Spleen: Definition, Structure, and Function

Spleen Definition

The spleen is a small organ, typically located on the left side of the body, behind the ribcage and stomach. It is the largest organ in the body’s lymphatic system, which is responsible for promoting immune function, filtering the blood, and managing blood volume.

The lymphatic system is the system of ducts and lymph nodes which are found under the skin. They are a channel through which white blood cells can travel outside of the blood stream, and they are also a receptacle for bacteria, dead cells, debris, and extra fluid that may accumulate in the blood.

The spleen performs several helpful functions for the body, including making antibodies, removing bacteria, removing old red blood cells, breaking down waste products of red blood cells, recycling iron for use in new red blood cells, and holding a reserve of red blood cells and immune cells which the body can use in case of emergencies.

The spleen makes antibodies in a type of tissue called “white pulp.” Its tissue called “red pulp” contains a reservoir of immune cells that fight infection and promote tissue healing, which the spleen can release as needed.

The image below shows where the spleen is located in the body, along with the arrangement of its “red pulp” and “white pulp”:


Though the spleen is useful to the body, it is not essential for survival. Some of its functions can be taken over by other organs if the spleen is removed; other functions of the spleen are helpful in case of emergency, but are not required for survival under most circumstances.

The spleen may need to be removed if it becomes injured or infected. In these cases the spleen may pose more of a risk than a benefit to the rest of the body, and doctors may elect to perform surgery to remove it.

The spleen can also be damaged by sickle cell disease, which can block blood flow to the spleen. This is one reason why people with sickle cell disease should get extra immunizations.

People without a spleen typically lead normal, healthy lives, though they are advised to take regular immunizations to protect against infection.

Interestingly, about 10% of people have an “accessory spleen” – a small extra spleen! This causes no problems or symptoms, and most people only find out they have an accessory spleen if they require imaging scans of their body for another reason.

Spleen Function

The spleen performs numerous helpful functions for the body, including:

  • Making antibodies
  • Storing emergency reserves of red blood cells that can be released in case of blood loss
  • Storing emergency reserves of white blood cells that can be released to fight infection and promote healing
  • Breaking down waste products from dead cells
  • Recycling useful components, such as iron, for use in future red blood cells

It’s easy to see how the spleen helps us to survive illness and injury, and helps us to salvage useful nutrients.

In the modern era, spleens are not necessary for survival. With thorough safeguards such as vaccinations and antibiotics and the ability to take iron supplements if necessary, people without spleens are simply advised to be a little more careful about getting vaccinated and avoiding disease.

The spleen is most commonly removed because of injury, such as injuries sustained during car crashes or playing sports. An injured or ruptured spleen cause massive blood loss which can quickly become life-threatening.

There is some research suggesting that the spleen might have a poorly-understood role in preventing cardiovascular disease, as one study found that people with their spleens removed were more likely to die of cardiovascular disease than a control group.

For this reason, some scientists advocate for better injury prevention, such as protective body armor for sports players, to reduce the possibility of spleen injuries that may result in the need for spleen removal.

Spleen Location

In most people, the spleen is located under the left side of the ribcage, next to the stomach. It normally cannot be felt or detected, as it is only about the size of the fist and is tucked away behind the stomach.

Its location makes the spleen fairly well-protected, but it can still be injured by blows to the chest and side, such as those that are sometimes sustained in sports or in car accidents.

A ruptured spleen can be very dangerous to the rest of the body. This is because the spleen processes a large blood supply, so rupture of the spleen may lead to rapid, massive blood loss. For that reason, spleens are sometimes removed if they are injured and there is concern that they may rupture.

Doctors can sometimes feel the spleen if it is abnormally swollen, as in the case of mononucleosis, blood cancers, and other conditions. If someone is suspected of having those conditions, doctors may feel the abdomen for signs of an enlarged spleen.

Spleen Structure

The spleen consists of two different types of tissues, red pulp and white pulp. These tissues are encased within a membrane of tissue. The spleen’s external surface can be divided into two portions: the diaphragmatic surface, and the visceral surface. Here we’ll discuss more about each of these important features.

Diaphragmatic Surface

The diaphragmatic surface of the spleen is the surface which faces the diaphragm. This is an upward-facing surface that curves outward, pressing against the diaphragm.

The diaphragm – a strong muscle located beneath the lungs and stomach, which enables us to breathe – lies between the spleen and the lung.

Visceral Surface

The visceral surface of the spleen faces down, toward the organs of the “viscera,” “gut.” It is divided by a ridge into two regions: the renal region, and the gastric region.

The “gastric,” or stomach region is the “anterior,” or front surface of the spleen. It faces forward and curves inward, like a soup spoon. This allows it to curve around the stomach, which nestles into the spleen. The very bottom of the gastric region touches the tail of the pancreas.

The “renal,” or kidney region, faces in toward the center of the body and downward. It comes into contact with the front of the left kidney and sometimes with the left adrenal gland.

Red Pulp

The red pulp of the spleen serves the circulatory system by filtering the blood, and acting as a recycling station for red blood cells and a storage point for other important blood components. It makes up the majority of tissue in most healthy spleens.

The red pulp consists of connective tissue called the “cords of Billroth.” These first filter the blood, removing pathogens and red blood cells that have reached the end of their useful lives. It then uses immune cells called macrophages to break down the useless or harmful components of these cells, while saving useful components such as iron for use in future red blood cells.

The red pulp also stores white corpuscles (another type of white blood cell), special cells called “splenic cells” which store, digest, and transport red blood cells, and platelets.

On occasion, platelet deficiency may occur of the spleen stores too many platelets and does not release enough of them into the blood.

White Pulp

The white pulp of the spleen is the tissue that performs the spleen’s immune functions. It consists of a layering of different tissues and nodules, each of which perform distinct functions for the immune system:

  • The periarteriolar lymphoid sheaths (PALS) serve as a reservoir for white blood cells called T lymphocytes. Some scientists have described this reserve of white blood cells as being similar to having a standing army, ready to mobilize to protect the body in the event of attack.
  • The lymph follicles contain a type of blood cell called B lymphocytes, which divide and reproduce inside the follicles. Antibody molecules that help the immune system to recognize and fight illness are also made in this tissue.Other tissues in the body also perform these functions, so they will not cease if the spleen is removed; but the spleen lends the immune system extra strength by producing these cells and antibodies.
  • The marginal zone contains a unique type of cell called “antigen presenting cells.” Antigens are molecules found on bacteria or viruses which antibodies and white blood cells recognize. The term literally comes from “anti-” for “antibody” and “gen” for “beginning.”

Antigen-presenting cells serve the immune system by eating invading pathogens, and then presenting molecules from the pathogens on the surface of their cells. This can “teach” and stimulate other immune cells to respond to new pathogens.

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