What are the main functions of the kidneys?

The kidneys play a vital role in maintaining homeostasis in the body primarily through their ability to filter blood and regulate electrolytes. They filter out waste products and excess substances from the bloodstream, creating urine as a way to excrete these materials from the body. This function is essential for the removal of toxins and metabolic waste, ensuring that the internal environment remains stable and balanced.

In addition to filtration, the kidneys regulate the concentration of various electrolytes, such as sodium, potassium, and calcium, which are crucial for many physiological processes, including nerve conduction, muscle function, and maintaining overall fluid balance. By adjusting the excretion or reabsorption of these electrolytes as needed, the kidneys help to keep bodily functions running smoothly.

The other options reflect functions that either do not take place in the kidneys or are unrelated to their primary roles. For instance, while hormones are produced by the kidneys—such as erythropoietin and renin—the main function highlighted in the question is filtration and regulation. The production of nerve impulses and the absorption of nutrients and oxygen pertain to entirely different systems and organs, such as the nervous system and the gastrointestinal system, respectively. Thus, filtering blood and regulating electrolytes is the most accurate description of the primary functions