SPLEEN

Location: in upper left quadrant of the abdominal cavity.

Function:

Immune system functions

• Proliferation of lymphocytes
• Production of humoral antibodies
• Removal of macromolecular antigens from the blood

Hematopoietic functions

• Formation of blood cells during fetal life

• Removal and destruction of senile, damaged, and abnormal red blood cells

• Retrieval of the iron red cell hemoglobin
• Storage of blood, especially red blood cells, in some species.

Anatomic features

• Capsule of dense connective tissue with myofibroblasts from which trabeculae extends into the substance of organ.
• Hilum - provides for passage of the splenic artery and vein, nerves, and lymphatic vessels.
• Splenic circulation - splenic artery enter the white pulp as central artery and gives branches called marginal sinuses. In red pulp central artery continues into several penicillar arterioles, the latter - into capillaries sheathed by macrophages. They empty directly into the reticular meshwork of the cords or into the sinuses. The blood collected in the sinuses drains to trabecular veins that converge into larger veins and leaves the spleen by the splenic vein.

WHITE PULP

Functions: immune system functions, blood filtration and immune reactions to blood-borne antigens.

Composition:

• Reticular tissue with large amount of macrophages

    Function: a meshwork for lymphocytes

• Lymphatic nodules of B lymphocytes with central artery at eccentric position. Large secondary nodules are called splenic nodules or Malpighian corpuscles.
• Periarterial lymphatic sheath (PALS) with T lymphocytes as aggregates around the central artery in central position.

RED PULP

Function: hematopoietic functions, filtration and degradation of red blood cells

Composition:

• Splenic (venous) sinuses - special vessels lined by unusually shaped endothelial cells with only fragments of basal lamina. There are neither pericytes, nor smooth muscle cells. Processes of macrophages extend between the endothelial cells for monitoring the passing blood.
• Splenic cords (the cords of Billroth) - contain large numbers of erythrocytes, macrophages, lymphocytes, plasma cells, and granulocytes.