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 Glands of the endocrine system are present throughout the body Most cells are regulated by the endocrine system

3. Endocrine vs Nervous System Both systems function to maintain homeostasis Main differences: FeatureEndocrine SystemNervous System Effector cellsTarget cells throughout the body Postsynaptic cells in muscle and glandular tissue only Chemical messengerHormoneNeurotransmitter Distance traveled by messenger Long – in bloodShort – across synaptic cleft Regulatory effectsSlow to appear; long-lastingAppear rapidly; short

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. Classification of Hormones Classified by Chemical Structure –Steroid Hormones Derived from cholesterol Lipid soluble; can pass through phospholipid bilayer –Nonsteroid Hormones Synthesized from amino acids Proteins, Glycoproteins, peptides, amino acid derivatives (Fig 16-3)

8. Chemical Classifications of Hormones

9. 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 Endocrine glands produce more hormone molecules than necessary to hit the target cells –Excess hormones are excreted in urine or broken down by metabolic processes

10. 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

11. Mechanisms of Steroid Hormone Action Steroids are lipids  not soluble in blood plasma (mostly H 2 O) In blood steroids attach to plasma proteins Steroid reaches a target cell  dissociates from plasma protein  diffuses into target cell In the nucleus a hormone-receptor complex is formed Hormone-receptor complexes in the nucleus trigger protein synthesis (transcription & translation) Increase steroid = increase response (protein synthesis) Regulatory effects of hormones are slow to appear

12. Mechanisms of Steroid Hormone Action

13. Mechanisms of Nonsteriod Hormone Action Nonsteroid hormones operate according to the second messenger hypothesis –Nonsteroid hormone is the “1 st messenger” and binds to a receptor on the plasma membrane of the target cell –The “message” is relayed inside the cell to a “2 nd messenger” which triggers the appropriate cellular response

14. Second Messenger Mechanism 1.Nonsteroid hormone (1 st messenger) binds with receptor on plasma membrane 2.Hormone-receptor complex activates a membrane protein called the G protein 3.G protein activates guanosine triphosphate (GTP) which also activates another membrane protein (adenyl cyclase)

15. Second Messenger Mechanism 4.Adenyl cyclase removes 2 phosphate groups from ATP creating cyclic adenosine monophosphate (cAMP) (second mesenger) 5.cAMP activates or inactivates protein kinases 6.Protein kinases activate specific intracellular enzymes

16. Second Messenger Mechanism 7.Enzymes influence specific cellular reactions (target cell’s response to hormone)

17. Second Messenger Mechanism Summary: Hormone or 1 st messenger binds to plasma membrane receptor Triggers formation of intracellular 2 nd messenger 2 nd messenger activates cascade of chemical reactions Target cell’s response to the hormone is produced

18. Another Second Messenger Some hormones produce effects in target cells by triggering opening of calcium channels –Hormone binds to receptor on plasma membrane –Ca2+ channels open –Ca2+ binds with calmodulin –Ca2+/Calmodulin complex acts as 2 nd messenger –Enzymes are activated/inactivated –Target cell’s response is produced

19. Calcium-Calmodulin as 2 nd Messenger

20. 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

21. Endocrine Feedback Loop

22. 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

23. Regulation of Target Cell Sensitivity Sensitivity of target cell depends on number of receptors it has for a specific hormone Receptors are constantly being broken down and re-synthesized by the cell Up-regulation: synthesis of new receptors > degeneration of old receptors –Increase target cell sensitivity to that particular hormone Down-regulation: synthesis of new receptors < degeneration of old receptors –Decrease target cell sensitivity

24. 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

25. 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)

26. 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

27. 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

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

30. 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

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

32. 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)

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

34. 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

35. 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

36. 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

37. 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

38. Posterior Pituitary Hormones secreted from Posterior Pituitary: –Antidiuretic Hormone (ADH) –Oxytocin (OH)

39. 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

40. ADH Abnormalities Hyposecretion –Diabetes insipidus –Increased urine output of dilute urine –“high and dry” –Na+ levels are increased; Intercellular Fluid- decreased Hypersecretion –Syndrome of inappropriate antidiuretic hormone (SIADH) –Decreased urine output –Fluid overload; low Na+ levels

41. 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

42. 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

43. 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

44. 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

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

46. 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

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

49. Exophthalmos

50. 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

52. 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

54. Calcitonin The 3 rd 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

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