spleen
Meaning of spleen: A fist-sized filter tucked under the left ribs, sorting worn-out blood cells from good ones and screening blood for infection.
Definition of spleen
The spleen is a soft, dark red organ about the size of a fist, lying under the left lower ribs behind the stomach. It filters blood rather than lymph, pulling out worn-out red cells and returning their iron for reuse. It also holds a large population of immune cells that detect bacteria in the bloodstream. Life is possible without it, but with a lasting cost in infection risk.
What does it actually do?
Two distinct tissues sit side by side inside it. The red pulp is a maze of narrow channels that blood must squeeze through. Young flexible red cells pass easily; stiff, aged or damaged ones cannot, and are broken down on the spot. The white pulp is packed with lymphocytes arranged around small arteries, sampling blood as it flows past for signs of infection. The spleen also stores platelets and can release them, and in a fetus it makes blood cells outright, a capacity that can reawaken in adults when the marrow fails.
Why does losing it matter?
The white pulp is the body's main site for mounting a response to bacteria wrapped in a sugar capsule, which hides them from other defenses. Without a spleen, those organisms can multiply in the bloodstream with little to slow them, and an infection that would have been trivial can become life threatening within hours.
| Consequence of removal | Detail |
|---|---|
| Vulnerability to capsulated bacteria | Pneumococcus, meningococcus, Haemophilus influenzae type b |
| Vaccination programs | Given in advance where surgery is planned |
| Blood film changes | Odd shaped red cells and nuclear remnants persist |
| Platelet count | Often rises after removal |
What makes it enlarge or rupture?
Because it is a filter, anything that increases the workload swells it: infections such as glandular fever and malaria, blood disorders in which cells are destroyed faster than usual, leukemia and lymphoma, and back pressure from a scarred liver. A normal spleen is protected by the rib cage, but an enlarged one extends below them and is exposed. It is the organ most often torn in blunt abdominal injury, and because it holds a great deal of blood at any moment, a tear can bleed heavily into the abdomen.
Is it part of the lymphatic system?
Yes. It is the largest organ of the lymphatic system, though it differs from lymph nodes in one respect that defines its role: nodes filter lymph, while the spleen filters blood directly. That is why it is positioned on a major artery rather than along a lymph channel.
Used in a sentence
Imaging after the collision showed a grade three laceration of the spleen with contained bleeding.
Good to know
Loss of the spleen leaves a lasting vulnerability to bacteria with a sugar capsule, and an enlarged spleen extends beyond the protection of the rib cage and is more easily torn.
Word origin
Where “spleen” comes from
From the Greek splen, the name of the organ, which survives in words such as splenectomy and splenomegaly.