Spleen: Encyclopedia II - Spleen - Anatomy

Spleen - Anatomy

It is an organ derived from mesenchyme and lying in the mesentery. The organ consists of masses of lymphoid tissue of granular appearance located around fine terminal branches of veins and arteries. These vessels are connected through the splenic pulp by modified capillaries called splenic sinuses. Cross sections of the spleen reveal a red soft surface which is divided into red and white pulp. Red pulp corresponds to the sinuses which are usually filled with blood. The white pulp shows white nodules, called Malpighian corpuscles. Under the microscope, these areas correspond to lymphoid follicles, rich in B-lymphocytes, and the periarteriolar lymphoid sheaths, rich in T-lymphocytes.

The human spleen is located in the upper left part of the abdomen, behind the stomach and just below the diaphragm. In a normal individual this organ measures about 125 × 75 × 50 mm (5 × 3 × 2 in) in size.

In certain animals such as dogs and horses, the spleen sequesters a large number of erythrocytes (red blood cells), which can be dumped into the bloodstream during periods of physical exertion. These animals also have large hearts in relation to their body size to accommodate the higher-viscosity blood that results. Some athletes have tried doping themselves with their own stored red blood cells to try to achieve the same effect, but the human heart is not equipped to handle the higher-viscosity blood.

Approximately 10% of people have one or more accessory spleens. They may form near the hilum of the main spleen, the junction at which the splenic vessels enter and leave the organ.

Adapted from the Wikipedia article "Anatomy", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki