What is the function of the kidneys in the urinary system?

The kidneys play a crucial role in the urinary system primarily by filtering waste products from the blood and producing urine. They are responsible for maintaining homeostasis by regulating the composition and volume of bodily fluids. As blood passes through the kidneys, they remove excess substances and toxins, including urea, creatinine, and various ions. This filtration process occurs in structures called nephrons, where blood is filtered, and essential substances are reabsorbed back into the circulation while waste products are excreted as urine.

In addition to waste filtration, the kidneys help to regulate electrolyte balance, blood pressure, and blood pH, contributing significantly to the body's overall metabolic and fluid balance. Thus, their primary function in the urinary system is accurately captured by the response indicating their role in filtering waste and producing urine.