While in the Middle Ages it was believed that the spleen broke down the black bile produced by the liver – an overabundance of black bile was blamed for the outbreak of leprosy, among other things – today we know that spleen tissue acts as a filter for blood and pathogens. The spleen tends to lead a shadowy existence. Very few people know exactly where it is located, let alone what it does. Yet it is the filtering unit of our blood system and an important part of our immune system – and it probably causes side stitches.
What does the spleen look like and where exactly is it located?
The spleen (synonyms: splen, lien) is a relatively small organ – you can’t usually feel it from the outside. It is about 11 cm long, 7 cm wide, and 4 cm thick, and weighs between 150 g and 200 g. It is about the shape of a bean and soft to the touch, varying in color from cherry red to blue-violet.
The spleen is located below the diaphragm in the left upper abdomen: there it borders the stomach, the left kidney and the pancreas. It is connected to the neighboring organs by connective tissue ligaments. From the outside, the spleen is surrounded by a connective tissue capsule (tunica fibrosa), which protects the soft interior.
From it, supporting beams lead inward, between which the splenic pulp (Latin pulpa = flesh) is located. This pulp is divided into the so-called red pulp (pulpa rubra) and white pulp (pulpa alba) – they perform different tasks. The names are related to the appearance of the splenic districts: When the spleen is cut open, the red pulp appears as red tissue in which the white pulp sits as white nodules.
The spleen is supplied with blood via the splenic artery (lienal artery), and blood then flows from the spleen to the liver via the lienal vein. The spleen is particularly well supplied with blood: our entire blood is pumped through it about 500 times every day!
What are the functions of the spleen?
The red pulp consists of a well-perfused connective tissue network (reticulum splenicum), in which old blood cells (erythrocytes) that are no longer so elastic get stuck and are “caught” by the network – they are then broken down by macrophages. In the process, the spleen “recycles” iron from hemoglobin (red blood pigment). Small blood clots and “spent” platelets (blood clots) are also sorted out and broken down in the spleen.
The white pulp is part of our immune system. First, it stores lymphocytes (which are a specific type of white blood cell), some of which also mature in the spleen. About 30 percent of all white blood cells are stored this way. The lymphocytes react to pathogens such as bacteria that enter the spleen with the blood and can thus fight off infection. When needed, the lymphocytes stored in the spleen are also released into the blood. In addition, immunoglobulins are formed in the white pulp, which are special defense substances against pathogens.
In addition, the spleen also always stores a certain amount of blood, which can be released, for example, when there is bleeding in the body or during great exertion. This is probably what causes the side stitch that sometimes plagues us during sports.
The spleen throughout life
In unborn children, the spleen is instrumental in producing blood cells. It usually stops this function after birth – the bone marrow then takes over blood production. However, if bone marrow blood cell production is disrupted by a disease (for example, leukemia), the spleen may become active again.
All the tasks performed by the spleen are also performed by other organs in the body: the bone marrow produces blood cells and the lymph nodes fight invading pathogens. This makes the spleen dispensable; one can survive without it. However, it may possibly increase susceptibility to certain pathogens; for example, pneumococci seem more likely to cause dangerous meningitis or pneumonia – vaccination then provides protection.
