OCR F214 EXCRETION - Water Reabsorption

Hi,
Can anyone explain the water reabsorption system in the loop of hence to me? I don't understand the hairpin counter multiplier. What would you write to explain it, for example if it came up in an 8 mark question?

Reply 1

beth16x

Original post by brainmatter

I'm not sure if this is sufficient enough but here's some stuff on it...

The countercurrent multiplier is derived from the ascending limb and descending limb which run in opposite directions and seperated by the interstital space of the renal medulla.
Near the top of the ascending limb of the loop of Henle, Na+ and Cl- ions are actively pumped out into the medulla but it is impermeable to water (due to a lack of aquaporin) so the water stays inside the tubule. This creates a low water potential in the medulla because theres a high concentration of ions. This low water potential means water moves out of the descending limb into the medulla by osmosis making the filtrate more concentrated. The water in the medulla is reabsorbed into the blood through the capillary network. Near the bottom of the ascending limb, Na+ and Cl- ions diffuse out into the medulla, further lowering the water potential and increasing the ion concentration in the medulla. So, water moves out of the collecting duct by osmosis, and the water in the medulla is reabsorbed into the blood through the capillary network.

The longer an animal's loop of Henle, the more water they can reabsorb from the filtrate.