Endocrine System

• Thyroidism


  Problem with the levels of thyroxine in the blood
• Thyroid Stimulating Hormone (TSH)


  • Released by the pituitary gland in the brain
  • Binds to receptors on thyroid gland cells to stimulate them to secrete thyroxine
  • Thyroxine inhibits the pituitary gland so it stops secreting TSH

  
• Thyroxine


  • Hormone released by the thyroid gland
  • Regulates the basal metabolic rate
  • Plays an important role in growth and development by stimulating protein synthesis

  
• Basal metabolic rate


  Metabolic rate at rest
• Iodine is required for the production of thyroxine
• Lack of iodine in the diet


  • Leads to lower levels of thyroxine in the blood (hypothyroidism)
  • Leads to a low basal metabolic rate, lower rates of respiration and less protein synthesis
• Too much thyroxine released

  • Person has hyperthyroidism
  • High basal metabolic rate
  • Higher rates of respiration and higher rates of protein synthesis
• Negative feedback


  • Mechanism that enables homeostasis to occur
  • Maintains a constant internal environment
• Negative feedback, thyroxine and basal metabolic rate

  1. Pituitary gland releases TSH

  2. TSH binds to receptors on thyroid gland cells and stimulates them to secrete thyroxine

  3. Increased thyroxine levels lead to increased basal metabolic rate

  4. Increased thyroxine inhibits pituitary gland from making TSH

  
• Without negative feedback, the pituitary gland would continue to produce TSH and the thyroid gland would continually produce more thyroxine, leading to basal metabolic rate becoming too high

  
• Removal of pituitary gland

  Leads to a decrease in basal metabolic rate
• Adrenaline


  • Hormone made and secreted by the adrenal glands
  • Released in response to scary or stressful situations
  • Leads to the 'flight or fight response'
• Adrenaline release process


  1. Receptors detect stimuli that occur when a dangerous or stressful event occurs

  2. Electrical nerve impulses generated and pass to the brain

  3. Brain perceives danger or stress

  4. Brain generates nerve impulses that travel to the adrenal glands

  5. Adrenal glands release adrenaline into the blood

  6. Adrenaline binds to receptors on target cells to stimulate 'fight or flight' responses
• Responses stimulated by adrenaline to prepare the body for 'fight or flight'


  • Pupil dilation
  • Increased heart rate and strength of contraction
  • Increased breathing rate and volume of air moved
  • Liver cells stimulated to breakdown glycogen into glucose
  • Vasodilation of small arteries leading to capillaries in muscles and brain