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I'm not understanding the ascending loop of henle.
So the solute concentration in the medulla increases as you descend deeper into it. Therefore, it makes sense that water inside the loop of henle will passively diffuse out of the descending loop since the descending loop is highly permeable to water.
Then, once you hit the turn (transition between descending and ascending loop) the fluid in the loop of henle is isotonic to the medulla.
As you ascend the thin-walled ascending loop, sodium and calcium ions passively move out since the previously isotonic loop-of-henle-fluid is now hypertonic as you ascend in the medulla.
Here's where I am lost.
1. Why is the thick-walled ascending loop impermeable to ions? Is this one of those "it just is" types of things?
2. The reason why ions diffuse into the medulla in the thin-walled ascending loop is because of the concentration gradient. In the thick-walled ascending loop, the concentration gradient doesn't really matter because the loop is impermeable to ions. So why pump out the ions?
So the solute concentration in the medulla increases as you descend deeper into it. Therefore, it makes sense that water inside the loop of henle will passively diffuse out of the descending loop since the descending loop is highly permeable to water.
Then, once you hit the turn (transition between descending and ascending loop) the fluid in the loop of henle is isotonic to the medulla.
As you ascend the thin-walled ascending loop, sodium and calcium ions passively move out since the previously isotonic loop-of-henle-fluid is now hypertonic as you ascend in the medulla.
Here's where I am lost.
1. Why is the thick-walled ascending loop impermeable to ions? Is this one of those "it just is" types of things?
2. The reason why ions diffuse into the medulla in the thin-walled ascending loop is because of the concentration gradient. In the thick-walled ascending loop, the concentration gradient doesn't really matter because the loop is impermeable to ions. So why pump out the ions?