Maintaining the gradient of sodium ions

• What are the two regions of the loop of Henle?

  Descending limb

  Ascending limb
• Where is the gradient of sodium ions kept?

  Loop of Henle
• What is the structure of the descending limb?

  Thin walls

  Permeable to water
• What is the structure of the ascending limb?

  Thick walls

  Impermeable to water
• How does the loop of Henle maintain a sodium ion gradient? the descending limb:

  • Sodium ions are actively transported out of the ascending limb into the interstitial space (space between the limbs)
  • Low water potential in interstitial space
  • Water moves into interstitial space
  • Water potential of filtrate lowers as it moves down the descending limb
• How does the loop of Henle maintain a sodium ion gradient? - the ascending limb

  • At the base of the ascending limb sodium ions diffuse out of the filtrate, so the filtrate gets a higher water potential
  • Gradient established between ascending limb and collecting duct
  • Water moves out of collecting duct into the blood vessels
  • The water potential of the filtrate is lowered
  • Water potential in interstitial space is lowered so water moves down collecting duct
• What ions are actively transported out of the ascending limb?

  Sodium ions
• Where are sodium ions transported to from the ascending limb?

  Interstitial space
• What is the interstitial space?


  Space between the two limbs
• Why does water move into the interstitial space?

  Water potential of the descending limb is greater than that of the interstitial space
• What happens at the base of the ascending limb?

  Sodium ions diffuse out into the collecting duct
• Where does water move to from the collecting duct?

  Blood vessels
• What does the distal convoluted tubule do?

  Selects which ions to absorb