Types of Blood Cells

Last reviewed by Editorial Team on February 8th, 2019.

An average person has more than 5 liters of blood in the body. It is important to have the right amount and component of blood as it carries essential nutrients and oxygen for the living cells to use.

The blood is also the one that takes away waste products in the body. It also plays an important role in fighting off infections. The primary functions of the blood are the following:

Transport oxygen and nutrients to various parts of the body.
It carries cells and antibodies that are helpful in fighting off infections.
It prevents blood loss by forming a clot in the injury site.
It regulates body temperature.
It removes waste products by bringing them to the kidneys and liver to filter so as only clean blood will be transported to different parts of the body. ^{(1, 2, 3)}

Blood consists of different components mainly the red blood cells (RBCs), white blood cells (WBCs), plasma, and platelets.

Let us discuss the different blood components in details.

Human red blood cell rbc

Image 1: Human blood consists of different components.
Picture Source: s.hswstatic.com

blood vessel

Picture 2: A blood vessel with various blood cells outlined.
Photo Source: image.slidesharecdn.com

#1 – Plasma

plasma

Photo 3: It is the largest component of the human blood in terms of the liquid part.
Image Source: onlinesciencenotes.com

It is the liquid part of the blood. It contains water, fat, sugar, protein, and salt. It is clear, straw-colored part of the blood.

It is the liquid part of the blood that remains after removing other blood components (red blood cells, white blood cells, and platelets). It is the largest component of human blood (about 55%).

Plasma performs a variety of functions such as:

It serves as a transporting medium for the cell.
It fights off diseases and plays an important role in blood clotting. ^{(3, 4)}

#2 – Red Blood Cells (RBCs)/Erythrocytes

rbc red blood cell

Image 4: A closer look at the red blood cell.
Picture Source: cdn5.vectorstock.com

They are the most abundant cells in the blood. In fact, about 45% of the total blood volume is red blood cell. It is bright red in color and has a biconcave disk shape with a flattened center. It looks like a donut.

The erythropoietin; a hormone produced by the kidneys controls the production of red blood cells. The RBCs start as immature cells in the bone marrow and it would take about seven days for them to mature and release in the bloodstream.

Red blood cells circulate around the body for up to 120 days. After which, the damaged and old red blood cells are removed from the circulation with the help of macrophages.

Red blood cells do not have a nucleus, which makes them more flexible. However, the lack of nucleus limits the life of RBCs as they travel through the smallest blood vessels.

The membrane of RBCs can get damaged leading to depleted energy supply. One of the essential components of RBC is hemoglobin. The RBCs get its red color from hemoglobin. Haematocrit measures the percentage of the whole blood volume in the red blood cells.

The hemoglobin in red blood cell is extremely important for oxygenation. It transports oxygen from the lungs to various parts of the body. A person who has a low hemoglobin level is anemic as characterized by paleness, shortness of breath, and being tired easily. ^{(3, 4, 5, 6)}

Quick facts about red blood cells

It is the most abundant blood cell accounting to about 45% of the total blood supply.
Its shape is similar to biconcave disc (round and flat) looks like a shallow bowl. The rim is thick and the center is sunken.
The diameter is about 6.2-8.2 µm.
It does not have a nucleus.
It can change its shape easily.
Red blood cells contain hemoglobin which contains iron giving the blood its red color.
It does not have the ability to repair itself.
Erythropoietin controls the production of RBCs.
RBCs have a lifespan of 120 days.
A human adult produces around 4 million red blood cells per second.⁽⁴⁾

#3 – Types of White Blood Cells/Leukocytes

types of white blood cell wbcs

Picture 5: The different types of white blood cells.
Photo Source: upload.wikimedia.org

The primary function of the white blood cells is to protect the body from infection. Their number is fewer compared to red blood cells. As a matter of fact, white blood cells account to 1% of the blood.

There are different types of white blood cells and they are the following:

Neutrophil/ Polymorphonuclear cells – It is the immediate response cell and made up 55% to 70% of the total white blood cell count. The bone marrow needs to create neutrophils every single day as each neutrophil lives less than a day.
Eosinophils – They play an important role during allergic reactions. They kill pathogens by releasing toxins from their granules. Eosinophils make up 2.3% of white blood cells. Their lifespan is 8 to 12 days.
Basophils – They account 0.4% of white blood cells. They can live for a few hours to a few days. They play an important role in allergic reactions. They combat hypersensitivity reaction in the bloodstream by secreting an anticoagulants and antibodies. It contains histamine and secretes heparin. Histamines dilate blood vessels bringing more immune cells to the injury site. Heparin serves as anticoagulant that prevents blood clotting.
Monocytes – They are young white blood cells circulating in the blood. Once they mature, they become macrophages and will eventually leave the blood and migrate into the tissues. They play an important role during infection as they provide immediate defense by engulfing and digesting pathogens before other types of white blood cells reach the injured site.
Lymphocyte – there are two types of lymphocytes; t lymphocytes and b lymphocytes.

T lymphocytes – They regulate the function of other immune cells. They also attack infected cells.
B lymphocytes – They make antibodies that target bacteria, viruses, and other foreign substances. ^{(2, 6, 7, 8)}

#4 – Platelets

inactivated and activated platelets

Photo 6: The inactivated and activated platelets.
Image Source: upload.wikimedia.org

They are irregularly shaped fragments of the cells and they circulate in the blood until such time they are activated to form a blood clot.

It is important to maintain a normal level of platelet as too high or too low platelet count can have a detrimental effect on the body. A significantly low platelet level is called thrombocytopenia, which puts you at risk for bleeding.

An abnormally high level of platelet is called thrombocythemia, which leads to the inappropriate blood clot formation. It deprives vital organs of the body of blood and oxygen leading to heart attack, stroke, and eventually, death.

Quick facts about platelets

It does not have a nucleus.
It does not reproduce.
It is a small fragment of bone marrow cell.
A healthy platelet level is between 150,000 and 400,000.^{(3, 9)}

What are some common blood disorders?

Anemia – It is caused by a low number of red blood cells as manifested by shortness of breath, especially with exertion, pale skin, and fatigue.
Aplastic anemia – It is caused by the inability of the bone marrow to produce red blood cells. A person with aplastic anemia should take the necessary medication, blood transfusion, and bone marrow transplant.
Leukemia – It is a cancer of the blood caused by high numbers of abnormal white blood cells.^{(1, 6, 9, 10)}

References:

https://en.wikipedia.org/wiki/Blood_cell
https://www.ncbi.nlm.nih.gov/books/NBK2263/
http://www.hematology.org/Patients/Basics/
https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentID=34&ContentTypeID=160
https://www.msdmanuals.com/home/blood-disorders/biology-of-blood/formation-of-blood-cells
https://www.roswellpark.org/blood-cell-levels
https://microbiologyinfo.com/blood-cells-types-functions/
https://www.texasheart.org/heart-health/heart-information-center/topics/blood/
https://study.com/academy/lesson/functions-of-red-blood-cells-white-blood-cells-platelets.html
https://www.merckmanuals.com/en-ca/home/blood-disorders/biology-of-blood/formation-of-blood-cells