What is primarily eliminated through the function of the kidneys?

The primary function of the kidneys is to filter blood and remove waste products from the body, which categorizes metabolic waste products as the primary element they eliminate. These waste products include urea, creatinine, uric acid, and various other byproducts of metabolic processes. The kidneys play a crucial role in maintaining homeostasis by regulating the composition of bodily fluids, ensuring that harmful substances are excreted while retaining essential ones.

In addition to metabolic waste, the kidneys do regulate the balance of electrolytes and water, but these are part of their regulatory functions that maintain overall fluid and electrolyte balance rather than being the main focus of elimination. Oxygen is not eliminated through the kidneys; it is primarily exchanged in the lungs. Thus, the option highlighting metabolic waste products distinctly captures the primary role of the kidneys in excretion.