Which organ in the body acts as a filter for blood and recycles old red blood cells?

The spleen is the organ that functions as a filter for blood and is responsible for recycling old red blood cells. It plays a crucial role in the body's immune system by filtering out pathogens and debris from the bloodstream. As red blood cells age, they become less functional and are processed by the spleen, which helps to break them down and recycle their components, such as iron, for use in new red blood cell production.

The liver, while also involved in detoxification and metabolism, does not primarily filter blood in the same way that the spleen does, nor does it specialize in recycling red blood cells. The kidneys are primarily responsible for filtering waste products from the blood to form urine, but they do not recycle red blood cells. The pancreas has a role in digestion and regulating blood sugar but does not filter blood or handle red blood cell recycling. Thus, the spleen is specifically adapted for the tasks of filtering blood and recycling old red blood cells, making it the correct answer.