spleniculus

a large glandlike but ductless organ in the upper part of the abdominal cavity on the left side, lateral to the cardiac end of the stomach. Called also lien. adj., adj splen´ic. It is the largest collection of reticuloendothelial cells in the body and is composed of spongelike tissue of two types: red pulp, which is the dark reddish brown substance filling the interspaces of the sinuses of the spleen, and white pulp, which consists of sheaths of lymphatic tissue surrounding the arteries of the spleen. It is enclosed in a dense capsule. In a normal adult the spleen is about 12.5 cm long and weighs about 140 to 210 g. After gastric digestion and in the presence of disease the spleen enlarges.



During fetal life the spleen and liver produce erythrocytes, but after birth that function is taken over by the bone marrow. However, if there is bone marrow failure, the spleen may again produce erythrocytes. In the normal adult the spleen is a reservoir for blood, and contains a high concentration of erythrocytes. In times of exertion, emotional stress, pregnancy, severe bleeding, carbon monoxide poisoning, or other occasions when the oxygen content of the blood must be increased, the spleen contracts rhythmically to release its store of erythrocytes into the bloodstream.

The spleen also acts to help keep the blood free of unwanted substances, including wastes and infecting organisms. The blood is delivered to it by the splenic artery, and passes through smaller branch arteries into a network of channels lined with leukocytes known as phagocytes (see reticuloendothelial system). These clear the blood of old erythrocytes, damaged cells, parasites, and other toxic or foreign substances. Hemoglobin from the removed red cells is temporarily stored.