Spleen – Structure & Function

Overview 

The spleen is a sizeable bean-shaped organ underneath the diaphragm on the left side of the body. The spleen comprises T and B lymphocytes and many phagocytes and is an integral part of the mononuclear phagocyte system. 

Although the structure of the spleen looks like that of the large lymph nodes, the spleen varies from a lymph node in possessing no lymphatic drainage and comprising large numbers of red cells. 

Structure of Spleen 

The spleen is a dark purple-coloured organ positioned in the left hypochondriac area of the abdomen, connecting the stomach and diaphragm fundus. 

It differs in size and weight during an individual’s lifespan, but in an adult, it usually is about 12 cm long, 8cm broad and 3-4 cm thick, weighing close to 200. 

The spleen contains diaphragmatic and visceral surfaces. The diaphragmatic surface is in touch with the inner surface of the diaphragm. 

The spleen has an exterior peritoneum coat, which firmly clings to the internal fibro-elastic coat or splenic capsule that dips into the organ, creating trabeculae. 

The spleen has a spongy interior known as splenic pulp. The splenic pulps are of two types: 

White Pulp

It has periarteriolar sheaths of lymphatic tissue with enlargements called splenic lymphatic follicles comprising rounded masses of lymphocytes. 

These follicles are the base of lymphocyte production, called primary lymphoid follicles, which are constituted primarily of follicular dendritic cells (FDC) and B cells. 

They are visible to the human eye on the freshly cut surface of the spleen as whitish dots against the dark red backdrop of red pulp. 

The white pulp forms islands’ within a meshwork of reticular fibres containing red blood cells, macrophages and plasma cells (red pulp). 

It functions in a manner analogous to the nodules of the lymph node. The primary function of the red pulp is to phagocytize old red blood cells. 

Red Pulp

It has numerous sinusoids comprised of blood, divided by a network of perivascular tissue called the splenic cords. 

The splenic cords have numerous macrophages and are the site of intense phagocyte activity. 

They also have numerous lymphocytes, which are derived from the white pulp. 

The red pulp has a specific role besides filtration. It is the body’s primary site of the destruction of RBCs, which generally have a life span of only 120 days. Degenerate red cells are eliminated from the circulation in the spleen, and the haemoglobin they carry is degraded to an excretable pigment and an iron molecule that is recycled (i.e., used to generate new haemoglobin somewhere). 

Functions 

• The spleen contains infection-fighting white blood cells, which fight against the infecting germs in the blood.  
• It manages the level of blood cells. The spleen regulates the level of white blood cells (WBCs), red blood cells (RBCs) and platelets (small cells that create blood clots). 
• It screens the blood and eliminates the old or damaged red blood cells. The red blood cells must pass through narrow passages. The healthy blood cells can go through the spleen and continue circulating throughout the bloodstream, but the cells that can’t pass the test will be broken down in your spleen by macrophages. 
• If the spleen doesn’t work in a good order, it may start to remove healthy blood cells. This situation, in turn, leads to anaemia, an increased risk of infection, bleeding or bruising. 

Disorders of Spleen 

The disorders of the spleen include: 

Splenomegaly (enlarged spleen) 

Different disorders can cause the spleen to enlarge, at times to 2kg or more. Any conditions that drive a rapid breakdown of blood cells, like haemolytic anaemias, can significantly strain and enlarge the spleen.

Other causes of splenomegaly include infections glandular fever), liver disease and a few cancers (such as leukaemia, Hodgkin’s disease, and lymphoma). 

Hypersplenism 

Hypersplenism is a hyperactive spleen. When the spleen is hyperactive, it eliminates the blood cells too prematurely and too rapidly. A hyperactive spleen is frequently, but not always, enlarged (splenomegaly). 

Other Spleen Disorders 

• Blood disorders 
• Cancers – solid organ, blood 
• Cysts and tumours 
• Splenic rupture (traumatic/atraumatic). 
• CAS, Congenital absence of the spleen 

Diagnosis of spleen disorders 

Spleen can be diagnosed using several tests, including blood tests, computed tomography (CT) scan, bone marrow biopsy, physical examination, ultrasound and MRI or PET scan. 

Treatment for spleen disorders 

Treatment is based on the disorder and its particular cause. For example, if splenomegaly is caused by specific cancers (like Hodgkin’s disease, leukaemia or lymphoma), treatment will focus on controlling the primary disease. 

Hypersplenism is caused by cirrhosis of the liver and can be treated with abstinence from alcohol and special dietary modifications. A badly ruptured spleen is usually surgically removed. 

Conclusion

The spleen plays a vital role in your immune system response. When it finds bacteria, viruses, or other germs in your blood, it generates white blood cells, called lymphocytes, to fight against the infections they cause. 

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