Spleen

Spleen resembles a purple fist tucked under the left ribs, rich in blood vessels and soft pulp. Blood enters through the splenic artery and slows within the red pulp, where macrophages inspect red blood cells for damage. Old or misshapen cells are dismantled, with iron shipped back to the bone marrow for reuse and bilirubin sent to the liver.

The white pulp forms islands of lymphoid tissue packed with B cells, T cells, and dendritic cells. As blood passes through, these immune sentinels detect microbes and mount responses, releasing antibodies and signaling other organs to join the defense. The spleen also acts as a reservoir, storing platelets that can be released rapidly during injury to help stop bleeding.

During fetal development the spleen contributes to blood cell formation. In adults the bone marrow handles most production, but the spleen can resume this role if marrow is stressed. Its strategic position makes it vulnerable to trauma from blows to the abdomen; splenic ruptures can cause internal bleeding and require emergency care.

Some people live without a spleen due to injury or disease. Other organs, such as the liver and lymph nodes, take over many duties, but the risk of serious infections rises. Physicians recommend vaccines against encapsulated bacteria like pneumococcus and meningococcus for anyone lacking a spleen and encourage prompt treatment for fevers.

Maintaining spleen health involves wearing seat belts, using protective gear during contact sports, and treating infections quickly. Researchers study how splenic immune cells coordinate responses to parasites, cancers, and autoimmune diseases, seeking therapies that harness this hidden but vital organ.