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Discover the fascinating functions and mysteries of the spleen, the lesser-known organ that plays a crucial role in our immune system and overall health.

USMLE Guide: Spleen


The spleen is an important organ located in the upper left side of the abdomen. It plays a crucial role in the immune system, hematopoiesis, and filtration of the blood. Understanding the anatomy, function, and associated disorders of the spleen is essential for medical professionals preparing for the USMLE exams.


  • Location: The spleen is located in the left upper quadrant of the abdomen, beneath the diaphragm and behind the stomach.
  • Size and Shape: It is approximately 12 cm long and weighs around 150 grams. The spleen has a bean-like shape.
  • Structural Components: The spleen is composed of red pulp, white pulp, and a connective tissue capsule.
    • Red Pulp: This region contains sinuses filled with red blood cells, as well as macrophages responsible for filtering old or damaged blood cells.
    • White Pulp: This area is involved in immune responses, containing lymphocytes and other immune cells.
    • Connective Tissue Capsule: It surrounds the spleen and sends trabeculae into the organ, providing structural support.


  1. Immune System: The spleen is an integral part of the immune system, acting as a secondary lymphoid organ. It filters blood and helps in the production of antibodies, promoting the destruction of pathogens and foreign substances.
  2. Hematopoiesis: During fetal development, the spleen contributes to the production of red blood cells. In adults, it serves as a hematopoietic organ in case of emergency situations or certain diseases.
  3. Blood Filtration: The spleen filters the blood, removing old or damaged red blood cells, platelets, and other foreign particles. Macrophages located in the spleen play a vital role in this process.

Clinical Conditions

  1. Splenomegaly: Enlargement of the spleen, often caused by infections (e.g., mononucleosis), liver cirrhosis, or blood disorders (e.g., leukemia). Symptoms include pain, early satiety, and anemia.
  2. Splenic Rupture: Usually caused by trauma to the abdomen, resulting in severe abdominal pain, hypotension, and signs of internal bleeding. Immediate medical attention is crucial.
  3. Hypersplenism: Associated with excessive destruction of blood cells within the spleen, leading to anemia, thrombocytopenia, and leukopenia. It can occur in various conditions, including liver diseases, autoimmune disorders, or infections.
  4. Splenic Infarction: Blockage of the splenic artery or its branches, typically due to embolism or thrombosis. Symptoms include sudden left upper abdominal pain and fever.
  5. Hematological Disorders: Some blood disorders, such as hereditary spherocytosis, may directly affect the spleen due to abnormal red blood cells, leading to chronic hemolysis and an increased risk of splenic complications.

Diagnostic Techniques

  • Physical Examination: Palpation of the abdomen may reveal an enlarged spleen (splenomegaly).
  • Ultrasound: A non-invasive imaging technique commonly used to diagnose spleen abnormalities.
  • Computed Tomography (CT): Provides detailed images of the spleen and surrounding structures, helpful in diagnosing trauma, tumors, or other splenic conditions.
  • Magnetic Resonance Imaging (MRI): Can provide additional information regarding spleen structure and blood flow.
  • Laboratory Tests: Blood tests, such as a complete blood count (CBC), can help assess the function of the spleen and detect any associated abnormalities.

Remember to refer to comprehensive textbooks and resources for a more in-depth understanding of spleen-related topics. Good luck with your USMLE preparations!

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