Spleen
Illu spleen.jpg
The human spleen is located in the upper left abdomen, behind the stomach
Details
SystemImmune system (Lymphatic system)
ArterySplenic artery
VeinSplenic vein
NerveSplenic plexus
Identifiers
Latinsplen, lien
MeSHD013154
TAA13.2.01.001
FMA7196
Anatomical terminology
3D medical animation still showing structure of as well as location of the spleen in human body
A 3D medical animation still of spleen structure & exact location

The spleen is an organ found in virtually all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes from Ancient Greek σπλήν (splḗn).[1]

The spleen plays important roles in regard to red blood cells (erythrocytes) and the immune system.[2] It removes old red blood cells and holds a reserve of blood, which can be valuable in case of hemorrhagic shock, and also recycles iron. As a part of the mononuclear phagocyte system, it metabolizes hemoglobin removed from senescent red blood cells (erythrocytes). The globin portion of hemoglobin is degraded to its constitutive amino acids, and the heme portion is metabolized to bilirubin, which is removed in the liver.[3]

The spleen synthesizes antibodies in its white pulp and removes antibody-coated bacteria and antibody-coated blood cells by way of blood and lymph node circulation. These monocytes, upon moving to injured tissue (such as the heart after myocardial infarction), turn into dendritic cells and macrophages while promoting tissue healing.[4][5][6] The spleen is a center of activity of the mononuclear phagocyte system and is analogous to a large lymph node, as its absence causes a predisposition to certain infections.[7]

In humans the spleen is purple in color and is in the left upper quadrant of the abdomen.[3][8]

Anatomy

The spleen is underneath the left part of the diaphragm, and has a smooth, convex surface that faces the diaphragm. It is underneath the ninth, tenth, and eleventh ribs. The other side of the spleen is divided by a ridge into two regions: an anterior gastric portion, and a posterior renal portion. The gastric surface is directed forward, upward, and toward the middle, is broad and concave, and is in contact with the posterior wall of the stomach. Below this it is in contact with the tail of the pancreas. The renal surface is directed medialward and downward. It is somewhat flattened, considerably narrower than the gastric surface, and is in relation with the upper part of the anterior surface of the left kidney and occasionally with the left adrenal gland.

Measurements

90% confidence interval of maximum spleen length by abdominal ultrasonography by height of the person[9]
Height Spleen length
Women Men
155–159 cm 6.4–12 cm
160–164 cm 7.4–12.2 cm 8.9–11.3 cm
165–169 cm 7.5–11.9 cm 8.5–12.5 cm
170–174 cm 8.3–13.0 cm 8.6–13.1 cm
175–179 cm 8.1–12.3 cm 8.6–13.4 cm
180–184 cm 9.3–13.4 cm
185–189 cm 9.3–13.6 cm
190–194 cm 9.7–14.3 cm
195–199 cm 10.2–14.4 cm

The spleen, in healthy adult humans, is approximately 7 centimetres (2.8 in) to 14 centimetres (5.5 in) in length.

An easy way to remember the anatomy of the spleen is the 1×3×5×7×9×10×11 rule. The spleen is 1 by 3 by 5 inches (3 by 8 by 13 cm), weighs approximately 7 oz (200 g), and lies between the 9th and 11th ribs on the left-hand side and along the axis of 10th rib. The weight varies between 1 oz (28 g) and 8 oz (230 g) (standard reference range),[10] correlating mainly to height, body weight and degree of acute congestion but not to sex or age.[11]

Blood supply

Visceral surface of the spleen

Near the middle of the spleen is a long fissure, the hilum, which is the point of attachment for the gastrosplenic ligament and the point of insertion for the splenic artery and splenic vein. There are other openings present for lymphatic vessels and nerves.

Like the thymus, the spleen possesses only efferent lymphatic vessels. The spleen is part of the lymphatic system. Both the short gastric arteries and the splenic artery supply it with blood.[12]

The germinal centers are supplied by arterioles called penicilliary radicles.[13]

Nerve supply

The spleen is innervated by the splenic plexus, which connects a branch of the celiac ganglia to the vagus nerve.

The underlying central nervous processes coordinating the spleen's function seem to be embedded into the Hypothalamic-pituitary-adrenal-axis, and the brainstem, especially the subfornical organ.[14]

Development

The spleen is unique in respect to its development within the gut. While most of the gut organs are endodermally derived (with the exception of the neural-crest derived adrenal gland), the spleen is derived from mesenchymal tissue.[15] Specifically, the spleen forms within, and from, the dorsal mesentery. However, it still shares the same blood supply—the celiac trunk—as the foregut organs.

Function

Pulp

Micrograph of splenic tissue showing the red pulp (red), white pulp (blue) and a thickened inflamed capusule (mostly pink – top of image). H&E stain.
The spleen contains two different tissues, white pulp (A) and red pulp (B). The white pulp functions in producing and growing immune and blood cells. The red pulp functions in filtering blood of antigens, microorganisms, and defective or worn-out red blood cells.
Area Function Composition
red pulp Mechanical filtration of red blood cells. In mice: Reserve of monocytes[4]
white pulp Active immune response through humoral and cell-mediated pathways. Composed of nodules, called Malpighian corpuscles. These are composed of: