How many systems does the spleen help? How many roles does the spleen have?

The spleen is a small organ located in the abdomen, just behind the stomach. It is sort of a "multipurpose" organ, and has roles in the circulatory, lymphatic, and immune systems. 

Though the spleen is quite small, it plays a big part in making sure we have healthy blood circulating through our bodies. The spleen's most important role is to filter out any red blood cells which are beginning to break down. The spleen can recycle usable components from these cells, like iron, in making new red blood cells. The spleen also serves to store blood in its highly elastic vascular tissue, so that if one sustains an injury or loses blood, these reserves can be put to use.

As a part of the lymphatic system, the spleen can detect and filter out bacteria and viruses. In the event of (potential) infection, the spleen helps to produce lymphocytes, which are cells that attack and break down illness-causing agents. Lymphocytes are also produced in the lymph nodes. In this function, the lymphatic and immune systems are highly connected, as it is the production of lymphocytes that helps to protect the body from infection.