The spleen, a small organ located in the upper left side of the abdomen, is an integral component of the lymphatic system. Positioned just above the stomach and protected by the lower rib cage, this organ performs several functions. Its roles range from managing blood components to supporting the body’s defense mechanisms.
Spleen’s Structure and General Roles
The spleen is about the size of a fist in adults, with a distinctive purple color. Blood enters through the splenic artery and exits via the splenic vein.
Internally, the spleen is divided into two primary tissue types: the red pulp and the white pulp. The red pulp, making up approximately 80% of the spleen, contains venous sinuses and splenic cords rich in macrophages. Its main functions include filtering blood by removing old, damaged, or abnormal red blood cells and acting as a reservoir for blood and platelets. This filtering process is achieved as healthy cells pass through narrow slits in the venous sinuses, while unhealthy ones are retained and broken down by macrophages. The spleen also recycles iron from these broken-down red blood cells, returning it to the bone marrow for new hemoglobin production.
How the Spleen Defends the Body
The white pulp of the spleen is specialized for immune function, housing lymphocytes and macrophages. This tissue is organized around arteries and serves as a site for immune responses against blood-borne pathogens.
Lymphocytes, specifically T cells and B cells, are present in the white pulp and are activated by antigens, which are foreign substances like bacteria or viruses, filtered from the blood. Macrophages and dendritic cells in the spleen filter antigens from the bloodstream and present them to T cells, initiating an immune response. Activated T cells then coordinate further immune activity, including activating B cells. B cells, upon recognizing antigens, produce antibodies that help eliminate pathogens. This process is particularly important for responding to encapsulated bacteria, which have smooth surfaces that make them difficult for other immune cells to target directly. The spleen also produces cytokines, signaling molecules that regulate and coordinate the immune response by promoting or inhibiting the activity of immune cells.
Common Spleen Health Issues
Several conditions can affect the spleen’s health, impacting its ability to perform its roles in blood filtration and immune defense. Splenomegaly, or an enlarged spleen, is a common issue. Infections like mononucleosis, certain liver diseases such as cirrhosis, and blood disorders like leukemia or lymphoma can all lead to spleen enlargement. When enlarged, the spleen may become more fragile and less efficient.
Another serious condition is splenic rupture, which often occurs due to direct abdominal trauma. A ruptured spleen can cause significant internal bleeding and is considered a medical emergency.
Certain medical conditions, like sickle cell anemia, can also affect the spleen. In sickle cell anemia, the abnormal red blood cells can clog the spleen’s blood vessels, leading to damage and reduced function.
Life After Spleen Removal
When the spleen is removed, a procedure known as a splenectomy, the body loses an organ with important functions in immunity and blood filtration. Individuals without a spleen face an increased risk of certain infections, particularly those caused by encapsulated bacteria such as Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. This heightened susceptibility is due to the spleen’s unique role in identifying and clearing these specific types of pathogens from the bloodstream.
To mitigate this risk, individuals who have undergone a splenectomy are advised to receive specific vaccinations to protect against these bacteria. They may also need to take antibiotics as a preventive measure when necessary. While the liver and bone marrow can take over some of the spleen’s filtering and blood cell storage functions, they cannot fully compensate for its specialized immune responses, especially against encapsulated bacteria. Therefore, lifelong precautions are necessary to manage the increased infection risk.