The urinary system maintains an appropriate fluid volume by regulating the amount of water that is excreted in the urine.

泌尿系统通过调节尿中排泄的水量来维持适当的液体量。

This 3 liters of fluid needs to find a way back into the blood so that the body's interstitial fluid volume and blood volume both stay constant over time.

这3升液体需要寻找回到血液的途径，以便于间质液量和血液量都总是维持恒定。

Concentration gradients cause water to follow sodium, so we end up with the excess water being excreted in the urine with the sodium, normalizing the fluid volume in the blood.

（尿钠）浓度改变会导致水随着钠的排出而流出，最终多余的水从尿液中排出，血容量恢复正常。