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Spleen

Synonym: splen, lien
German: Milz

1 Definition

The spleen is the largest lymphatic organ in the human body.

2 Anatomy

The spleen is located intraperitoneally in the regio epigastrica sinistra in the upper left quadrant in the so-called splenic niche. The base of the spleen is located at the left of the diaphragmaticdome. The arteria splenica, a branch of the truncus coeliacus is responsible for arterial vascular supply to the spleen. Venous drainage occurs via the vena splenica (vena lienalis), which empties into the vena portae (portal vein). Both vessels form the spleen's vascular pedicle (splenic hilum).

A normal spleen has an organ weight of approx. 150 to 200 grams. The length of the organ is around 12-13 cm, with a width of 7-8 cm and an organ thickness of around 3 cm.

Innervation of the spleen is via parasympathetic and sympathetic fibres from the celiac plexus, from which the splenic artery accompanies them to the spleen. Visceral sensitive and vasomotoric branches with adrenergic nerve fibers guide the contractions of the spleen's trabecular capsule system through myofibroblasts.

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2.1 Embryology

The spleen develops from a proliferation of the mesenchyme between both peritoneal leaves of the mesogastrium dorsale. Through gastric torsion, it ultimately passes intraperitoneally into the left upper abdomen.

2.2 Accessory spleen

Alongside the 'main spleen', sometimes one or more accessory spleens (splen accessorius) can be found as an anatomical variant. They are usually localised near to the splenic hilum, on the tail portion of the pancreas. They are then embedded there in the ligamentum gastrosplenicum or the omentum majus and have the same histological appearance as the main organ. If there is an indication for a splenectomy, then they can be clinically relevant. If the spleen has to be removed e.g. due to anaemia (as a result of producing an excess of red blood cells), any accessory spleens present must also be removed. On the other hand, if the spleen has to be removed e.g. due to a rupture, then the accessory spleen can take over its function, so that there is no resulting immune system weakness.

2.3 Ligamentous apparatus

The spleen is essentially fixed by 4 ligaments, peritoneal duplication of:

3 Histology

On the outside, the spleen is surrounded by a tight connective tissue capsule, which is covered by the peritoneum. Reticulum cells and myofibroblasts in the form of trabeculae extend from the capsule into the parenchyma, and in this way build a three-dimensional meshwork.

The actual splenic parenchyma is structured into 2 different sections, the white and the red pulp.

4 Function

The spleen fulfils a multitude of tasks in the area of immune response and cell turnover.

Ageing or deformed, i.e. membrane damaged or enzyme defective blood cells, such as erythrocytes and platelets are phagocytosed by macrophages from the red pulp. The same is true for microorganisms or immunocomplexes or fibrin monomers circulating in the blood.

In the periarteriolar lymph sheaths and lymph follicles of the white pulp, antigen-induced differentiation and proliferation of B-lymphocytes and T-lymphocytes occurs.

The spleen is involved in extramedullary haematopoiesis until the sixth year of life. In certain bone marrow diseases the spleen remains the location for haematopoiesis until later years.

5 Clinic

5.1 Diseases

An overactive spleen is referred to as hypersplenism, and an under-functioning spleen as hyposplenism. If a spleen is enlarged, this is referred to as splenomegalia. An important traumatic incident is a ruptured spleen.

5.2 Methods of examination

In healthy individuals the spleen is not palpable. In cases where there is notable enlargement, it is palpable during inspiration under the left costal arch. Examination of the spleen takes place using imaging techniques e.g. with:

The splenic vessels can be viewed angiographically, and morphological, topographical and functional changes using splenic szintigraphy.

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