Spleen

Function

The spleen is the blood's filter and its immune roundabout. Red pulp cords and sinuses cull aged red cells — recycling their iron — while white pulp follicles mount antibody responses to encapsulated bacteria carried in the blood. About a third of the body's platelets pool in it at any moment, ready for release.

It follows ribs 9–11 posteriorly ('the 1, 3, 5, 7, 9–11 rule': 1×3×5 inches, 7 oz, ribs 9–11), making it the abdomen's most commonly injured organ in blunt trauma — a ruptured spleen can bleed massively, sometimes after a delay while blood collects under its capsule.

Blood supply

Splenic artery from the coeliac trunk; splenic vein joins the SMV to form the portal vein.

Nerve supply

Sympathetic from the coeliac plexus; blood irritating the left hemidiaphragm refers pain to the left shoulder via the phrenic nerve (Kehr's sign).

Clinical relevance

Splenic rupture

Left lower rib trauma plus hypotension demands a fast scan — delayed capsular rupture can occur days after injury.

Splenomegaly

Portal hypertension, blood cancers and haemolysis swell it; massive spleens risk spontaneous rupture.

Post-splenectomy sepsis (OPSI)

Without the spleen, encapsulated organisms overwhelm — vaccination against pneumococcus, meningococcus and Hib is lifelong insurance.

Related conditions

• Cirrhosis
• Sickle cell disease
• Lymphoma
• Thalassaemia
• Malaria