Homeostasis

• Homeostasis


  • the maintenance of a constant internal environment
  • allows an organism to be independent from changes in the external environment
  • e.g. regulating body temperature, regulating the water potential of blood and tissue fluid, regulating blood glucose concentration
  • negative feedback : the body reacts to bring about an opposite effect to the changes detected
• Negative Feedback

  • the body reacts to bring about an opposite effect to the changes detected

  1. normal level or set point
  2. stimulus in which there is a change in the internal environment
  3. a receptor detects the stimulus and sends signals to the control centre
  4. the corrective mechanism brings about a reverse effect to the stimulus
  5. condition decreases back to set point
• Regulating Blood Water Potential - Increase

  1. normal blood potential in blood
  2. water potential of blood increases (e.g. due to large intake of water)
  3. hypothalamus is stimulated
  4. less ADH released by the pituitary gland into the bloodstream, less ADH transported to the kidneys. Cells in the walls of the collecting ducts become less permeable to water. Less water is reabsorbed into the bloodstream. More water excreted and more urine is produced. Urine is more diluted
  5. water potential of blood decreases back to normal level
• Regulating Blood Water Potential - Decrease


  1. normal blood potential in blood
  2. water potential of blood decreases (e.g. due to profuse sweating)
  3. hypothalamus is stimulated
  4. more ADH released by the pituitary gland into the bloodstream, more ADH transported to the kidneys. Cells in the walls of the collecting ducts become more permeable to water. more water is reabsorbed into the bloodstream. less water excreted and less urine is produced. Urine is more concentrated
  5. water potential of blood decreases back to normal level