The spleen is the largest organ of your lymphatic system which consists of network of trabeculae, blood vessels and lymphoid tissue.
It resides in the upper left of the abdomen and is protected by the rib cage. The region is also known as left hypochondriac region.
It provides a milieu where lymphocytes proliferate and old damaged red blood cells are recycled and filter the blood for detecting microorganism presence.
Apart from this, it acts as a large reservoir of blood which is deployable in emergency situations.
Anatomy of Spleen
Location and structure
The normal spleen is a bean-shaped structure and resides in the upper left of the abdomen posterior to the stomach and anterior to the left hemidiaphragm at the levels of 9-10 ribs. The left kidney is on the medial side and superiorly diaphragm is present. Inferiorly it rests directly on the left colic flexure or splenic flexure of colon.
All the surfaces are covered with peritoneum, making it an intraperitoneal organ. Only the hilum is devoid of the peritoneal cover.
The spleen is normally not palpable, being palpable only when enlarged significantly.
The normal size of the is roughly equal to size of the fist and color is purple.
Normal size is 7cms to 14 cms in length. It usually weighs between 150- 200 grams.
Ultrasonic measurements have revealed dimensions to be [may vary with the population studied]
- Length 7.7-13.7 cms
- Width 2.94 – 7.02 cms
- Depth 5.8-12.4 cms
An easy way to remember the anatomy of the spleen is the 1×3×5×7×9×11 rule.
Dimensions – 1x3x5 inches (3x8x13 cm),
Weight – 7Oz (200gm)
Location – Leis between 9-11th ribs
Borders and Surfaces
Image Credit: Stat Pearls
The spleen has three borders superior, inferior, and anterior. The superior border limits the gastric area, the inferior border bounds the renal area and the anterior border limits the colic area.
There are two small extensions of splenic mass which are called anterior and posterior extremities. The spleen has a smooth, convex surface that faces the diaphragm called diaphragmatic surface.
The other side, the visceral surface is divided by a ridge into anterior gastric and posterior renal part.
The gastric surface is directed forward, upward, and toward the middle.
It is broad, concave, and is in relation to the posterior wall of the stomach above and pancreas below.
The renal surface is narrower and is directed medialward and downward. It is related to the upper part of the anterior surface of the left kidney.
The splenic hilum is found in the central part of the visceral surface.
It is surrounded by a fibroelastic capsule which allows it to significantly increase its size when necessary.
Splenic Ligaments
Image Credit: Basic Medical Key
Gastrosplenic ligament
It connects the hilum with the greater curvature of the stomach. It contains the short gastric vessels and left gastroomental (gastroepiploic) arteries and veins.
Splenorenal ligaments
It connects the hilum with the left kidney. It transmits the splenic artery and vein.
Phrenicolic Ligament
Lastly, the spleen sits on the phrenicocolic ligament which originates from the colon and is also known as the sustentaculum lienis.
Pancreaticosplenic ligament, pancreatocolic ligament, splenocolic ligament and presplenic fold are other minor ligaments
Blood Supply
The splenic artery, a branch of celiac trunk, is the source of blood supply reaches the spleen traveling through the splenorenal ligament. Celiac trunk is a branch of the abdominal aorta.
Splenic vein drains the blood from spleen. It also receives blood from the inferior mesenteric vein. It unites with the superior mesenteric vein, behind the neck of pancreas to form the hepatic portal vein.
Lymphatic drainage
The splenic lymph nodes are present at the hilum and receive lymph via perivascular and subcapsular lymphatic vessels. It is then drained to the superior pancreatic lymph nodes at the superior surface of the pancreas.
Then the lymph moves to the celiac lymph nodes.
Microscopic Anatomy
Understanding the microscopic arrangement helps to understand the function of the spleen.
Capsule sends numerous septa called trabeculae from the capsule into the parenchyma of the spleen.
These trabeculae [and capsule too] contains myoepithelial cells which provide them contractile ability.
This ability is used to pump out the stored blood when body needs it as in case of bleeding or physiological demand as in exercise.
The parenchyma of the spleen is called pulp.
There are two kinds of pulp based on their color on histological sections – white and red.
White pulp is responsible for reactive immune response. It is the main lymphoid tissue of the spleen.
It is composed of nodules, called Malpighian corpuscles. Malphigian corpuscle is composed of lymphoid follicles rich in B-lymphocytes and periarteriolar [around an arterial vessel, branch of splenic art] lymphoid sheath, rich in T-lymphocytes.
Red pulp is responsible for the filtration of red blood cells. It is a marginal zone bordering on white pulp and is formed by venous sinuses or sinusoids which are filled with blood and splenic cords of reticular fibers. These reticular cords are also called cords of Billroth.
Image Credit: ScienceDirect
There is the lining of splenic macrophages around the cords.
The central artery of the PALS continues from the white pulp and enters the red pulp as a capillary. These capillaries empty into the splenic cords.
Macrophages present here phagocyte old and damaged erythrocytes.
The blood then diffuses into the splenic sinuses, thus returning to the venous circulation.
Functions of the Spleen
- Immune responses on antigenic stimulation
- Increased formation of plasma cells for humoral responses
- Increased lymphopoiesis for cellular responses occurs.
- Phagocytosis
- Carried by the reticular cells and free macrophages
- Removes debris, old and ineffective RBCs, other blood cells, and microorganisms
- Phagocytosis of circulating antigens begins immune response
- Hematopoiesis
- Produces all types of blood cells during fetal life
- Lymphopoiesis occurs throughout life
- Blood Storage
- About 8% of the circulating RBCs are present within it
- Can be used in increased physiological or pathological demands
Anatomical Variations
- Accessory spleens
-
- Also called splenunculi
- Formed from nodules that fail to fuse during development
- Sites
- Gastrosplenic ligament
- Splenorenal ligament
- Gastrophrenic ligament
- Gastrocolic ligament
Clinical Significance and Conditions affecting Spleen
Trauma
Trauma may lead to a ruptured spleen. It can cause life-threatening internal bleeding. Swollen spleens can rupture even with lesser trauma.
Splenomegaly
Enlargement of the spleen is known as splenomegaly.
It can result from various causes such as infection, blood flow obstruction, anemia or infiltration diseases.
[Read more about splenomegaly]
Asplenia
It means absence or non-functional spleen. It could be congenital, traumatic or in diseases like sickle cell anemia.
Asplenia refers to a non-functioning spleen, which may be congenital, or caused by traumatic injury, surgical resection (splenectomy) or a disease such as sickle cell anemia.
Hyposplenia refers to a partially functioning one.
Absence nonfunctioning spleen could lead to increased susceptibility to the infections.
Polysplenia
A congenital disease where multiple small accessory spleens are present instead of one full-sized, normal spleen. It is often accompanied by other abnormalities such as intestinal malrotation, biliary atresia, or cardiac abnormalities.
The accessory spleens are non-functional.
Splenic infarction
It occurs when the splenic artery or its branches are occluded, for example by a blood clot.
The typical symptom is that of severe pain in left upper quadrant and may radiate to shoulder as well. It may be accompanied by fever and chills.
Hyaloserositis
In this disorder, the spleen is coated with fibrous hyaline.