Spleen

The spleen is an immune system organ.

Function of the spleen

The spleen is a secondary lymphoid organ. In other words, it contributes to the immune response but is not involved in the synthesis or maturation of immune cells.

The spleen also plays a role in the maturation of red blood cells and in purifying blood by removing waste (degraded or unusable red cells, damaged platelets, viruses, and cell waste).

The spleen is also involved in the production of blood cells (hematopoiesis) in the foetus. In turn the liver and bone marrow then take on this role.

Structure of the spleen

The spleen is a soft organ measuring 12 cm x 8 cm x 4 cm on average, and weighing approximately 200 grams. This makes it the largest lymphoid organ in the human body. It is located in the abdominal cavity to the left of the stomach.

The spleen is covered by a very fragile connective tissue capsule. Inside, it is composed of two quite distinct parts.

• the surface red pulp filters red cells and is used as a monocyte reservoir;
• the white pulp is composed of lymphoid follicles which activate the immune response via cellular and humoral (antibody) pathways.