Which system is primarily responsible for bodily fluid balance?

The urinary system is primarily responsible for maintaining bodily fluid balance because it regulates the volume and composition of body fluids by filtering blood, removing waste products, and producing urine. This system plays a crucial role in homeostasis by controlling the amount of water and electrolytes in the body. Through processes like filtration in the kidneys and reabsorption in the renal tubules, the urinary system ensures that the body's fluids remain within optimal ranges, thus preventing dehydration or fluid overload.

While the endocrine system does play a role in fluid balance through hormones such as antidiuretic hormone (ADH) and aldosterone, its function is mainly to signal and regulate various processes rather than directly managing fluid levels. The nervous system is involved in coordinating the body’s responses and can influence fluid balance through its control of the kidneys, but it does not directly manage fluid processes. The muscular system is not directly involved in fluid balance; its primary role is movement and stability of the skeleton. Therefore, the urinary system stands out as the primary system tasked with the direct management of bodily fluids.