spleen

The spleen is a soft, highly vascular organ about 12 cm long located in the left upper quadrant of the abdomen, beneath the diaphragm. It sits between the stomach and the left kidney and is connected to surrounding structures by the splenorenal and gastrosplenic ligaments. The splenic parenchyma consists of red pulp, which filters blood, and white pulp, which is involved in immune responses.

White pulp contains lymphocytes organized around central arteries, forming periarteriolar lymphoid sheaths and lymphoid follicles. Red pulp contains venous sinusoids and splenic cords where aging red blood cells are removed by macrophages. The spleen plays a role in defense against blood-borne pathogens, iron recycling, and storage of platelets, and it is especially important for responses to encapsulated bacteria.

Clinical notes: Splenomegaly arises in infections, liver disease, hematologic disorders, and malignancies. Splenic rupture after trauma is a medical emergency due to life-threatening hemorrhage. Removal of the spleen (splenectomy) reduces the body's ability to clear encapsulated organisms, increasing the risk of severe infection. Vaccination against Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitidis is recommended for people without a spleen. In some cases, spleen-preserving procedures are used to maintain function. Imaging with ultrasound or CT is commonly used to evaluate splenic disease.