Introduction
The spleen is an organ that is connected to the bloodstream and is counted among the lymphatic organs. It performs important tasks in the area of blood purification and immune defence. During the embryonic period, in unborn children, the spleen is involved in blood formation. If the spleen has to be removed, for example due to a serious accident, other lymphatic organs can take over the function and tasks.
Tasks of the spleen
The spleen has important functions. It plays a decisive role in the immune system and blood purification and moulting. The white pulp of the spleen contains the white blood cells, T and B lymphocytes, dendritic cells and macrophages (scavenger cells).
Here, the spleen looks for and fights against intruders, so to speak. In the red pulp of the spleen there is a special parenchyma (tissue) that serves a purifying blood moult. Here, non-functional red blood cells are removed from the blood and broken down.
A further task of the spleen is blood storage. The spleen is responsible for ensuring a permanent supply of important blood cells. These include the red blood cells (erythrocytes), white blood cells (lymphocytes) and blood platelets (thrombocytes).
If necessary, it should be possible to supply sufficient blood cells through the spleen. Furthermore, during the embryonic period, i.e. in unborn children, the spleen is a place where blood is formed, along with other organs such as the liver and bone marrow. Until about the age of six, the spleen, as the place of formation of mainly red blood cells, remains involved in blood formation.
Functions of the spleen
The spleen is an organ that is anatomically divided into a red pulp and a white pulp. The special term pulp describes the spleen’s medulla. The red and white pulp have different functions.
While the red pulp is responsible for blood cell moulting, the white pulp serves as a lymphatic organ for immunological monitoring of the blood, like a kind of filter station. This means that the two essential tasks of the spleen take place in two functionally different compartments. The red pulp of the spleen makes up about seventy-five percent of the spleen tissue and consists of net-like pulp strands (medullary strands) as well as tiny blood vessels, venous sinusoids, which run between the pulp strands.
The red splenic pulp is thus connected to the bloodstream. The reticular tissue of the red pulp is used for cell migration. This means that overaged blood cells, especially red blood cells, are filtered out and broken down here.
The red blood cells give the red pulp its color and name. Red blood cells, erythrocytes, survive for about one hundred and twenty days in the blood. During their life cycle, they flow several times through the spleen and undergo a blood moult.
Young erythrocytes are deformable and can move easily through the meshes of the red pulp, while old erythrocytes are less deformable and get caught in the meshes of the spleen. The old erythrocytes are then broken down by so-called scavenger cells, macrophages. Erythrocytes flow through the red pulp over and over again until one day they are too old and can no longer pass through the tissue well enough and are broken down.
The white pulp makes up the remaining twenty-five percent of the spleen tissue. The white pulp is crucial for the immune system. The white pulp gets its color and name from the white blood cells, lymphocytes, which are formed here, mature and are finally stored.
So-called T lymphocytes and dendritic cells form sheaths around small arterial vessels. These complexes are called periarterial lymphatic sheaths (PALS). B lymphocytes are arranged follicularly on the PALS and the immune cells form the white pulp of the spleen in their entirety.
Functional dendritic cells are there to monitor the blood that flows through the spleen. When they find particles of potential pathogens, called antigens, they take them up and present them on their cell surface. This activates T lymphocytes and eventually B lymphocytes as well.
The B-lymphocytes then multiply and form antibodies matching the antigens. These bind to each other and the complexes are broken down by macrophages. In this way, pathogens in the blood can be destroyed. Thus, the white pulp of the spleen fulfils an important function of the immune defence.
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