What is the primary function of the kidneys?

The primary function of the kidneys is to filter and excrete waste. The kidneys are vital organs in the renal system, responsible for removing waste products and excess substances from the bloodstream, which are then excreted as urine. This process helps to maintain the body’s fluid balance, regulate electrolytes, and ensure that blood pressure remains stable. Additionally, the kidneys play a critical role in regulating pH levels in the body and contribute to the overall homeostasis by removing metabolic waste, such as urea and creatinine, that could be harmful if allowed to accumulate.

While other options refer to important processes in the body, they do not accurately describe the main role of the kidneys. For instance, circulating blood is primarily the function of the heart, while insulin production is the responsibility of the pancreas. Nutrient absorption mainly occurs in the intestines, not the kidneys. Hence, the function of filtering and excreting waste distinctly highlights the kidneys' role in maintaining the body's internal environment.