Which organ is primarily responsible for filtering blood and producing urine?

The kidney is primarily responsible for filtering blood and producing urine. It plays a crucial role in the body's homeostasis by regulating the volume and composition of blood. This involves the removal of waste products, excess substances, and toxins from the bloodstream. The functional units of the kidney, called nephrons, filter blood, reabsorb essential substances, and excrete waste in the form of urine. This process is vital for maintaining the body’s fluid balance and electrolyte levels.

In contrast, the liver plays a significant role in metabolism, detoxification, and the production of bile. The spleen is involved in filtering blood, but its primary functions relate to the immune system and recycling iron from red blood cells, rather than urine production. The pancreas serves both endocrine and exocrine functions, notably in digestion and blood sugar regulation, but it does not filter blood or produce urine.