**2. Physiologyof the spleen**

The spleen is a major hematopoietic organ containing approximately 25 percent of the total lymphoid mass of the body; and it is capable of supporting elements of the erythroid, myeloid, megakaryocytic, lymphoid, monocytic, and macrophagic (reticuloendothelial) systems. As such, it is important in the following situations:

### **2.1. Phagocytosis**

138 Aneurysm

**Figure 3.**

**1.5. Venous drainage** 

**1.6. Lymphatic drainage** 

**1.7. Nerve supply** 

**1.8. Surface marking** 

omental, pancreatic, and inferior mesenteric veins.

trabeculae and drain to the pancreaticosplenic lymph nodes.

Sympathetic fibers are derived from the celiac plexus.[2, 3, 4]

The principal venous drainage of the spleen is through the splenic vein. It is formed at the hilum and runs behind the pancreas then joins the superior mesenteric vein behind the neck of the pancreas to form the portal vein. Its tributaries are the short gastric, left gastro-

Splenic tissue proper has no lymphatics. However, a few arise from the capsule and

The spleen is marked on the left side of the back with the long axis of the 10th rib. The upper border is marked along the upper border of the 9th rib; the lower border, along the 11th rib. The medial end lies 5 cm from the midline, and the lateral extension is to the midaxillary line.[5]

Phagocytosis is one of the most important functions of the spleen. The spleen forms a component of the reticuloendothelial system. The splenic phagocytes include reticular cells, free macrophages of the red pulp, and modified reticular cells of the ellipsoids. The phagocytes present in the organ remove debris, old and effete red blood cells (RBCs), other blood cells, and microorganisms; thus, the splenic phagocytes filter the blood. Phagocytosis of circulating antigens initiates the humoral and cellular immune responses.

This function is most apparent when the spleen has been removed, since splenectomized patients are susceptible to bacterial sepsis, especially with encapsulated organisms.

#### **2.2. Hematopoiesis**

The spleen is an important hematopoietic organ during fetal life; lymphopoiesis continues throughout life. The manufactured lymphocytes take part in immune responses of the body. In the adult spleen, hematopoiesis can restart in certain diseases such as chronic myeloid leukemia and myelosclerosis.

#### **2.3. Active immune responses**

Following antigenic stimulation, increased lymphopoiesis for cellular responses and increased formation of plasma cells for humoral responses occurs.
