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The spleen is the largest organ of your lymphatic system, a subdivision of the immune system. Its network of trabeculae, blood vessels and lymphoid tissue provides an environment in which white blood cells (lymphocytes) proliferate while old damaged red blood cells (erythrocytes) are recycled.
Although it may seem dispensable as it is possible to live without it, the spleen is constantly filtering the blood in order to detect the presence of microorganisms. If you find yourself in the emergency room, the spleen also holds a large reservoir of blood which can be pumped back into circulation if needed.
| Definition | An intraperitoneal lymphoid organ found on the left side of the abdomen inferior to the diaphragm. |
| Location | Left hypochondriac region (left upper quadrant) |
| Structure | Capsule, trabeculae, white pulp, red pulp |
| Function | Immune surveillance, proliferation and maturation of lymphocytes, degradation of senescent and damaged erythrocytes |
| Neurovascular supply | Artery: splenic artery Vein: splenic vein Lymph: celiac node Innervation: celiac plexus |
| Clinical relations | Splenectomy |
This page will describe the anatomy of the spleen and its functions.
To best depict the location of the spleen, we’ll describe its relations. The spleen is found in the left hypochondriac region of the abdomen (left upper quadrant). More precisely, the spleen is located posterior to the stomach and anterior to the left hemidiaphragm at the level of ribs 9-10. Medial to the spleen is the left kidney; superior is the diaphragm, while inferiorly it rests directly on the left colic flexure (splenic flexure).
Although the spleen can descend as far as the pubic symphysis, as seen in mantle cell lymphoma, it normally does not move beyond the left rib arch and so is unavailable for palpation in healthy individuals.
The spleen is a purple, fist-sized organ. It is wrapped by a fibroelastic capsule which allows the spleen to significantly increase its size when necessary. The spleen is an intraperitoneal organ, so all of its surfaces are covered with visceral peritoneum. Only the hilum of the spleen, the site through which the splenic artery and vein pass, is peritoneum-free.
Organs near to the spleen leave their impressions on its surfaces which, together with spleen borders, can easily be observed and described.
The spleen has three borders (superior, inferior, and anterior) as well as two extremities (anterior and posterior). The superior border bounds the gastric area, the inferior border bounds the renal area and the anterior border bounds the colic area.
Three ligaments originating from the surrounding structures attach to the spleen. Two of these ligaments connect to the splenic hilum and are traversed by the transmitted splenic vessels. The gastrosplenic ligament connects the hilum with the greater curvature of the stomach. It contains the short gastric vessels and left gastroomental (gastroepiploic) arteries and veins. The splenorenal ligament connects the hilum of the spleen with the left kidney. It transmits the splenic artery and vein. Lastly, the spleen sits on the phrenicocolic ligament which originates from the colon and is also known as the sustentaculum lienis.
For more details about the anatomy of the spleen, jump directly into our integrated quiz on the structure of the spleen:
Understanding the microscopic anatomy of the spleen is important for understanding its function. Numerous septa called trabeculae extend from the dense irregular fibroelastic connective tissue of the capsule into the parenchyma of the spleen. Both the capsule and trabeculae contain myoepithelial cells which have the ability to contract. As the spleen stores a significant amount of blood, the contraction of myoepithelial cells pumps stored blood into the circulatory system when the body is in need; for example during intense physical activity or massive hemorrhage.
The parenchyma of the spleen is called pulp. Based on the color of the pulp on fresh sections, white and red pulp can be distinguished. White pulp is the main lymphoid tissue of the spleen. It is the accumulation of lymphocytes around an arterial vessel. This aggregation of lymphocytes constitutes the lymphoid tissue known as periarterial lymphoidsheath (PALS) and it is the first to react if microbes reach the spleen through the bloodstream. The central arterial vessels in PALS nodules are branches of the splenic artery.Red pulp consists of splenic venous sinuses and cords (of Billroth), linings of splenic macrophages around the sinuses. The central artery of PALS continues from the white pulp and enters the red pulp as a capillary. These capillaries empty into the splenic cords, where macrophages phagocyte old and damaged erythrocytes. From there, blood diffuses into the splenic sinuses, thus returning to the venous circulation.
You can quiz your knowledge on the histological aspects of the spleen with our quiz in multiple difficulty levels:
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