39. Calcitonin • The 3rd hormone secreted from the thyroid gland • Target cells – bone • Function – regulates calcium levels in the blood by decreasing blood calcium levels • Increases action of osteoblasts (build bone) and inhibits action of osteoclasts (breakdown bone) • Antagonist to parathyroid hormone

  40. Parathyroid Glands • Parathyroid glands are embedded in the posterior aspect of the thyroid glands • Usually 4 or 5 parathyroid glands

  41. Parathyroid Hormone • Secreted from Parathyroid glands • Target cells: bone and kidney • Action: maintains calcium homeostasis • Increases osteoclast activity; decrease osteoblast activity • Calcium absorbed in kidneys and returned to the bloodstream • Activates vitamin D in the kidneys which increases intestinal absorption of calcium • Parathyroid hormone is an antagonist to calcitonin

  42. Adrenal Glands • Located on top of both of the kidneys • Composed of two parts: • Outer portion  adrenal cortex • Inner portion  adrenal medulla • Both parts of the adrenal glands are structurally and functionally different; often treated as two different glands

  43. Adrenal Cortex • Composed of three distinct layers or zones • Outer zone  secrete mineralocorticoids • Middle zone  secrete glucocorticoids • Inner zone  secrete glucocorticoids and gonadocorticoids

  44. Pancreas • Located in the LUQ • Contains both endocrine and exocrine tissue • Endocrine portion is made up of tiny islands of cells called pancreatic islets (also islets of Langerhans) • Alpha cells secrete glucagon • Beta cells secrete insulin

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