Final answer:
The kidneys primarily function to filter blood, which includes the removal of waste products, regulation of blood pressure, and maintenance of homeostasis, including proper ion and water balance.
Step-by-step explanation:
The function of the kidney is filtration of blood. This vital organ maintains the homeostatic balance of bodily fluids by filtering waste products, like urea, from the blood and excreting them with water as urine. Kidneys also regulate important bodily functions such as blood pressure, glucose metabolism, and erythropoiesis (production of red blood cells). The nephron, which is the functional unit of the kidney, actively filters blood and generates urine.
In addition, kidneys help maintain the proper balance of water and salts, control blood pH, and regulate red blood cell levels and blood pressure. When the blood pressure increases, the blood vessels supplying the kidney can contract or relax to maintain a steady rate of filtration.