The Nephron Loop

The loop of Henley is what really does the reabsorbing or concentrating. And so as animals move into areas more likely to be dehydrated, say like deserts, or even going back into the saltwater, they need to make a longer loop. So that's why we filter 180 liters a day. But we don't pee out 180 liters right like a fresh fish. We reabsorb it like a saltwater fish. Some animals can just do two times and some can go 25 times more concentrated in their blood.