Filters the blood stream of foreign matter, including old and impaired blood cells, participates in immune response to blood borne antigens.

A major site of mononuclear phagocytic cells in the red pulp and of lymphoid cells in the white pulp.

The white pulp of the spleen provides immune function due to the lymphocytes that are housed there.

The spleen also consists of red pulp which is responsible for getting rid of aged red blood cells, as well as pathogens.

This is carried out by macrophages present in the red pulp. 

Weighs about 150 gm in the adult and is 12 cm in length, 7 cm in with and 3 cm in thickness.

Enclosed in a capsule.

Largest accumulation of lymphoid tissue in the body.

The main functions of the spleen are:

to produce immune cells to fight antigens

to remove particulate matter and aged blood cells, mainly red blood cells

to produce blood cells during fetal life.

The spleen synthesizes antibodies in its white pulp and removes antibody-coated bacteria and antibody-coated blood cells by way of blood and lymph node circulation. 

The spleen contains, in its reserve, half of the body’s monocytes within the red pulp, which upon moving to injured tissue turn into dendritic cells and macrophages while promoting tissue healing.

The spleen is a center of activity of the mononuclear phagocyte system.

The spleen is analogous to a large lymph node, as its absence causes a predisposition to certain infections. 

The spleen also is responsible for recycling some RBC components and discarding others. 

Hemoglobin is broken down in the spleen into amino acids that are reused.

Lies beneath the left hemidiaphragm and is attached to the diaphragm by the gastrosplenic, lienorenal, and phrenolienal ligaments.

Attached to the stomach and the left kidney.

Like the thymus, the spleen has only efferent lymphatic vessels.

Both the short gastric arteries and the splenic artery supply it with blood.

The germinal centers are supplied by arterioles called penicilliary radicles.

Accessory spleen is the most common splenic anomalies occurring in >1% of all patients.

Single or multiple accessory spleens can be found in the splenic hilum, pancreas, lesser sac, retroperitoneum, liver or intestinal mesentery.

White pulp, Malpighian follicles, seen on the cut surface of the spleen as gray specks consist of lymphoid cell aggregates surrounding medium sized splenic arteries.

The splenic vessels are surrounded by periarteriolar lymphatic sheath of T lymphocytes, which at intervals expand into lymphoid nodules composed of mainly of B lymphocytes.

With antigenic stimulation germinal centers form within B cell areas.

Arterial system terminates in fine arterioles enclosed within only a thin mantle of lymphocytes, which disappear as these vessels enter the red pulp.

Red pulp is traversed by vascular sinusoids, separate by Billroth cords.

Endothelial lining of the sinusoids is open between the sinusoids and cords.

Cords and consist of a labyrinth of macrophages connected through dendritic processes creating a physical and functional filter through which blood slowly seeps.

As blood traverses the red pulp it can take two routes to the splenic vein: a) flows through capillaries into the splenic cords, from which it filters out into the surrounding splenic sinudoids to reach the veins (open circulation or slow compartment) or b) blood passes from the capillaries directly to the splenic veins (closed circuit).

Only a small amount of blood enters the open route at any one time, but through a day the entire blood volume passes through the filtration system of the splenic cords, where it is exposed to the sinusoidal macrophages.

Splenic functions include the removal of unwanted elements of the blood via splenic phagoctosis in the splenic cords, immune function of antibody secreting plasma cells, a source of hematopoiesis and a sequester of formed blood elements.

Until the fifth month of prenatal development, the spleen creates red blood cells; after birth, the bone marrow is solely responsible for hematopoiesis. 

Macrophages of the spleen remove 1/120th of all red blood cells daily.

About 2 x 10 to the 11th red blood cells per day are removed from an adult, and about 50% of those cells are phagocytosed in the spleen.

Spleen phagocytes are very efficient in removing damaged red blood cells, white blood cells, and red blood cells with antibody coating and abnormal cells associated with hemolytic anemias.

Splenic sinusoids filter blood and allow mononuclear phagocytes to ingest circulating bacteria.

The spleen contains nearly half of the total B lymphocytes responsible for immunoglobulin production.

The spleen’s reticuloendothelial system retains the ability to produce lymphocytes. 

The spleen stores red blood cells and lymphocytes, and can store enough blood cells to help in an emergency. 

Up to 25% of lymphocytes can be stored at any one time.

Important for production of opsonizing antibodies, and this function is critical in clearance of encapsulated organisms.

As red blood cells pass from the cords to the the sinusoids the cells are deformed.

Red blood cell disorders with decreased elasticity can result in entrapment within the cords and lead to phagocytosis by cord macrophages.

Spleen macrophages can remove red blood cell inclusions , such as Heinz bodies, via the process pitting which neatly excises these abnormalities.

Splenic macrophages can remove particulate matter from the blood, including bacteria, cellular debris and abnormal macromolecules of inborn errors of metabolism, such as from Gaucher disease.

Dendritic cells in the periarterial lymphatic sheath can trap antigens which they then present to T cells.

T and B cells in the white pulp interact and generate antibody secreting plasma cells found mainly in the sinuses of the red pulp.

Hematopoiesis occurs in the fetus but stops at birth and can reactivated hematopoiesis can occur in the presence of severe anemia.

Due to the extensive vascularization and slow circulation the spleen, formed blood elements can sequester in the spleen.

The spleen lacks contractility in humans and the spleen can contain 30-40 cc of red blood cells, and this amount can increased signficantly with increasing spleen size.

The spleen stores about 30-40% of the total platelet mass in the body, and up to 80-90% of platelet total mass can be sequestered in the interstices of the red pulp with splenomegaly.

An enlarged spleen can trap leukocytes and cause leukopenia.

In the presence of splenic auto infarction or splenectomy there is an increased risk for disseminated infection with encapsulated bacteria such as pneumococcus, meningococcus an Hemophilus influenzae.

Deficient spleen function results in reduced filtering ability and antibody production contributing to increased risk of infection and often fatal sepsis.

Asplenia and hyposplenism are known risk factors for overwhelming infection by encapsulated bacteria.

Common causes of calcification are histoplasmosis, tuberculosis and brucellosis.

Spontaneous rupture can rarely occur with leukemia with about 40 reported cases, and fewer than half related to acute myelogenous leukemia.

Spontaneous rupture of spleen not necessarily associated with splenomegaly.

Splenic rupture associated with abdominal pain, nausea, vomiting and left shoulder pain (Kehr’s sign).

100% mortality for spontaneous splenic rupture without splenectomy.

Ruptured spleen can be managed conservatively or with surgery.

Ruptured spleen with hemodynamic instability requires surgery, as does the presence of splenic disease, hemoperitoneum or grade 3 or higher American Association for the Surgery of Trauma Splenic Injury Scale.

The elderly and young with splenic rupture benefit from early surgery.

Rupture of the spleen requiring more than one unit of blood associated with a high risk of failure for conservative management.

Stable patients with closed, subscapular splenic hematomas can be treated conservatively.

Stable patients with closed, subscapular splenic hematomas can be treated with splenic embolization.

Splenic infarctiion may be associated a with a left upper quadrant pain, left flank pain, or both and a significant number of patients may have no symptoms (Antopolsky M et al).

Splenic infarction is usually associated with elevated LDH levels, and about one fourth of patients have fever and chills.

Splenic infarction may be associated with EB virus infections.

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