The spleen is the largest single mass of lymphoid tissue in the body. Located in the left upper quadrant of the abdominal cavity, specifically in the left hypochondriac region, it sits snugly beneath the diaphragm and posterior to the stomach. Because of its protected position behind the lower ribs, it is normally not palpable in healthy adults.
Measuring roughly 12 centimeters in length, the spleen is richly vascularized, receiving blood directly from the splenic artery, a major branch of the celiac trunk. Its external surface is covered by a fibroelastic capsule that extends inward as trabeculae, creating a supportive framework for the soft pulp inside.
Internally, the splenic tissue is divided into two distinct regions known as the white pulp and the red pulp.
As blood flows through the red pulp, it encounters narrow passages and slits that older, fragile red blood cells struggle to squeeze through. Fixed macrophages patrolling these channels capture and destroy damaged, rigid, or aged erythrocytes through phagocytosis.
Beyond simply destroying old cells, the spleen salvages useful components. Iron from hemoglobin is extracted and recycled back to the bone marrow via the bloodstream, while the remaining heme is broken down into bilirubin and sent to the liver for excretion.
The spleen acts as a giant lymph node for the blood stream. When blood-borne antigens enter the white pulp, T-lymphocytes and B-lymphocytes come into contact with them. This triggers antigen presentation, clonal expansion, and the production of specific antibodies.
Because the blood is filtered directly through this immune tissue, the spleen is especially critical for defending the body against encapsulated bacteria like *Streptococcus pneumoniae* and *Neisseria meningitidis*.
In addition to filtering red blood cells, the spleen serves as a reservoir for platelets, holding up to one-third of the body's total platelet reserve ready for release during acute hemorrhage.
While the spleen produces blood cells (hematopoiesis) during fetal development, it stops this function after birth. However, in certain severe pathological states where the bone marrow fails, the adult spleen can resume hematopoiesis to support blood cell production.
Because the spleen is fragile and highly vascular, blunt force trauma to the left upper abdomen can easily cause a splenic rupture, leading to severe internal hemorrhage and life-threatening shock.
When a ruptured spleen cannot be repaired, surgeons perform a splenectomy. While patients can live without a spleen, they face a lifelong increased risk of overwhelming post-splenectomy infection (OPSI). Midwives and healthcare providers must ensure these individuals understand the importance of prompt antibiotic therapy at the first sign of fever.