What is the primary function of the urinary system?

The primary function of the urinary system is to remove waste products and regulate water balance. This system plays a crucial role in maintaining homeostasis by filtering the blood to eliminate unwanted substances such as urea, creatinine, and other metabolites produced by the body's cellular processes. By controlling the excretion of water and electrolytes, the urinary system also helps regulate blood pressure and maintain the balance of body fluids. Additionally, it contributes to the acid-base balance of the body by excreting hydrogen ions and reabsorbing bicarbonate as needed.

In contrast, regulating hormones is primarily the domain of the endocrine system, while digestion and absorption are functions of the gastrointestinal system. Transporting nutrients in the blood is a function of the circulatory system, which is responsible for delivering nutrients to cells throughout the body. Thus, the urinary system's specific focus is on waste removal and fluid balance, which is encapsulated by the correct answer.