- Related Topics:
- lymphoid tissue
- red pulp
- splenic lymph follicle
- white pulp
- On the Web:
- National Center for Biotechnology Information - Physiology, Spleen (Nov. 01, 2026)
spleen
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What is the spleen?
The spleen is an organ of the lymphatic system, found on the left side of the abdominal cavity under the diaphragm. It is about the size of a fist and is well supplied with blood. The spleen is the primary filtering element for the blood. It also stores and releases immune cells that mediate tissue inflammation.
The spleen has two types of tissue: red pulp and white pulp. The white pulp contains lymphoid elements and reacts to microorganisms and antigens by releasing macrophages. The red pulp filters blood and destroys old red blood cells, breaking down hemoglobin for excretion and iron recycling.
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Where is the spleen located in the human body?
The spleen is in the upper-left side of the abdominal cavity, beneath the diaphragm which separates the abdomen and chest. It is about the size of a fist and is well supplied with blood. The spleen is an important part of the lymphatic system, filtering blood and storing immune cells that help mediate tissue inflammation.
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What does the spleen look like?
The spleen, found on the left side of the abdominal cavity under the diaphragm, resembles the size of a fist and has a rich blood supply. A thick connective-tissue capsule encases it.
Inside, the splenic tissue consists of red pulp and white pulp that intermingle. The white pulp is lymphoid tissue surrounding blood vessels, while the red pulp is a network of splenic cords and sinusoids filled with blood where filtration occurs.
The white pulp contains lymphoid elements like plasma cells and lymphocytes, and the red pulp acts as a reservoir for macrophages and monocytes.
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What are the main functions of the spleen?
The spleen, found in the upper left abdomen, is a fist-sized lymphatic system organ that filters blood similarly to how lymph nodes filter lymphatic circulation.
Main functions:
* Filtering: It eliminates foreign materials and old or damaged red blood cells from the blood via macrophages, and it also triggers immune responses and antibody production.
* Immune Response: The spleen's white pulp, which contains lymphoid elements, produces lymphocytes and reacts to bloodborne antigens, initiating immune reactions.
* Monocyte Storage: The red pulp acts as a reservoir for monocytes, which aid in tissue repair and regulate inflammation. After injuries, the spleen releases monocytes to promote healing.
* Red Blood Cell Recycling: The spleen degrades old red blood cells, recycling iron for new hemoglobin.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does the spleen help the immune system?
The spleen, an organ of the lymphatic system, supports the immune system by filtering blood and storing immune cells. As blood passes through the spleen, macrophages eliminate bacteria, debris, and old blood cells. The spleen's white pulp contains lymphocytes that trigger antibody production, while the red pulp houses macrophages that remove foreign substances and initiate immune responses. The spleen also releases monocytes to regulate inflammation and facilitate tissue repair.
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What problems can happen if the spleen is injured or removed?
Injury to or removal of the spleen can lead to several problems. The spleen filters blood and releases immune cells that mediate tissue inflammation. If the spleen is injured, it may release monocytes, which help regulate inflammation and facilitate tissue healing. Removal of the spleen, called a splenectomy, may result in the monocyte response not being observed at the site of tissue injury, and healing is less thorough.
Additionally, people who have had their spleens removed appear to be at increased risk of infections, cardiovascular disease, and possibly certain types of cancer as they age. It is suspected that the absence of immune-regulating factors released from the spleen is related to the increase in susceptibility to such diseases in individuals who have undergone a splenectomy.
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spleen, organ of the lymphatic system located in the left side of the abdominal cavity under the diaphragm, the muscular partition between the abdomen and the chest. In humans it is about the size of a fist and is well supplied with blood. As the lymph nodes are filters for the lymphatic circulation, the spleen is the primary filtering element for the blood. The organ also plays an important role in storing and releasing certain types of immune cells that mediate tissue inflammation.
The spleen is encased in a thick connective-tissue capsule. Inside, the mass of splenic tissue is of two types, the red pulp and the white pulp, which do not separate into regions but intermingle and are distributed throughout the spleen. The white pulp is lymphoid tissue that usually surrounds splenic blood vessels. The red pulp is a network of splenic cords (cords of Billroth) and sinusoids (wide vessels) filled with blood, and it is in the red pulp that most of the filtration occurs.
The white pulp of the spleen contains typical lymphoid elements, such as plasma cells, lymphocytes, and lymphatic nodules, called follicles in the spleen. Germinal centres in the white pulp serve as the sites of lymphocyte production. Similar to the lymph nodes, the spleen reacts to microorganisms and other antigens that reach the bloodstream by releasing special phagocytic cells known as macrophages. Splenic macrophages reside in both red and white pulp, and they serve to remove foreign material from the blood and to initiate an immune reaction that results in the production of antibodies.
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The splenic cords in the red pulp in the spleen serve as important reservoirs for large quantities of macrophages and other phagocytic white blood cells called monocytes. Studies have shown that upon severe tissue injury, such as that sustained during a heart attack, the spleen releases a legion of monocytes, which then travel through the bloodstream to the site of injury. There they serve to regulate inflammation and to facilitate tissue healing. In animals who have had their spleens removed, the monocyte response is not observed at the site of tissue injury, and healing is less thorough. In addition, humans who have had their spleens removed (a procedure known as a splenectomy) appear to be at increased risk of infections and, as they age, cardiovascular disease and possibly even certain types of cancer. It is suspected that the absence of immune-regulating factors released from the spleen is related to the increase in susceptibility to such diseases in individuals who have undergone a splenectomy.
The red pulp has a specialized role in addition to filtration. It is the body’s major site of the destruction of red blood cells, which normally have a life span of only 120 days. Degenerate red cells are removed from the circulation in the spleen, and the hemoglobin that they contain is degraded to a readily excretable pigment and an iron molecule that is recycled (i.e., used to produce new hemoglobin elsewhere).
In some species the spleen also acts as a reservoir for blood during periods of inactivity. When such an animal is aroused for defense or flight, the capsule of the spleen contracts, forcing additional blood reserves into the circulation. It is unclear whether the human spleen has this capability.
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