What body system is responsible for maintaining fluid balance and filtering blood?

The renal system, also known as the urinary system, plays a crucial role in maintaining fluid balance and filtering blood. It consists of the kidneys, ureters, bladder, and urethra. The primary function of the kidneys is to filter waste products and excess substances from the blood, which are then excreted as urine. This process is vital for regulating the body's electrolyte levels, blood volume, and overall fluid balance. The kidneys also help in controlling blood pressure and maintaining the pH level of the blood.

While the circulatory system is important in transporting blood throughout the body and facilitating the distribution of nutrients and oxygen, it does not directly filter blood or maintain fluid balance. The nervous system is primarily responsible for transmitting signals and coordinating body functions, rather than directly engaging in fluid regulation. The endocrine system, although involved in regulating various functions through hormones, does not filter blood or manage fluid levels in the same way the renal system does. Thus, the renal system is indeed the correct answer for its specific role in these vital processes.