The spleen is a fist-sized organ situated in the upper abdomen. It does not play a role in the chemical breakdown or mechanical movement of food, meaning it is not a digestive organ. While its name is sometimes associated with digestive concepts in traditional medical systems, in modern physiology, the spleen is entirely separate from the gastrointestinal tract. This abdominal organ is instead a highly specialized component of the circulatory and immune systems, performing functions related to blood health and defense against pathogens.
Core Functions: Blood Filtration and Immune Response
The spleen performs two major functions maintained by its distinct internal structure of red pulp and white pulp. The red pulp is dedicated primarily to the hematological role of filtering blood, a process described as the “graveyard of red blood cells.” Blood flowing through the red pulp’s network of specialized vessels, called sinusoids, is monitored by stationary white blood cells called macrophages. These macrophages identify and engulf old, damaged, or rigid red blood cells (RBCs) that have reached the end of their approximately 120-day lifespan.
This filtration process allows the spleen to efficiently recycle essential components, such as iron, back into the body for the production of new red blood cells in the bone marrow. The spleen also acts as a reservoir, storing a supply of platelets and a reserve of blood volume that can be released into circulation during times of hemorrhagic shock or injury.
The white pulp focuses entirely on immunological defense, operating much like a large, specialized lymph node. It is populated with lymphocytes, including B cells and T cells, which monitor the blood for foreign invaders such as bacteria, viruses, and other antigens. When pathogens are detected in the bloodstream, the white pulp initiates an adaptive immune response, generating antibodies and activating immune cells to neutralize the threat. This function is particularly important for mounting a defense against encapsulated bacteria, which are organisms surrounded by a smooth, protective coating.
Why the Spleen is Often Confused with Digestive Organs
The anatomical positioning of the spleen is the primary reason for confusion regarding its function. The organ sits in the upper left quadrant of the abdomen, protected by the lower ribs, in close proximity to several major digestive structures. It tucks snugly against the posterior wall of the stomach, and its vascular connections are closely linked to those supplying the stomach and the tail of the pancreas.
The spleen is connected to the stomach by the gastrosplenic ligament, and it shares a blood supply with organs of the upper digestive tract via the celiac trunk artery. Because the spleen is positioned directly next to the stomach, left kidney, and pancreas, discomfort or pain originating from any of these digestive organs can sometimes be mistakenly attributed to the spleen. Additionally, historical medical traditions, such as Traditional Chinese Medicine, conceptually linked the spleen to the digestive system, further perpetuating the misconception.
Life Without a Spleen: Post-Splenectomy Considerations
Although the spleen performs significant functions, the human body can adapt and survive without it, a condition that occurs after a splenectomy. Following the procedure, other organs, most notably the liver and bone marrow, take over the function of filtering old red blood cells from the circulation. However, the most consequential change is a lifelong elevation in the risk of serious infection, particularly from the encapsulated bacteria that the spleen was uniquely suited to eliminate.
The absence of the spleen makes individuals more susceptible to overwhelming post-splenectomy infection (OPSI), a severe and rapidly progressing illness caused by organisms like Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitidis. To mitigate this increased vulnerability, specific medical precautions are required for the rest of an individual’s life. Patients must receive specialized vaccinations, including the Pneumococcal, Meningococcal, and Haemophilus influenzae type b (Hib) vaccines, often with periodic booster doses. Many people are also advised to keep a course of emergency broad-spectrum antibiotics on hand to be taken immediately at the first sign of a fever or other possible infection.