Human spleen: anatomy, immune functions, and clinical significance

Anatomy

The spleen is typically fist-sized in adults and lies posterior to the stomach on the left. Internally it has two main tissue types: white pulp, rich in lymphocytes, and red pulp, which filters blood and removes old or damaged blood cells. Blood enters the spleen through the splenic artery and leaves via the splenic vein, which connects to the portal circulation.

Functions

• Immune surveillance: lymphocytes and other immune cells in the spleen detect and respond to blood-borne pathogens, helping the body fight infections.
• Blood filtration: the spleen removes aged or abnormal red blood cells and recycles iron.
• Storage: it can hold a reserve of platelets and some blood that can be released in times of need.
• Hematopoiesis in development: during fetal life the spleen contributes to the formation of blood cells.

Clinical significance

The spleen can enlarge (splenomegaly) in a variety of conditions, including infections, liver disease, and blood disorders. It is vulnerable to injury in blunt abdominal trauma, and a ruptured spleen can cause dangerous internal bleeding. Surgical removal of the spleen (splenectomy) is sometimes necessary; people without a spleen have an increased risk of severe bacterial infections, particularly from encapsulated organisms, and are often advised to receive specific vaccinations and preventive antibiotics in certain situations.

Additional notes

Some individuals have accessory (extra) spleens, which are usually small and harmless. Although the spleen performs important functions, it is not absolutely essential for survival; other organs and systems can compensate for many of its roles, especially when appropriate medical measures are taken after splenectomy.