B12 - Homeostasis in action

• Control of body temperate negative feedback loop


  • Body temperature too high
  • detected by thermoregulatory centre
  • blood vessels dilate (vasodilation)
  • swet produced from the sweat glands
  • energy transferred from skin to environment
  • body temperature falls
  • Body temperature too low
  • blood vessels constrit (vasoconstriction)
  • sweating stops and skeletal muscles contract, causing shivering
  • body temperature rises
• Thermoregularatory centre

  • Monitors and controls body temperature
  • In the brain
  • Contains receptors sensitive to blood temperature
• The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre
• Waste products


  • The digestion of proteins from food results in excess amino acids
  • These amino acids are deaminated in the liver to form ammonia
  • Ammonia is toxic, so it is immediately converted to urea for safe extraction
• • Water leaves the body through the lungs during exhalation
  • Water, ions, and urea are lost from the skin in sweat
  • The body has no control over these losses
• Excess water, ions and urea are removed by the kidneys in urine
• The kidneys


  • The kidneys produce urine by filtration of the blood and selective reabsorbtion of useful substances such as water, glucose, and some ions
• Water level in the blood is controlled by the hormone ADH, which afffects the amount of water absorbed by the kidney tubules
• Water levels negaive feedback loop

  • Water conentration too high
  • less ADH released from the pituatary glamd
  • kidney tubules absorb less water
  • levels return to normal
  • Water concentration too low
  • more ADH released from the pituatary gland
  • kidney tubules absorb more water
  • levels return to normal
• Kidney dialysis


  • blood temporarily removed from patient's body
  • filtered through a dialysis machine
  • patient's blood passes over dialysis fluid
  • dialysis fluid has no urea
  • urea and waste products diffuse from high concentration in patient's blood to low concentration in dialysis fluid
  • patient's blood returned to their body