Which organ is responsible for filtering waste like urea and proteins from the blood?

The kidney is the primary organ responsible for filtering waste products from the blood, including urea, creatinine, and excess nutrients. It performs this essential function through a complex process that involves filtration, reabsorption, and secretion within its functional units called nephrons. The kidneys regulate not only waste removal but also maintain the body's electrolyte balance, acid-base homeostasis, and blood pressure by controlling the volume of fluid and the composition of the blood.

In the context of waste management, urea, which is a byproduct of protein metabolism, is produced in the liver and then transported to the kidneys for excretion. The kidneys ensure that these waste products are effectively removed from circulation, thus preventing toxicity.

The liver, though involved in filtering blood and processing various substances, primarily focuses on metabolism and detoxification rather than direct filtration of blood for waste excretion. The pancreas is mainly involved in digestion and the regulation of blood sugar levels. The spleen plays a role in filtering blood as well but primarily focuses on the recycling of red blood cells, the storage of platelets, and the immune response. Therefore, the kidneys stand out as the key organ for filtering waste like urea and proteins from the blood.