Loop of Henle

• What does the loop of Henle do?


  Maintains a sodium ion gradient
• Where is the loop of Henle located?


  in the medulla of the kidneys
• What is the loop of Henle made up of ?


  Two 'limbs' - the descending limb and the ascending limb
• what do the limbs of the loop of Henle control?


  the movement of sodium ions so that the water can be reabsorbed by the blood
• (1) What happens near the top of the ascending limb?

  Na+ ions pumped out into MEDULLA by active transport

  Ascending limb impermeable to water, so the water stays inside the tubule

  = creates a low ψ in medulla, because there is a high conc of ions
• (2) what happens next

  Because there's a lower ψ in the medulla than in descending limb, water moves out the descending limb (permeable to water) by OSMOSIS

  = This makes the filtrate more concentrated - ions cannot diffuse out because the descending limb is not permeable to them.

  • The water in the medulla is reabsorbed into the blood through the capillary network
• (3) what happens next

  Near the bottom of the ascending limb Na+ ions diffuse out in the medulla, further lowering the ψ in the medulla.

  Ascending limb is impermeable to water , so it stays in the tubule
• (4) what happens next

  Water moves out the DCT by osmosis and is reabsorbed into the blood
• DCT= 


  distal convoluted tubule
• (5) what happens next??

  The first 3 stages massively increase the ion conc in the medulla, which lowers the ψ.

  • this causes water to move out the collecting duct by osmosis
  • the water in the medulla is reabsorbed into the blood through the capillary nextwork
• Summarise the 5 steps, briefly

  1. (top)Ascending limb- Na+ ions pumped out. Water stays inside
  2. water moves out the descending limb. ions stay inside
  3. (bottom)ascending limb Na+ diffuse out. water stays inside
  4. water moves out DCT - reabsorbed into blood
  5. lowers ψ = water moves out collecting duct. water in medulla reabsorbed into blood
• What controls the volume of water reabsorbed into the capillaries?

  The volume of water reabsorbed into the capillaries is controlled by changing the PERMEABILITY of the DCT and the COLLECTING DUCT