The spleen is an organ found in most vertebrate animals which serves as a site of red blood cell storage, immune cell monitoring of the blood, and degradation of old red blood cells. The spleen is divided into several sections which have specialized functions, most notably the white pulp and the red pulp. While the spleen is a very important organ for blood storage and for normal immune responses to infections of the bloodstream, the spleen is not an essential organ. If a person loses their spleen due to damage or infection then they can still survive and lead a relatively normal life. They will still require careful observation and will be at additional risk from certain kinds of infections, but on the whole they will not be negatively impacted by their splenectomy on a daily basis.

Red Pulp

The red pulp is one of the two main divisions that compose the spleen and define its form and function. As the name suggests the red pulp is composed primarily of red blood cells, and it comprises the majority of the spleen by weight, which is why the spleen appears as a large blood red organ when examined with the eyes. The red pulp both serves as a storage site to buffer the body's normal levels of blood, and as a site for the destruction of old blood that the body no longer wants or requires. Many damaged blood cells in the red pulp are degraded by the immune cells known as macrophages, as the heme molecule contained within these cells is toxic and must be properly degraded to prevent acute injury to the host. These macrophages target the damaged cells and cause them to die so that the macrophages (white blood cells) can engulf the cells and effectively “eat” them, thus disposing of them in a careful and controlled fashion. Cells in the red pulp can also serve as a blood reserve in case of injury at another part of the body, increasing the amount of time an individual can survive following injury and boosting respiratory rate following blood loss.

White Pulp

The white pulp is primarily composed of white blood cells which make up the majority of the classical immune system, which actively filter the blood moving through the body. These cells monitor passing blood for signs of inflammation of pathogenicity, which they are able to detect using special cellular sensory molecules known as pattern recognition receptors. If a pathogen is detected in the blood, then white blood cells in the white pulp that recognize that pathogen will begin to multiply, forming a rapidly dividing structure known as a germinal center which is often structurally similar to a lymphoma. This germinal center is composed of T Cells and B Cells, as well as antigen presenting cells such as dendritic cells which were the cells to first detect signs of infection. After dividing for several days, the germinal center will produce large amounts of antibodies specific to the invading pathogen. These antibodies can then target the invading pathogen, and they will target it for direct damage and for engulfment by macrophages and other similar cells of the immune system. This will allow the immune system to clear the microbes from the blood, restoring the original healthy state of the host. After infections are resolved, germinal centers will reduce in size and will eventually disappear, although they will still leave behind functional white blood cells that will prevent recurrent infections with the pathogen that they first detected.


While the spleen is important for normal immune function and red blood cell degradation, it is not essential for survival and in certain individuals it may rupture or be removed surgically in a splenecomy operation. Reasons for splenectomy include splenic rupture (as may occur in individuals suffering from acute mononucleosis) and cancer affecting the spleen. Individuals without a spleen may be at an elevated risk for certain bloodborne diseases, and may be more likely to die from ischemic injury due to a lack of blood cell reserves, however they may otherwise live normal lives.


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