What organ is responsible for filtering blood and producing urine?

The kidneys are the organs responsible for filtering blood and producing urine. Their primary role in the urinary system involves the removal of waste products and excess substances from the bloodstream. This filtering process helps maintain the body's fluid and electrolyte balance, as well as regulate blood pressure and other critical bodily functions.

The kidneys achieve this by using nephrons, the functional units of the kidneys, which filter blood through a series of intricate processes, including filtration, reabsorption, and secretion. As blood passes through the nephrons, waste materials such as urea, creatinine, and toxins are removed, while essential nutrients and water are reabsorbed back into the bloodstream. The end product of this complex process is urine, which is then stored in the bladder until it is excreted from the body.

In contrast, the liver primarily functions in metabolism and detoxification, and while it plays a role in waste elimination, it does not produce urine. The bladder is the storage organ for urine created by the kidneys and does not filter blood or produce urine itself. The spleen is involved in filtering blood as part of the immune system, but it does not produce urine either. Thus, the main responsibility for urine production and blood filtration lies with the kidneys.