Spleen

At a glance

English

Spleen

Latin (TA2)

Lien

System

Lymphoid organ

Region

Trunk

Side

Single, on the midline

About the spleen

The spleen lies in the left hypochondrium, high and far back in the abdomen, tucked under the dome of the diaphragm and protected by the ninth to eleventh ribs. Its long axis follows the line of the tenth rib. A healthy adult spleen is soft, dark purple and about the size of a clenched fist: roughly twelve centimetres long, seven wide and three thick, though anything up to about fourteen centimetres is regarded as normal. It does not normally project below the left costal margin, so a spleen that can be felt there is enlarged.

It has two surfaces. The smooth, convex diaphragmatic surface faces up, back and laterally against the diaphragm, which separates it from the left pleura and lung. The visceral surface faces the abdominal organs and is moulded by them into impressions for the stomach in front, the left kidney behind and the left colic flexure below; the tail of the pancreas reaches it at the hilum. Its borders, superior and inferior, separate these surfaces, and the superior border characteristically has one or two notches. The organ is almost completely covered by peritoneum and is held by the gastrosplenic ligament to the stomach and the splenorenal ligament to the posterior wall.

Inside a thin fibrous capsule, trabeculae support a pulp of two kinds. Red pulp, the larger part, consists of venous sinuses and cords in which old or damaged red cells and platelets are trapped and broken down by macrophages, and their iron recovered. White pulp forms sheaths of lymphocytes around the arteries, with B-cell follicles, and mounts immune responses to antigens carried in the blood, especially encapsulated bacteria. In the fetus the spleen also makes blood cells.

Because it is so vascular, a blow to the left lower ribs can rupture the spleen and cause serious internal bleeding. It enlarges in infections such as glandular fever, in portal hypertension and in blood cancers, and an enlarged spleen is more easily torn. After splenectomy people remain prone to severe infections with pneumococci and similar organisms, so vaccination is advised. Small accessory spleens, often near the hilum, are common.

Function and supply

Function

Filters the blood, removing aged red cells and platelets and recycling their iron, and provides immune responses to blood-borne antigens; holds a small reserve of blood and platelets.

Nerve supply

Sympathetic fibres from the coeliac plexus forming a splenic plexus around the splenic artery, mainly controlling its vessels and capsule.

Blood supply

The splenic artery, the largest branch of the coeliac trunk, which divides into several branches at the hilum; the splenic vein joins the superior mesenteric vein behind the pancreas to form the hepatic portal vein.