Erythrocytes, Leukocytes & Thrombocytes

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  • 0:01 Types of Blood Cells
  • 0:45 Erythrocytes
  • 2:34 Leukocytes
  • 5:51 Thrombocytes
  • 6:32 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Blood contains three types of cells that carry oxygen, fight infection and stop bleeding. In this lesson, learn what these cells look like and how they function.

3 Types of Blood Cells

When you cut yourself, what makes the cut stop bleeding? What protects you from infection and helps fight off bacteria and viruses if you do get sick? When you breathe in oxygen, what carries it to the cells throughout your body, very far away from your lungs?

All of these things - and many more - are functions of your blood cells. In your blood, there are three types of cells. They're commonly known as red blood cells, white blood cells and platelets - and formally named erythrocytes, leukocytes and thrombocytes. These cells move throughout your body in your blood to carry oxygen, fight infections and stop bleeding if a blood vessel is damaged.


Erythrocytes carry oxygen to the cells and tissues in your body and are the most abundant type of cell in your body. About a quarter of all the cells in your body are erythrocytes. They are commonly known as red blood cells because of their color.

In fact, the prefix 'erythro-' comes from a Greek work that means 'red,' and in biology, '-cyte' means 'cell,' so an erythrocyte is literally a red cell. Just like all blood cells, erythrocytes are produced in your bone marrow, and you produce a lot of them! Every second, your bone marrow is producing over two million new erythrocytes. Once they enter your blood, erythrocytes are always in motion.

Each cell makes a complete circuit through your cardiovascular system about every 20 seconds. Because they move around so much, they are easily damaged and so each erythrocyte only lives about 100 days before being destroyed and recycled. A mature erythrocyte is a very small cell, only six micrometers in diameter, and it does not have a nucleus or many organelles. Almost all of the cytoplasm in an erythrocyte is full of hemoglobin, an iron-containing molecule that binds to and transports oxygen. When hemoglobin is bound to oxygen it changes colors. This makes the red blood cells look brighter and more red when they are in your arteries and have lots of oxygen and turn a darker blue-red color when they give up their oxygen and travel back to your heart in your veins.

Erythrocytes are also quite flexible because they have to bend to fit through tiny capillaries that are often smaller than the cells themselves.


In addition to erythrocytes, your blood also contains leukocytes. The word leukocyte is a combination of the Greek words for 'white' and 'cell,' so a leukocyte is a white blood cell. Leukocytes are immune cells that protect your body from infection, and they are found throughout your body, including your blood. Just like erythrocytes, leukocytes are made in the bone marrow. All leukocytes are nucleated cells that are a bit larger than erythrocytes, but they are not all the same. There are five general types of leukocytes that all have different functions.

About 60% of the leukocytes in your body are neutrophils. Neutrophils are the first cells to respond to an infection or injury. When your blood vessels are damaged or you are infected by bacteria, neutrophils will stick to the walls of your blood vessels and crawl between the cells lining the blood vessel into the surrounding tissue. There, they target bacteria and fungi and kill and eat them. Neutrophils are very short lived, often only surviving for a few hours before being recycled.

The next most abundant leukocyte, making up about 30% of the total number of leukocytes, are lymphocytes. Lymphocytes, which include B-cells, T-cells and natural killer cells, are part of the acquired immune system. They respond primarily to virus-infected and tumor cells by producing antibodies.

Antibodies are small proteins that cause the infected cells to stick together so they can be destroyed more easily. They are specific to each individual virus, and some lymphocytes, called memory cells, remember the viruses you have been infected with before and immediately start producing antibodies if you are exposed again. This prevents you from contracting the same virus twice and is the basis of vaccines.

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