Endocrine system

• Hypothalamus


  The boss
• Main function of the hypothalamus


  • Maintaining the body's balance
  • Managing blood pressure and gut distension
  • Controlling circadian rhythms
  • Receiving signals from thermoreceptors and osmoreceptors to regulate bodily functions
  • Detecting harmful substances in the bloodstream and causing vomiting
  • Regulating behaviours such as eating and reproduction
• Thermoregulation - Cold


  1. Skin temp down

  2. Heat sensors send impulse to hypothalamus

  3. Hypothalamus sends impulses to effectors: hair follicles, muscles, blood vessels
• Thermoregulation - Hot


  Receptors in hypothalamus stimulate: blood vessels to dilate, sweat glands to increase output
• Antidiuretic hormone (ADH)


  Regulates water balance by controlling water reabsorption in kidneys
• Kidney & Water Regulation - High osmolarity

  1. Osmoreceptors detect high osmolarity

  2. Pituitary gland releases more ADH

  3. ADH increases water permeability in kidney tubules

  4. More water reabsorbed, less excreted

  5. ECF osmolarity decreases
• Kidney & Water Regulation - Low osmolarity

  1. Low osmolarity detected

  2. ADH release reduced

  3. Water permeability in kidney tubules decreases

  4. More water excreted

  5. ECF osmolarity increases
• Posterior lobe of pituitary gland

  • Controlled by nerve fibers from hypothalamic neurons
  • Releases ADH and oxytocin
• Anterior lobe of pituitary gland


  • Influenced by substances transported from hypothalamus via blood vessels
  • Releases growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, gonadotropic hormones
• Hypothalamus


  Controls almost all secretions of the pituitary gland
• Posterior lobe of pituitary

  Controlled by nerve fibers from hypothalamus
• Anterior lobe of pituitary


  Controlled by hormones released from hypothalamus
• Releasing hormones


  Hormones released by hypothalamus that signal anterior pituitary to produce and release certain hormones
• Inhibiting hormones


  Hormones released by hypothalamus that signal anterior pituitary to stop or reduce production and release of certain hormones
• Thyroxin (T4)


  Thyroid hormone involved in regulating metabolism and other body functions
• Calcitonin


  Hormone produced by thyroid gland that regulates calcium levels and promotes calcium deposition in bones
• Conversion of T4 to T3

  T4 is converted to the active form T3 in target cells
• Triiodothyronine (T3)


  The active form of thyroid hormone that exerts effects on target tissues
• Effects of T3


  • Increases metabolic rate
  • Increases rate and strength of heartbeat
• Glucagon


  Hormone secreted by alpha cells in pancreas that promotes breakdown of glucose, fatty acids, and amino acids
• Insulin


  Hormone secreted by beta cells in pancreas that promotes storage of glucose, fatty acids, and amino acids
• Insulin production triggered by high blood glucose

  1. Beta cells have receptors that detect high glucose

  2. This triggers insulin production and release to lower blood glucose
• Somatostatin


  Hormone produced by delta cells in pancreas that inhibits release of other hormones like insulin and glucagon
• Islets of Langerhans


  • Innervated by parasympathetic and sympathetic neurons
  • Nervous signals modulate secretion of insulin and glucagon
• Parasympathetic stimulation


  Enhances insulin secretion, inhibits glucagon secretion
• Sympathetic stimulation


  Inhibits insulin secretion, stimulates glucagon secretion
• Insulin and glucagon are important in regulation of carbohydrate, protein and lipid metabolism
• Glucose Tolerance Factor (GTF)


  Substance produced by liver that is essential for insulin to function properly
• Liver as target organ for insulin

  Liver stores excess glucose as glycogen in response to insulin signals
• Liver's role in cholesterol


  • Produces cholesterol
  • Packages cholesterol for transport
  • Cholesterol is precursor for steroid hormones
  • Breaks down hormones for disposal or recycling
• Cortical hormones


  Steroid hormones produced by adrenal cortex
• Aldosterone


  Mineralocorticoid hormone that regulates electrolyte balance and blood pressure
• Gonadocorticoids


  Sex hormones (androgens and oestrogens) produced by adrenal cortex
• Adrenaline and noradrenaline


  Hormones secreted by adrenal medulla in response to sympathetic nerve stimulation, prepare body for "fight or flight"
• Prolonged stress


  Leads to prolonged secretion of adrenaline and noradrenaline, causing circulatory stress