The spleen’s main functions are to filter the blood and help defend the body against pathogens. In this article, we will explain its anatomy, what it does, and what happens when it goes wrong.

The spleen has long been a source of interest and mystery. The Ancient Greeks thought it existed to keep the liver clean. In medieval times, people saw it as the source of “black bile” and melancholy, while writings from the 1600s refer to it as a source of joviality.

Some considered it useless and believed it was best removed if diseased. It was only in the 20th century that doctors started to understand what the spleen really does.

The spleen plays a key role in the body’s immune response, which involves defending the body against pathogens, and in the hematological system, which relates to the various components of blood.

The spleen is located behind ribs 9 through 11 in the upper left of the abdomen, protected by the rib cage. It is the largest organ of the lymphatic system — the circulatory component of the immune system. It recycles iron, destroys old red blood cells, and stores white blood cells and platelets, the components of the blood that help stop bleeding.

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Explore the 3D model using your mouse pad or touchscreen to understand more about the spleen.

The weight of the spleen varies among individuals, ranging from around 70–200 grams (g). It is usually around 12 centimeters (cm) long, 7 cm across, and 5 cm thick.

Anything that relates to the spleen is referred to as “splenic.” The spleen receives blood through the splenic artery, and blood leaves the spleen through the splenic vein. The spleen is connected to the blood vessels of the stomach and pancreas, but it does not play a role in digestion.

The spleen contains two main regions of tissue called white pulp and red pulp.

Red pulp

Red pulp contains venous sinuses (cavities filled with blood) and splenic cords (connective tissues containing red blood cells and white blood cells).

Red pulp:

  • filters the blood
  • removes old, damaged, or unwanted red blood cells
  • contains white blood cells that destroy viruses, bacteria, fungi, and other pathogens
  • stores white blood cells and platelets for release when the body needs them for healing, managing inflammation, and boosting blood supply in the case of an injury

White pulp

White pulp produces white blood cells, particularly types B and T lymphocytes and antibodies. The cells mature in the white pulp.

Between the red and white pulp is the marginal zone, a border that filters pathogens out of the blood and into the white pulp.

The spleen’s main roles are:

  • filtering old or unwanted cells from the blood
  • storing red blood cells and platelets
  • metabolizing and recycling iron
  • preventing infection

The spleen filters the blood, removing old or unwanted cells and platelets. As blood flows into the spleen, it detects any red blood cells that are old or damaged. Blood flows through a maze of passages in the spleen. Healthy cells flow straight through, but those considered unhealthy are broken down by large white blood cells called macrophages.

After breaking down the red blood cells, the spleen stores useful leftover products, such as iron. Eventually, it returns them to the bone marrow to make hemoglobin, the iron-containing part of blood.

The spleen also stores blood cells that the body can use in an emergency, such as severe blood loss. The spleen holds around 25–30% of the body’s red blood cells and about 25% of its platelets.

The spleen’s immune function involves detecting pathogens, such as bacteria, and producing white blood cells and antibodies in response to threats.

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1683469-What Does the Spleen Do.Illustration by Antonio Jimenez 1683469-What Does the Spleen Do Medical Illustration, Abdomen, Medical Illustration, Stomach, intestine, liver, spleen Medical illustration by Antonio Jimenez

Some health conditions can involve the spleen. They include the following.

Accessory spleen

An estimated 10–30% of people have an additional spleen, called an accessory spleen. The second spleen is usually much smaller — around 1 cm long — but can be larger. They work in a similar way to a spleen but do not have all the same features.

An accessory spleen does not usually cause health problems. In rare cases, however, a large accessory spleen can become twisted, leading to pain, nausea, and possibly internal bleeding. In this case, a person will need surgery.

Ruptured spleen

This can occur following an injury or with certain health conditions. It can cause life threatening internal bleeding.

The spleen may burst at the time of the injury or up to several weeks later.

Splenomegaly, or an enlarged spleen, can increase the risk of rupture as the capsule containing the spleen becomes thinner.

Enlarged spleen (splenomegaly)

This can happen when the spleen becomes overactive, such as when responding to an infection. It can also indicate congestion due to a blockage or growth, such as a tumor.

Conditions that can lead to an enlarged spleen include:

  • portal hypertension, which can cause too much blood to accumulate in the splenic vein
  • a tumor or other accumulation of cells, for instance, with blood cancers (such as leukemia)
  • hypersplenism, or an overactive spleen, due to an increase in immune activity; possible causes include an infection or autoimmune disease
  • cancer that affects immune cells, as with lymphoma
  • liver disease

If a person can feel their spleen more than 2 cm below their rib cage, this may be a sign of splenomegaly. Other symptoms include:

  • pain in the upper left abdomen, which may reach to the left shoulder
  • abdominal bloating or swelling
  • low appetite or feeling full after eating little

There may also be other symptoms due to the underlying cause, such as a fever stemming from an infection.

If the spleen weighs 400–500 g and is 12–20 cm long, a doctor will diagnose splenomegaly. Massive splenomegaly is when the spleen weighs over 1,000 g and measures over 20 cm in length.

Sickle cell disease

This is an inherited form of anemia in which the red blood cells have an unusual crescent shape. This shape interferes with normal blood circulation and shortens red blood cell lifespan, leading to low levels of hemoglobin throughout the body.

Sickle cell disease can cause damage to all organs, including the spleen. It may prevent the spleen from working properly. This can affect the immune response, leaving the person more susceptible to infections.

Preventive treatment can help prevent spleen problems due to sickle cell disease. In some cases, surgery may be necessary to remove the spleen.

Extravascular hemolysis

This is when red blood cells break down in the spleen or liver. It can lead to high levels of bilirubin, a yellow pigment. The liver usually breaks down bilirubin, but extravascular hemolysis can result in unusually high levels in the blood.

Extravascular hemolysis can lead to:

Causes include sickle cell disease and malaria.

Some people need surgery to remove their spleen, known as a splenectomy.

Possible reasons include:

  • a ruptured spleen
  • an enlarged spleen
  • certain blood disorders
  • some cancers and noncancerous growths

It is possible to live without the spleen, as other tissues, such as the lymph nodes and liver, can take over many of its tasks.

However, people who have had their spleen removed are more susceptible to infections. The risk may be higher for those with celiac disease, sickle cell disease, or conditions that affect the immune system, such as HIV.

Here are some answers to questions people often ask about the spleen.

What does the spleen do?

The spleen supports the immune system and blood production and maintenance.

What are the signs of a problem with the spleen?

Abdominal pain, swelling, and jaundice may be signs of an enlarged spleen. There is often an underlying cause that needs addressing.

What diseases affect the spleen?

Cancer, sickle cell disease, malaria, portal hypertension, infections, and diseases that affect the immune response can all give rise to spleen problems.

The spleen is located just behind the lower ribs.

It plays a key role in removing old and unwanted blood cells and in the immune response. Various conditions can affect the spleen, and sometimes an individual needs surgery to remove it.

A person can live without a spleen, but they will have a higher risk of infection and will need to take measures to protect themselves, such as vaccination.