The spleen is an organ located in the left upper quadrant of the abdomen and is roughly the size of a clenched fist. In the adult, the spleen functions mainly as a blood filter, removing old red blood cells. It also plays a role in both cell-mediated and humoral immune responses. The spleen is a soft, vascularised organ with a fibro-elastic capsule, which allows it to carry out many functions.
The spleen contains two types of tissues with different functions- white pulp and red pulp.
The white pulp plays an important role in the normal immune response to infection. Antigen presenting cells can enter the white pulp, and then trigger a cascade of reactions, resulting in the production of IgM and IgG antibodies. Additionally, the white pulp is important for dealing with encapsulated bacteria, and the B-lymphocytes in the white pulp help to opsonise the bacteria.
The red pulp makes up the majority of the spleen parenchyma (functional tissue of an organ). Its main functions are to remove old, damaged and dead red blood cells, sequester platelets, carry out phagocytosis of opsonised bacteria by macrophages. Prenatally it is haematopoietic until about the fifth month of gestation when bone marrow becomes the main site for haematopoiesis.
In this section, learn more about the physiology of the spleen- read about the functions of the spleen.