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Red Blood Cells, Platelets (stained purple), a T-Lymphocyte white cell (stained green), and a Monocyte white cell (stained gold) as seen through a scanning electron microscope. ©2000 Dennis Kunkel, Ph.D.

The scientific name for red blood cells is erythrocytes. They are formed in the bone marrow and are created by a stem cell. Red cells are the most numerous of all blood cells in the blood. They are produced at a rate of 4-5 billion every hour in an adult human!

When a red cell matures, it ejects its nucleus before entering the bloodstream.

It looks like a doughnut, but without a hole in the middle. Red cells are 7-8 microns in diameter. Yet, they are the heaviest particles in the blood.


Red blood cells contain hemoglobin, a protein that carries oxygen. Oxygen is known as O2. Each time we take a breath in, we are inhaling oxygen in the air.


The role of red cells is to absorb oxygen through the little alveoli in your lungs and deliver it to all the muscles, tissues and organs in your body.


To do this, they travel through large arteries and tiny capillaries. Sometimes the capillaries are so small, the red cells have to squeeze and bend themselves in half to get through in order to release their load of oxygen!


But that's only half the trip! After they deliver the oxygen, the red blood cells pick up a waste product called carbon dioxide, known as CO2. Then they make the return trip back to the lungs through the veins where the CO2 can finally be released. The body eliminates carbon dioxide every time we breathe out! Then, the red blood cells start the trip all over again.

Rory Says: "If you're wondering how long it takes to accomplish a round-trip... it takes, on average... only 30-45 seconds! We, red blood cells have a life span of about 120 days. Then we are removed from circulation by an organ called the spleen."

The hemoglobin makes the blood cells red.
— Gerardo,
high school student
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