Red pulp

Red pulp
Transverse section of a portion of the spleen. (Spleen pulp labeled at lower right.)
Spleen
Details
Identifiers
Latin	pulpa splenica
Dorlands /Elsevier	p_41/12679479
FMA	15844
Anatomical terminology []

The red pulp of the spleen is composed of connective tissue known as the cords of Billroth and many splenic sinuses that are engorged with blood, giving it a red color. Its primary function is to filter the blood of antigens, microorganisms, and defective or worn-out red blood cells.

The spleen is made of red pulp and white pulp, separated by the marginal zone; 76-79% of a normal spleen is red pulp. Unlike white pulp, which mainly contains lymphocytes such as T cells, red pulp is made up of several different types of blood cells, including platelets, granulocytes, red blood cells, and plasma.

The splenic sinuses of the spleen, also known as sinusoids, are wide vessels that drain into trabecular veins. Gaps in the endothelium lining the sinusoids mechanically filter blood cells as they enter the spleen. Worn-out or abnormal red cells attempting to squeeze through the narrow intercellular spaces become badly damaged, and are subsequently devoured by macrophages in the red pulp. In addition to aged red blood cells, the sinusoids also filter out particles that could clutter up the bloodstream, such as nuclear remnants, platelets, or denatured hemoglobin.

Red pulp consists of a dense network of fine reticular fiber, continuous with those of the splenic trabeculae, to which are applied flat, branching cells. The meshes of the reticulum are filled with blood:

In lymphoid leukemia, the white pulp of the spleen hypertrophies and the red pulp shrinks. In some cases the white pulp can swell to 50% of the total volume of the spleen. In myeloid leukemia, the white pulp atrophies and the red pulp expands.