Spleen

Introduction

Introduction to the Spleen

The spleen is the largest secondary lymphoid organ, situated in the left upper quadrant of the abdomen, protected by the 9th–11th ribs. It lies posterior to the stomach and lateral to the left kidney, suspended by the gastrosplenic and splenorenal ligaments. Functionally, it filters blood, mounts immune responses, and stores platelets and red blood cells.

Embryologic Origin

The spleen develops from mesenchymal cells within the dorsal mesogastrium, a derivative of the foregut mesentery, during the fifth week of gestation. Unlike true foregut organs, it does not arise from endoderm but shares vascular connections with foregut structures, explaining its anatomical relationships.

Study

Anatomical Position and Relations

The spleen occupies the left hypochondriac region, extending from the level of the 9th rib to the 11th rib. It is in close contact with the fundus of the stomach medially, the diaphragm superiorly, and the left colic flexure inferiorly. Its peritoneal attachments—gastrosplenic and splenorenal ligaments—contain the splenic vessels and provide limited mobility.

Capsule and Trabeculae

A fibroelastic capsule encloses the spleen, extending inward as trabeculae that partition the organ into lobules. These trabeculae support the splenic parenchyma and guide the course of the splenic artery, vein, and nerves. The capsule also serves as a barrier to infection, limiting spread of pathogens.

White Pulp and Red Pulp

The spleen is divided into white pulp (lymphoid tissue) and red pulp (vascular tissue). White pulp consists of periarteriolar lymphoid sheaths (PALS) surrounding central arterioles and lymphoid follicles that initiate adaptive immune responses. Red pulp contains splenic cords and sinusoids that filter aged erythrocytes and platelets, and it serves as a reservoir for blood components.

Vascular Supply and Drainage

The splenic artery, a branch of the celiac trunk, reaches the spleen via the splenorenal ligament and branches into trabecular arteries. Venous blood drains through the splenic vein, which joins the superior mesenteric vein to form the portal vein. This unique portal circulation links splenic filtration directly to hepatic processing.

Clinical Significance

Trauma to the left upper abdomen can cause splenic rupture, leading to intra‑abdominal hemorrhage—a surgical emergency. Hypersplenism results in cytopenias due to excessive sequestration of blood cells. Splenectomy, indicated for certain hematologic disorders, predisposes patients to encapsulated bacterial infections, necessitating vaccination.

Summary

Key Takeaways

The spleen resides in the left upper abdomen, is encapsulated, and is divided into white and red pulp with distinct immunologic and filtration roles. It receives arterial blood from the celiac trunk and drains into the portal system, linking it to hepatic function. Clinically, splenic injury, hypersplenism, and post‑splenectomy infection risk are paramount considerations.

Clinical Correlate

Understanding splenic anatomy guides the management of blunt abdominal trauma, informs decisions about splenectomy versus splenic preservation, and underscores the need for prophylactic vaccinations against encapsulated organisms in asplenic patients.