Facts About the Spleen
The spleen is the largest reticuloendothelial organ in the body and arises from the primitive mesoderm by the 5th week of gestation. 1, 2
Anatomical Development and Structure
- The spleen develops from the primitive mesoderm during embryonic development 1
- The spleen is evident in the embryo by the 5th week of gestation 1
- It is the largest reticuloendothelial organ in the body, playing a crucial role in immune function and blood filtration 1, 2
Primary Functions
- The spleen functions as a filter and site for phagocytic clearance of the bloodstream, removing degenerate and aged red blood cells as well as particulate materials and circulating bacteria 3, 4
- It serves as a primary site of extramedullary hematopoiesis 4
- The spleen is essential for mounting early IgM immune responses 3
- It combines innate and adaptive immune systems in a uniquely organized way 2
Anatomical Organization
- The spleen consists of two main compartments: white pulp (including the marginal zone) and red pulp, which differ significantly in architecture, vascular organization, and cellular composition 1
- This unique architecture allows for interactions between the circulatory, reticuloendothelial, and immune systems 5
- The structure enables efficient removal of blood-borne microorganisms and cellular debris 2
Clinical Significance
- The spleen is vulnerable to trauma and may require surgical intervention in cases of severe injury 6
- After splenectomy, patients are at increased risk for overwhelming post-splenectomy infection (OPSI), particularly from encapsulated bacteria such as Streptococcus pneumoniae 6
- Vaccination against encapsulated bacteria is recommended for patients who undergo splenectomy 6
- The spleen can be the site of both antibody production and circulating cell destruction in autoimmune diseases 5
Pathological Considerations
- Splenic lesions may affect the red pulp, white pulp, or both compartments 4
- The spleen can be a site of direct and indirect toxicity, a target for some carcinogens, and a site for metastatic neoplasia 4
- Splenic infarction typically appears as peripheral low-density, wedge-shaped areas on CT imaging 7
The spleen's critical role in immune function and blood filtration makes it an essential organ for antibacterial and antifungal immune reactivity 2.