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The Endocrine System

The Endocrine System. Chapter 13. Endocrine. to interstitial fluid  circulation exocrine- secreted to ducts  lumen or outside the body Endocrine glands: Pituitary, thyroid, parathyroid, adrenal & pineal Hormone secretion + other functions:

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The Endocrine System

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  1. The Endocrine System Chapter 13

  2. Endocrine • to interstitial fluid circulation • exocrine- secreted to ducts  lumen or outside the body • Endocrine glands: • Pituitary, thyroid, parathyroid, adrenal & pineal • Hormone secretion + other functions: • Hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue & placenta

  3. Figure 13.1

  4. Hormone Operation • General chemical signal in circulation • Slower than nerve responses • Target cells must have a specific receptor • Response determined by responding cell, i.e. different cells may respond differently to the same hormone • Cell may respond to more than one hormone, • i.e. has more than one type receptor

  5. Hormone Chemistry • Soluble in lipids = Hydrophobic • steroids, e.g. testosterone, estrogens, etc. • thyroid hormones, e.g. T3, T4 • Nitric oxide (NO) • Water soluble= Hydrophillic • Amino acid derivatives, e.g. epinephrine, norepinephrine • Peptides, e.g. antidiuretic Hormone (ADH), oxytocin • Proteins, e.g. insulin & growth hormone • General Action depends on chemistry

  6. Lipid Soluble Action • Hormone detaches from carrier in blood stream • Diffusion through interstitial fluid & cell membrane into cell • Binds to & activates receptor • Receptor-hormone complex alters gene expression • If new mRNA protein synthesis • New proteins alter cell activity

  7. Figure 13.2

  8. Water-Soluble Action • Diffuses from blood and binds to receptor in plasma membrane • Starts reaction inside cell forming second messenger • Cyclic AMP is a common one • Second messenger causes activation of several proteins (enzymes) • Activated proteins produce physiological responses • Second messenger is inactivated

  9. Figure 13.3

  10. Control of Secretions • Release occurs in short bursts • Regulated by: • Signals from nervous system, e.g. adrenal medulla release of epinephrine • Chemical changes in blood, e.g Blood Ca2+ affects parathyroid hormone • Other hormones, e.g. ACTH from pituitary stimulates cortisol release from adrenal cortex

  11. Hypothalamus & Pituitary • Major link between nervous & endocrine systems • Hypothalamic Cells synthesize at least 9 hormones • Pituitary synthesizes 7 • Regulate growth, development, metabolism & homeostasis

  12. Pituitary • Two lobes; anterior & posterior • Hypophyseal portal veins • Connect capillaries in hypothalamus to capillaries in anterior pituitary

  13. Hypothalamus  Pituitary • Axons of hypothalamic neurons (neurosecretory cells) end near capillaries of hypothalamus • Secrete Releasing hormones or Inhibiting hormones portal veins • Regulate release of anterior pituitary hormones

  14. Figure 13.4

  15. Human Growth Hormone (hGH) • Promotes synthesis of IGFs = somatomedins • in liver, muscle, cartilage & bone • Released in bursts (~2 hour intervals) • Hypothalamus Growth Hormone Releasing Hormone (GHRH) & Growth Hormone Inhibiting Hormone (GHIH ) • Regulated by blood glucose levels

  16. Thyroid Stimulating Hormone • Stimulates the formation & secretion of Thyroid hormones from thyroid gland • Hypothalamus Thyrotropin Releasing Hormone (TRH)- no TIH • Regulated by circulating thyroid hormone levels

  17. Follicle Stimulating Hormone (FSH) & Luteinizing Hormone (LH) • In females: • FSH starts follicle development • LH stimulates formation of corpus luteum & secretion of progesterone • In males: • FSH stimulates sperm production in testes • LH stimulates release of testosterone • Gonadotrophin releasing Hormone (GnRH) from hypothalamus is suppressed by high levels of estrogen in females and testosterone in males

  18. Prolactin (PRL) • Initiates & maintains milk production by mammary glands • Ejection of milk depends on oxytocin • Prolactin inhibiting hormone (PIH) suppresses prolactin release • High levels of Estrogens  PRH prolactin release • Unknown function in males • Hypersecretion  impotence

  19. Adrenocortcotrophic Hormone (ACTH) • Controls production & secretion of glucocorticoids from adrenal cortex • Corticotrophin Releasing Hormone (CRH) from hypothalamus stimulates secretion of ACTH • Stress related stimuli can also stimulate ACTH release • Glucocorticoids inhibit CRH & ACTH release

  20. Melanocyte Stimulating Hormone (MSH) • Small circulating amounts • Excess causes skin darkening

  21. Posterior Pituitary • axon terminals from hypothalamus- • Release hormones • Oxytocin- enhance smooth muscle contraction during birth & milk ejection • may play role in emotional bonding • Antidiuretic Hormone (ADH) = vasopressin • Causes kidney to retain more water • Vasoconstriction increase in blood pressure • high blood osmotic pressure increase secretion

  22. Figure 13.5

  23. Figure 13.6

  24. Thyroid Gland • Below larynx- two lobes • follicular cells surround follicles •  thyroxin (T4) & triiodothyronine (T3) • Stored in follicle • Parafollicular cells (C-cells) • calcitonin

  25. Figure 13.7a

  26. Figure 13.7b

  27. Thyroid Hormones • T4 & T3 increase basal metabolic rate, protein synthesis & growth • Blood level is controlled via feedback through hypothalamus • Increased body ATP demand can also raise blood levels • Calcitonin inhibits osteoclasts  decrease in blood Ca2+ • Feedback control on blood levels

  28. Figure 13.8

  29. Parathyroid Glands • Small round masses in posterior of thyroid gland • Chief cells release parathyroid hormone (PTH) • Regulator of Ca2+, Mg2+ & HPO42- • Increases number & activity of osteoblasts • Slows loss of Ca2+ & Mg2+ in urine • Promotes production of calcitriol  increases rate of Ca2+, Mg2+ & HPO42- absorption in GI tract

  30. Figure 13.9

  31. Figure 13.10

  32. Pancreas • Fattened organ in curve of duodenum • Mostly an exocrine organ for digestion • Endocrine cells in pancreatic islets • Several cell types: • alpha cells glucagon • beta cells insulin

  33. Figure 13.11a

  34. Figure 13.11b

  35. Figure 13.11c

  36. Actions of Insulin & Glucagon • Low blood glucose stimulates glucagon release • Glucagon stimulates liver glucose release  increased blood glucose • High glucose levels stimulate insulin release • Insulin increase glucose transport into skeletal muscle and adipose cells  decreased blood glucose • Insulin promotes Amino Acid uptake, protein synthesis & lipid storage • ANS also modulates hormone release

  37. Figure 13.12

  38. Adrenal Gland • Near kidneys • Two separate gland structures- • Adrenal cortex and adrenal medulla • 3 zones in Cortex-3 steroid hormones • Outer zone  mineralocorticoids • Middle zone  glucocorticoids • Inner Zone  androgens

  39. Figure 13.13a

  40. Figure 13.13b

  41. Mineralocorticoids • Aldosterone is the major form • Stimulates Na+ reabsorption from urine to blood • Stimulates excretion of K + into urine • Part of renin-angiotensin-aldosterone pathway • Decreased BP  release of renin from kidney • Renin causes angiotensinogen angiotensin I • In lungs Angiotensin converting enzyme (ACE) causes Angiotensin I  angiotensin II • Angiotensin II causes Aldosterone release

  42. Figure 13.14

  43. Glucocorticoid action • Increase rate of protein breakdown • Stimulate liver formation of glucose • Breakdown of triglycerides in adipose • Anti-inflammatory effects- • Inhibit white blood cells • Depresses immune system • Regulated by negative feedback through hypothalamus

  44. Androgens • Small amount secreted from adrenal cortex • Contribute to libido in females • Converted to estrogens by other body tissues • Stimulate axillary hair growth in both boys & girls • Contribute to adolescent growth spurt

  45. Adrenal Medulla • Consists of sympathetic post ganglionic cells • stimulated by preganglionic sympathetic neurons • Releases Epinephrine and norepinephrine • gives systemic sympathetic effects • occurs during strong physiological stress

  46. Gonads • Produce gametes • Release sex steroids (testosterone or estrogen & progesterone) • Also hormone inhibin • Inhibits FSH release • hormones from pituitary (FSH & LH) • Ovaries also produce a hormone relaxin during pregnancy • details later in course

  47. Pineal • Small gland attached to roof of third ventricle of brain • Produces melatonin • Sets bodies biological clock • More released in darkness

  48. Other hormones • Prostaglandins (PG) & leukotrienes (LT) • Derived from fatty acids • Act locally in most tissues & released from most body cells • LTs stimulate white blood cells & mediate inflammation • PGs affect many visceral functions & also modulate inflammation, promote fever & intensify pain

  49. Stress Responses • Part of homeostatic responses • When successful leads to extra physiological capacity and long term adaptation • Initial “fight-or-flight” response • Nerve mediated response-sympathetic

  50. Stress- Resistance Reaction Slower & longer Than initial response • Hypothalamus  Increased CRH, GHRH, TRH • CRHACTHCortisol  mobilize metabolites (amino acids, glucose & fat) • GHRHhGH mobilize fats & glucose for energy and promote tissue growth & repair • TRHTSHthyroid hormones increased Metabolic capacity

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