Blood Cell Types And Functions

Blood cells are found within the life-maintaining fluid that we call blood which runs through our bodies. Blood has a multiplicity of different purposes.

Blood Cell Types And Functions

It is responsible for carrying nourishment, electrolytes, hormones, vitamins and oxygen around our bodies. It is also responsible for dispelling waste and carbon dioxide away from our tissues. 

Blood cells themselves are produced during hematopoiesis and are mainly found within our bloodstream.

Blood cells account for 45% of our blood tissue when measured by volume, whereas the remaining 55% is accounted for by plasma, which is the liquid portion of the blood. Here, we look at each of the different kinds of blood cells found within the human body. 

White Blood Cells (Leukocytes)

White Blood Cells (Leukocytes)

White blood cells come in a variety of different shapes and sizes. Some contain a singular, large nucleus, whilst others may demonstrate nuclei with multiple lobes.

With some of these cells, packets of granules are carried in the cytoplasm and are subsequently known as granulocytes. Those which do not contain packets of granules are known as agranulocytes.

Despite their dissimilarities regarding appearance, all white blood cells have homogenous roles. They circulate blood around the body until they receive a signal that an area of the body has been compromised. 

White blood cells are created in the bone marrow from multi potent cells called hematopoietic stem cells. They are present in all areas of the body, including the bloodstream, the lymphatic system, and connective tissue.

They make up the majority of the immune system, with 4500-11,000/mm3 cells present, however, they only account for around 1% of the blood. 

White blood cells present in the human body include leukopenia, which is a low white blood cell which is caused by damage to the bone marrow as a result of things such as chemotherapy, radiation, or various medications.

Leukocytosis is a high white blood cell and can be caused by a variety of different conditions, which include inflammatory diseases and a range of infections. 

In terms of range, there are five different types of white blood cells found in the human body.

These include Neutrophils (granulocytes), Eosinophils (granulocytes), Basophils (granulocytes), Lymphocytes (non-granulocytes) and finally, Monocytes (non-granulocytes).

Neutrophils (Granulocytes)

Neutrophils are also known as polymorphonuclear cells because they carry a nucleus with an irregular shape (morph) which contains many (poly) lobes. They are medium in size, with a diameter of 10–12 μm. 

The most common of all the white blood cells, they account for 62% of leukocytes, with 2000 to 7500 cells per mm3 found in the bloodstream. Their life span ranges from 6 hours to a couple of days. 

The Function Of Neutrophils

The primary function of neutrophils is to kill bacteria through a process called phagocytosis. Neutrophils also have the ability to kill multiple bacteria simultaneously, by releasing a bust of super oxides.

When bacteria infect the body, neutrophils are one of the first to respond and destroy invading microorganisms. 

Eosinophils (Granulocytes)

In terms of appearance, eosinophils contain very large granules. They are divided into two different lobes, making them a bi-lobed nucleus.

They have a diameter of 10-12μm and make up 40-400 cells for each mm3. Their lifespan ranges from 8 to 12 days. 

The Function Of Eosinophils 

Eosinophils are responsible for moving to areas of the body which have become inflamed. They respond to allergic reactions within the body and perform anti-parasitic and bactericidal functions.

By doing so, they help the body to overcome threats of disease and infection. They can help to trap substances, modulate inflammatory responses, and kill cells. 

Basophils (Granulocytes)

Regarding appearance, basophils can appear colorful as opposed to the other varieties of white blood cells. Their nucleus is pale and concealed by the granules it carries.

They have a diameter of 12–15 μm and make up 0-100 cells per mm3. They make up less than 1% of all white blood cells and make up the least amount of the human body. 

The Function Of Basophils

For a long time, researchers struggled to understand the function of basophils. However, we now understand that they perform similar functions to mast cells.

They play a part in detecting cancer cells in the body. They also release histamine if an allergic reaction occurs. 

Lymphocytes (Agranulocytes)

These white blood cells spear as rounder, smaller-sized cells. They contain a nucleus and are present with a diameter of 7-8μm. They make up approximately 30% of cells and their life span is extremely diverse, lasting from weeks to years. 

The Function Of Lymphocytes

The function of lymphocyte cells is varied. They can be divided into T and B cells. T cells are responsible for destroying other cells within the body that have turned malignant from diseases such as cancer.

B cells, on the other hand, provide humoral immunity and perform antibody production. Interestingly, lymphocytes can recognize and contain memories of previous invading bacteria. 


The appearance of monocytes can be compared to that of a kidney. They are the largest white blood cell in the body. With 200 to 800 monocytes per mm3, they account for 5.3% of the cells.

Their lifespan ranges from hours to days. When they exit the bloodstream, they turn into macrophages.

The Function Of Monocytes

Monocytes are a critical part of the function of the immune system. They eliminate damaged cells within the body, and so play a role in anti-inflammatory processes that occur when an immune response is triggered. 

Platelets (Thrombocytes)

Platelets are the smallest of the blood cells which do not have any color. These cells differ from the other cells as they have an absence of a nucleus. 150,000 to 400,000 are found in each microliter of blood in the human body. 

Function Of Platelets

Platelets are integral to the health of the human body. They control blood clotting when healing a wound and will stop it from continuing to bleed.

If the body experiences injury and is cut, the platelets form an adhesive function and attach themselves to the area that is injured. 

They will then secrete chemicals which signal other platelets to form at the site of the injury. They work together to promote blood clotting.

Employing a function called a coagulation cascade, they form a blood clot activating a cascade of proteins called clotting factors. This knits the injury and stops the bleeding, allowing the wound to heal. Platelets also have the ability to destroy bacteria. 

Red Blood Cells (Erythrocytes)

Red Blood Cells (Erythrocytes)

Red blood cells are responsible for the transportation of oxygen around our bodies. Every single second, 2-3 million red blood cells are produced in our bone marrow and circulated throughout our bodies.

They are the most common type of cell found in the blood, and each cubic millimeter of blood contains around 4-6 million cells. 

Their appearance is formed of a biconcave disc which is round and flat in shape. It can be compared to the appearance of a shallow bowl. The disk diameter is approximately 6.2-8.2 µm.

They do not possess a nucleus, and their rim is thick in appearance with a sunken center. 

The red blood cells are able to change their shape without breaking apart, however, they are not able to repair themselves.

It is the iron contained in the cells which gives them their reddish color, this comes from the hemoglobin contained in the cell which makes up for 33% of their makeup. 

It has been shown that 4 million new erythrocytes are produced every second in human adults, and our bodies can contain 20-30 trillion red blood cells at any point.

There is a discrepancy between males and females, with males containing 4.3-5.9 million/mm3 red blood cells and females containing 3.5-5.5 million/mm3. 


The primary function of white blood cells is to protect the body against infection. They are the cells which are responsible for upholding the immune system.

They protect the body from harmful invasions from bacteria, viruses, and parasitic infections. When the body is battling an infection, more white blood cells are produced as a result. 

Red blood cells, on the other hand, are responsible for the daily function of the body. They expel carbon dioxide as a waste product and carry oxygen from the lungs to the other areas of the body. 

Jennifer Dawkins

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