The spleen consists of three types of tissue: white pulp, marginal zone and red pulp.

The white pulp: Primarily lymphatic tissue creating structures called germinal centres and the periarteriolar lymphoid sheath surrounded by the marginal zone.

• Germinal centres contain lymphocytes, macrophages and dendritic cells in direct contact with splenic arterioles.
• The periarteriolar lymphatic sheath consists of nodules containing mostly B lymphocytes. The spleen is required for maturation of B cells. The spleen also generates opsonins from enzymatic fragmentation of IgG

The marginal zone: surrounds the white pulp and consists of blood vessels, macrophages and B cells.

The red pulp: Vascular sinusoids separated by cords of tissue (cords of Billroth), containing specialized macrophages and forming a sponge-like region that functions as a filter for blood. Erythrocyte flow decreases as they pass through this area and and are removed from the circulation when they are damaged/old

Hypersplenism

Hyposplenism/asplenia