What is the primary function of the spleen?

The primary function of the spleen is filtering old red blood cells. The spleen plays a crucial role in the body's immune response and blood maintenance. It identifies and removes aged, damaged, or dysfunctional red blood cells from circulation, which helps maintain healthy blood composition. This process is essential for recycling iron from the hemoglobin in red blood cells for reuse in new cells and for helping to prevent the accumulation of damaged cells in the bloodstream.

Additionally, the spleen is involved in the production of antibodies and the storage of white blood cells, contributing to the immune system's ability to respond to infections. Thus, filtering old red blood cells is one of the key functions of this organ, making it vital for overall health and homeostasis.