Osmoregulation

• What is the control of water potential in body fluids called?

  Osmoregulation
• Why is osmoregulation important?

  It is a key part of homeostasis
• What specialized sensory neurons monitor blood water potential?

  Osmoreceptors
• Where are osmoreceptors located?

  In the hypothalamus of the brain
• What happens when osmoreceptors detect a decrease in blood water potential?

  Nerve impulses are sent to the posterior pituitary gland

  
• What hormone is released by the posterior pituitary gland in response to low water potential?

  Antidiuretic hormone (ADH)

  
• What effect does ADH have on the kidneys?

  It causes them to reabsorb more water

  
• How does ADH travel in the body?

  It enters the blood and travels throughout
• How is water reabsorbed in the nephron?

  By osmosis from the filtrate
• Where does water reabsorption occur in the nephron?

  In the collecting ducts

  
• What does ADH do to the luminal membranes of collecting duct cells?

  Increases their permeability to water
• How does ADH increase water permeability in collecting duct cells?

  By increasing the number of aquaporins
• What are aquaporins?

  Water-permeable channels in cell membranes
• What happens to aquaporins in collecting duct cells when ADH binds to receptors?

  They are activated and fuse with membranes
• What occurs as the filtrate travels along the collecting duct?

  Water moves into tissue fluid and blood plasma
• What happens to the filtrate as it loses water in the collecting duct?

  It becomes more concentrated
• What is produced as a result of water reabsorption in the kidneys?

  A small volume of concentrated urine

  
• What happens if the water potential of the blood is too high?

  No ADH is released
• What occurs when osmoreceptors are not stimulated?

  No nerve impulses are sent to the posterior pituitary gland

  
• What happens to aquaporins when no ADH is released?

  They are moved out of the luminal membranes
• What is the result of collecting duct cells being impermeable to water?

  A large volume of dilute urine is produced
• What is the process of osmoregulation in response to low blood water potential?

  • Osmoreceptors detect low water potential
  • Nerve impulses sent to posterior pituitary gland
  • ADH released into the blood
  • ADH increases water reabsorption in kidneys
  • Produces small volume of concentrated urine

  
• What is the process of osmoregulation in response to high blood water potential?

  • Osmoreceptors are not stimulated
  • No nerve impulses sent to posterior pituitary gland
  • No ADH released
  • Aquaporins removed from membranes
  • Produces large volume of dilute urine