Prove that the body is a complete system.

Each organ system performs specific functions for the body, and each organ system is usually studied independently. However, organ systems also work together to help the body maintain homeostasis.
For example, the cardiovascular, urinary and lymphatic systems help the body control water balance. The cardiovascular and lymphatic systems transport fluids throughout the body and help sense both the solute and water levels and regulate pressure. If the water level gets too high, the urinary system produces more dilute urine (urine with a higher water content) to help eliminate excess water. If the water level gets too low, more concentrated urine is produced so that water is retained.