What Is Spleen in Human Body Definition, Structure, and 15+ Functions

What is Heart

Functions in Brief

A fist size organ, the spleen can swell up to hold 1 L of blood!

And beware! It’s no more the seat of emotions.

While WBCs make your military, the spleen is the ordnance factory.

Here’re key functions of spleen – the largest lymphatic organ.

This article also elaborates on the spleen functions in the succeeding sections.

Besides, you will learn about its conditions, discover interesting spleen facts, and get answers to FAQs about spleen like:

  • Where is the spleen located in the human body?
  • What is the spleen size and weight?
  • How does the function of spleen in human body cause anemia?
  • Is it a vital or non-vital organ?
  • Are people born without a spleen?
  • What happens when an individual is born with 2 spleens?
  • Is spleen a primary or secondary lymphoid organ?
  • Does the size of the spleen increase or decrease with age?
  • What happens when your spleen goes wrong?
  • How did the idiom “venting your spleen” come into use?

Suppose you call lymph nodes as the check posts that stop the infiltration of miscreants – foreign particles, toxins, wastes, and other unwanted materials – into the healthy body tissues.

What title would you suggest for the spleen? It might deserve the title of a major army base.

Read on to discover amazing facts about what is spleen in human body.

Spleen Definition:

The spleen can be defined as the largest gland of the lymphatic system, located to the left of the stomach, which helps your body combat diseases and get rid of debris.

The following spleen definitions will add to your understanding of the spleen location and function.

The OALD dictionary defines the organ as:

“A small organ in the vicinity of the stomach that controls the quality of blood cells.”

The Free Dictionary definition sheds more light on “What does the spleen do in the body?”

“The spleen is a large, highly vascular lymphoid organ located below the diaphragm and to the left of the stomach, which destroys old (or damaged) RBCs (Red Blood Cells), combats blood-borne antigens with its lymphocytes, and serves as a reservoir for blood.”

It means the spleen in body works in several capacities at the same time.

The organs lying close to the spleen include the gallbladder, the pancreas, the small intestine, the stomach, and the left kidney.

And the blood supply as viewed from below shows the structures like splenic veins, arteries, fibrous capsule, and splenic hilum.

Spleen Serving 3 Body Systems:

Your spleen works in 3 capacities. It makes a crucial part of 3 major systems of your body, i.e. the lymphatic system, the circulatory system, and the immune system.

The circulatory system has two main components, viz. the cardiovascular system and the lymphatic system.

Both the cardiovascular and lymphatic systems consist of networks of channels to transport fluids.

However, they have got different organs and involve different physiologies and dynamics to execute their jobs.

They also differ in the nature of end goals assigned to each.

While the main job of the cardiovascular system is to deliver oxygen and nutrients at the cell level, the lymphatic system fights the infection-causing germs and substances as its main task.

The immune system is your body’s defense system.

Involving different organs of the body, it struggles to counter germ attacks and prevent diseases.

Lymphatic System and Spleen:

Spleen is the largest organ of the lymphatic system.

However, it isn’t a major organ.

The major or the primary lymphoid organs are the bone marrow and the thymus.

It is because these organs play an active role in the synthesis of B- and T-cells.

Circulatory System and Spleen:

In the circulatory system, the spleen performs two important jobs.

First, it acts as a temporary reservoir for blood as one of its main jobs.

Second, it filters blood for germs and harmful or unwanted particles.

Immune System and Spleen:

In the immune system, the spleen has been recognized as the principal organ for the elimination of microorganisms that have not been opsonized, like an encapsulated bacterium.

Spleen Functions Elaborated:

“The Facts on File Illustrated Guide to the Human Body” (2005) sheds some light on how the spleen filters out bacteria, debris, and old or damaged blood cells from the blood.

Various other sources have also been consulted to elaborate on over a dozen spleen functions.

What is Heart

Ordnance Factory:

Is it true your immune system stands on the white blood cells?

The role of white blood cells (WBCs) is crucial in the defense of your body.

They are your body’s arms as they help kill germs.

If WBCs are your body’s arms and artillery, it is logical to call the spleen your body’s ordnance factory.

Also, note that the spleen function in body changes after birth.

During gestational age, it synthesizes blood cells and, in adult life, it serves as the major repository for lymphocytes – a type of white blood cells.

Frontline Defense:

In addition to housing lymphocytes, the spleen aids in the generation of an adaptive immune response to the foreign antigens.

Another rather stronger reason why you can call it the frontline defense is that it filters the blood and removes any germs or harmful foreign substances that have the potential to cause disease.

Spleen participates in the primary immune response to invading bacteria, viruses, parasites, or foreign particles.

In this way, the spleen is a strong defense against blood-borne pathogens.

That is why the removal of spleen increases the risk of infection.


Did you know? The spleen has quite different roles in the life of an individual before and after birth.

Before the birth, particularly during the first six months of intrauterine life, it functions as a major hemopoietic organ.

Hemopoiesis is the process of manufacturing blood cells. The spleen produces all types of blood cells.

And, after the birth of a human baby, the spleen switches its role from being a hemopoietic organ to an important and multifunction immune organ.

Blood Storage:

The role of the spleen in storing blood is so significant that it seems to be the primary function of this organ in the body.

Did you know? The spleen can store a huge quantity of blood when compared with its actual size.

In fact it can swell up to create a room for as much as 1 liter of blood!

The blood stored in the spleen can prove to be very valuable during emergencies like hemorrhage shock.

It can also help stabilize the blood volume by transferring excess plasma from the bloodstream into the lymphatic system.

Cell Reservoir:

In addition to storing blood for use in case of emergency, the spleen also acts as a cell reservoir.

The white pulp of this immune organ is mainly lymphocytes.

The red pulp too contains a huge number of lymphocytes and macrophages – the ‘engulfing’ WBCs.

In certain diseases like leukemia or extreme anemia, the spleen can resume its role of producing blood cells.

This function is usually present during fetal life.


It is the kidneys that filter the blood.

Then what does spleen do in the process of filtration?

The fact is that both the organs filter the blood but with different objectives.

When you call the spleen a blood purifier, you’re referring to its job of taking out germs, toxins, old cells, and foreign substances from the blood.

It removes cellular residues, particulate matter, senescent RBCs, and other abnormal cells from the blood circulation.

While the kidneys mostly filter out waste products, the focus of spleen is on eliminating things that have the potential to cause disease.

Fighting Infection:

The job of the spleen in fighting infection in post-gestational age is as crucial as the production of blood cells in fetal life.

Its role in preventing infection is manifold.

First, as the largest lymphoid organ, it houses lymphocytes, which deal a deadly blow to the disease-causing particles.

Second, it rids the body of its debris of old cells and other substances that are injurious to health as the blood flows through it.

Third, it synthesizes antibodies that provide incredible assistance in warding off infections.


The spleen is also involved in the synthesis of the proteins like tuftsin and properdin.

These proteins act as opsonins in countering an infection or a disease.

An opsonin may be an antibody or some other particle, which binds with foreign microorganisms or cells to make it easy for the phagocytes to engulf them.

Antibodies Synthesis:

In its capacity as an immune organ, the spleen produces antibodies against several types of microorganisms.

The antibodies include those against the polysaccharide encapsulated bacteria like pneumococci.

Wiping Out Old Cells:

When the old blood cells are no more functional or needed by the body, they start accumulating in the blood and affect the transport of various substances.

They may also cause diseases if not removed timely.

The red blood cells or erythrocytes in your body have an average life span of (100 to) 120 days.

So, your body calls the spleen out for wiping out old, unwanted red blood cells and leukocytes. The spleen destroys all such cells.

When the spleen is removed surgically due to any irreversible damage, increased numbers of abnormal RBCs are seen in blood smears.

Destroying Old Platelets:

Though not designated as blood cells, platelets play a significant role in the body.

These cell fragments are found in large numbers and involved in the process of blood clotting.

But the old platelets need to be destroyed before their ultimate removal out of the body.

And this is done by the spleen.


In the process of culling, the spleen selectively removes abnormal RBCs from the blood.

It occurs during the open type of microcirculation.

While engaged in culling, the red pulp highly sensitively clears out the foreign materials from the blood.

Numerous macrophages, residing in the splenic cord, take part in this activity.

Here it’s noteworthy that there are 3 types of microcirculation in your spleen, i.e. open circulation, closed circulation, and microcirculation to the white pulp and marginal zone.


In addition to executing the culling function, open microcirculation in the spleen also carries out the pitting function.

Pitting refers to the elimination of intraerythrocytic inclusions without causing damage to the red blood cells.

Narrow slits of the sinus are used in the pitting function.

Removal of Howell Jolly Bodies:

The remnants of the old red blood cells’ nuclei are called Howell Jolly Bodies.

Did you know?

There is no other organ in the body that could remove the remnants of the RBC nuclei except the spleen.

So, in the individuals without a spleen or having a non-functional spleen (asplenia), Howell Jolly Bodies can be seen in the peripheral blood.


When a living-cell engulfs or eats up another living cell or particle, the activity is called phagocytosis.

The macrophages present in the spleen – called the splenic macrophages – are engaged in phagocytosis.

These ‘engulfing’ white blood cells (macrophages) eat up senescent erythrocytes (red blood cells).

For this reason, they are also called scavengers.

However, the role of macrophages in controlling infections like blood-stage malaria has also been recognized.

Protection of Lungs:

Splenectomy exposes the patients to various infectious and non-infectious diseases.

And they could be severe and life-long.

Such complications include pulmonary vascular disease or pulmonary hypertension, pneumonia, and pleural effusion.

Disorders of the Spleen:


It is the abnormal enlargement of the spleen.

Did you know?

When the spleen is diseased, it can be 10 times larger than its normal size!


The causes of splenomegaly include:

  • Parasitic infection such as malaria, and kala azar (black fever or Dumdum fever)
  • Chronic tuberculosis
  • Typhoid, septic shock, and infective endocarditis
  • Rheumatoid arthritis and systemic lupus erythematosus
  • Portal hypertension and liver diseases
  • Lymphomas, anemia, and leukemia


It is the surgical removal of the spleen.

Splenectomy is usually performed due to severe trauma or rupture of the spleen.

In the long run, there is an increased risk of overwhelming infections after the surgical removal of the spleen.

The number of platelets in the blood is also increased immediately.

Spleen Facts:

  • Did you know? The splenic function can return even after the spleen has been removed!
  • The spillage of the splenic tissue on the peritoneal surface during splenectomy can lead to the auto-transplantation of the organ!
  • While the lymph nodes filter lymph, the spleen – an enlarged lymph node – filters blood.
  • Though the largest organ of the lymphatic system, the spleen plays an accessory role in the system. The thymus and the bone marrow are the primary organs of the system.
  • The removal of the spleen can improve anemia for most people with pyruvate kinase deficiency!
  • About 25% of the body's T lymphocytes and 15% of B lymphocytes are present in the spleen.
  • Wandering spleen is a rare spleen condition in which the organ migrates from its normal position to an abnormal location in the abdomen!
  • A wandering accessory spleen is an additional spleen in the body that dislocates from its normal position to an abnormal one.
  • The red pulp of the spleen, acting as a filter, is engaged in the removal of old/aged red blood cells and other matter.
  • Did you know? Your spleen receives about 5% of the total cardiac output every minute.
  • 90% of the blood entering the spleen is emptied into the open circulation of the “red pulp”.
  • The white pulp of the spleen is involved in the immunological function. And it can be divided into two zones –the B lymphocyte zone and the T lymphocyte zone.

About the Author

Posted by: M. Isaac / Senior writer

A graduate in biological sciences and a PhD scholar (NCBA&E University, Lahore), M. Isaac combines his vast experience with a keen and critical eye to create practical and inherently engaging content on the human body. His background as a researcher and instructor at a secondary school enables him to best understand the needs of the beginner level learners and the amateur readers and educate them about how their body works, and how they can adopt a healthier lifestyle.

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