This section describes the spleen and its structures.

Figure 1. & Figure 2.

Spleen Anatomy

The spleen, an organ of mystery and perplexity since ancient times, is located in the left upper abdominal cavity (Fig. 1). It weighs about 150 grams and is approximately 12cm long, 7cm wide, and 3-4cm thick. The spleen is located between the fundus of the stomach and the diaphragm, while also being in contact with the left kidney posteriorly. The gastric surface is concave and located at the level of the eleventh thoracic vertebra. The lower extremity of the spleen lies against the flexure of the colon (Fig. 2 & Fig. 3 ). It is held in position by three folds in the peritoneum which are: phrenicolienal ligament, gastrolienal ligament, phrenicocolic ligament. The spleen is divided into compartments by connective tissue (trabeculae). The compartments contain white pulp, red pulp, and venous sinuses 2,3 .

Figure 3

Figure 4.

Spleen Blood Supply

Arterial blood is delivered (about 300mL/min 4 ) to the spleen via the descending aorta and the splenic artery. Within the spleen, the lineal artery divides into six or more branches that become increasingly smaller and more branched bringing the blood into contact with the splenic pulp and venous sinuses. Blood departs via the splenic vein- the inferior mesenteric vein- the superior mesenteric vein, and finally the portal vein (Fig. 4 ).

Spleen Innervation

Nervous innervation is delivered from the celiac plexus and is distributed along the blood vessels and smooth muscle of the spleen.

Spleen Lymphatics

The lymphatics of the spleen primarily flow to the pancreaticolineal glands, which follow the splenic artery. These glands then join the preaortic glands.

Figure 5.

Spleen Function

The spleen is a secondary lymphoid organ. The splenic white pulp is primarily lymphoid tissue and is the primary site of immune and phagocytic action. Here, the spleen processes foreign antigen and produces specific immunoglobulin M. The red pulp is the primary site of splenic filtration. Within the red pulp, macrophages destroy old or bad RBC's, microorganisms, and remove particles of debris (Fig. 4 ). The macrophages also sometimes repair damaged RBC's and return them to the circulation. The venous sinuses are distensible areas capable of storing more than 300mL of blood with the help of the red pulp (Fig. 5). During times of low blood pressure, sympathetic stimulation can cause the spleen to contract and return about 200mL of blood back into circulation. The spleen is not necessary for life, but if the spleen is removed, decreases in immune function, decreases in circulating iron, and increased numbers of defective RBC's may be observed.

Basic Study Questions

  1.  List three functions of the spleen.

  2.  What is the difference between functions of white pulp and red pulp?

  3.  Splenic innervation is through which plexus?

Additional Study Questions