Which system controls water balance in the body?

The excretory system plays a crucial role in maintaining water balance in the body through various mechanisms. It is primarily responsible for filtering blood, removing waste, and regulating the composition of bodily fluids. The kidneys, a key component of the excretory system, adjust the volume and concentration of urine produced in response to the body's hydration status.

When the body is dehydrated, the kidneys conserve water by reabsorbing it into the bloodstream, leading to more concentrated urine. Conversely, when there is an excess of water, the kidneys can excrete more dilute urine. This regulation is critical for maintaining homeostasis, ensuring that the total body water content remains within a narrow range, which is vital for cellular function and overall bodily health.

While the nervous system and endocrine system also contribute to water regulation—through signaling mechanisms like hormones (such as antidiuretic hormone) and nerve responses—it's the excretory system that directly manages water balance through urine production and excretion. The digestive system, on the other hand, is more involved in nutrient absorption and does not have a primary role in water balance.