This is how the spleen works as a filter for our blood

While in the Middle Ages, it was believed that the spleen breaks down the black bile produced by the liver – an excess of black bile was blamed for the outbreak of leprosy, among other things – we now know that the spleen tissue acts as a filter for blood and pathogens. The spleen tends to lead to a shadowy existence. Very few people know exactly where it is, let alone what it does. It is the filter system of our blood system and an essential 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 usually cannot 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. Roughly shaped like a bean, it is soft to the touch and varies in colour from cherry-red to purplish-blue.

The spleen is located below the diaphragm in the left upper abdomen:  It borders the stomach, the left kidney and the pancreas, i.e. the pancreas. It is connected to the neighbouring organs by ligaments of connective tissue. From the outside, the spleen is surrounded by a connective tissue capsule (tunica fibrosa) that protects the soft interior.

Supporting beams lead inwards from it, where the spleen pulp (lat. pulp = flesh) sits. This pulp is divided into the so-called red pulp (Pulpa rubra) and white pulp (Pulpa alba) – they fulfil different tasks. The names are related to the appearance of the spleen areas: If you cut open the spleen, 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 (lien artery); from the spleen, the blood flows via the spleen vein to the liver. The spleen is particularly well supplied with blood: all of our blood is pumped through it about 500 times a day!

 

What are the functions of the spleen?

The red pulp consists of a well-supplied connective tissue network (reticulum splenium) in which old blood cells (erythrocytes) get caught, which are no longer so elastic and are “caught” by the network – macrophages then break them down. The spleen “recycles” the iron from the haemoglobin (red blood pigment). Small blood clots and “used” thrombocytes (blood platelets) are sorted and broken down in the spleen.

The white pulp is part of our immune system. On the one hand, it stores lymphocytes (a type of white blood cell), some of which also mature in the spleen. About 30 per cent 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 an infection. When needed, the lymphocytes stored in the spleen are also released into the blood. In addition, immunoglobulins are formed in the white pulp; these are special defences against pathogens.

In addition, the spleen permanently stores a certain amount of blood, which can be released, for example, in the event of a haemorrhage in the body or with great exertion. This probably causes the side stitch that sometimes plagues us when we exercise.

The spleen throughout life

In unborn children, the spleen produces the blood cells. This function ceases typically after birth – the bone marrow then takes over the production of blood. However, if the blood cell production of the bone marrow is disturbed by a disease (e.g. leukaemia), the spleen can 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. That makes the spleen dispensable; you can survive without it. However, this may increase susceptibility to specific pathogens; for example, pneumococci seem more likely to trigger dangerous meningitis or pneumonia – vaccination then offers protection.