Spleen

About the size of a cupped hand. Intraperitoneal, in the left upper quadrant.

Largest lymphoid organ – lymphoid organs consist of the thymus, lymph nodes, spleen and are part of the immune system.

Anatomy

Relations – Posteriorly: left diaphragm, left lung, ribs 9-11. Anteriorly: stomach. Inferiorly: splenic flexure of colon. Medially: left kidney.

Structure – Entirely surrounded by peritoneum except hilum, where splenic branches of splenic artery and vein enter and leave. Lymphoid follicles found in white pulp, which is scattered in the red pulp that constitutes most of its substance. White pulp – lymphocytes form lymphoid follicles which are visible to the naked eye as whitish nodules.

Physiology

Act as specific blood reservoirs to contribute up to 100ml of blood. This is done in 2 places: venous sinuses and red pulp. Venous sinuses: act just like any other venous sinus to store whole blood. Red pulp: capillaries are permeable to red blood cells which ooze out into trabeculae, in which they are trapped – reservoir of concentrated red blood cells. Sympathetic nervous system activation causes spleen to contract and may raise haematocrit 1 to 2 percent.

White pulp – lymphoid cells manufactured, similar to lymph nodes.

As red blood cells are filtered out into the trabeculae in red pulp, the fragile ones rupture due to trauma and haemoglobin and cell stroma are digested by reticuloendothelial cells to be reused as nutrients for making new blood cells.

Reticuloendothelial cells – phagocytic cells part of cleaning system for blood, acting in concert with similar cells in venous sinuses of liver. Remove debris, bacteria, parasites etc.

Pathology

Congenital polysplenia, asplenia. Associated with other malformations, especially of cardiovascular system.

Splenomegaly – often with chronic infection. Spleen enlarges same way as lymph nodes. Cleansing function increased. May also be due to congestion caused by raised splenic venous blood pressure, neoplasms (eg. lymphoma, leukaemia), immune and storage disorders.

Infarction – pale infarcts. Due to emboli, thrombosis (eg. with sickle cell disease).

Rupture – often due to blunt abdominal trauma (eg. automobile accidents). Massive intraperitoneal haemorrhage. Emergency splenectomy.

Atrophy – due to multiple infarcts, intestinal malabsorption states (eg. coeliac disease).

Surgery

Spenectomy – removal of spleen.

Subtotal (partial) splenectomy – removal of one or more segments.

Often performed to prevent patient from bleeding to death. Does not usually produce serious side effects, especially in adults because most of its functions assumed by other reticuloendothelial organs (eg. liver, bone marrow). Greater susceptibility to infections.