Counter current multiplier effect

Purpose and effect of counter current multiplier effect:

build up the salt concetrations in the surrounding medulla still further.

The important factor is that the ascending limb and descending limbs are next to each other with the filtrate flowing in opposite directions. This is why it is called counter-current

water dedcending

salt ascending

The result of water leaving the descending limb and salt being pumped out of the ascending limb is that the salt concentration of the filtrate is lower than the salt concentration of the filtrate that first entered the nephron.

2. salt→ medulla - salt

   water-descending limb - salt

   con reaching LH is —- from before

Because salt been pumped out into the medulla before, the medulla now has a higher salt concentration than it did.

more water leaving the descending limb than would have occurred with lower salt concentrations in the surrounding medulla.

This means that the concentration of salt that reaches the bottom of the loop of Henle is now higher than it was before.

In the last it was 400, now it has gone up to 500 - as an example. Because of this there is more salt available in the filtrate to be pumped out of the ascending limb into the medulla. The result is that the salt concentration of the surrounding medulla is now even higher that it was before

3

Because the medulla has an even higher salt concentration,

more water leaves the descending convoluted tubule by osmosis.

Water would move by osmosis until the concentations on the two sides are equal if the filtrate was not moving through the nephron.

Because it is moving it does not get the chance to reach an equilibrium.

Because even more water has left the descending limb, the salt concentrations at the bottom of the loop of Henle are now very high. This is despite the fact that the salt concentrations of the filtrate entering the nephron is always the same. Due to these very large concentrations of salt in the filtrate at the bottom of the loop of Henle, there is now even more salt available for the ascending limb to pump out into the medulla.