The most common cell in your bloodstream gives blood its red color and is thus called a red blood cell. Just one drop of your blood contains hundreds of millions of such cells.
When viewed through a microscope, they look like doughnuts with a depressed center instead of a hole. Each cell is packed with hundreds of millions of hemoglobin molecules is, in turn, a beautiful spherical structure made of about 10,000 hydrogen, carbon, nitrogen, oxygen, and sulfur iron, which give the blood its oxygen-carrying ability.
Hemoglobin facilitates the transport of carbon dioxide from the tissues to the lungs, where it is exhaled.
Another vital part of your red blood cells is their skin, called a membrane. This marvelous covering enables the cell to stretch into thin shapes so as to pass through your tiniest blood vessels and thus sustain every part of your body.
Your red blood cells are manufactured in your bone marrow. Once a new cell enters your bloodstream, it may circulate through your heart and body more than 100,000 times. Unlike other cells, red blood cells have no nucleus.
This gives them more space to carry oxygen and makes them lighter, which helps your heart to pump trillions of red blood cells throughout your body. However, lacking a nucleus, they are unable to renew their internal parts.
Thus, after about 120 days, your red blood cells begin to deteriorate and lose their elasticity. Large white blood called phagocytes consumes these worn-out cells and spit out the iron atoms.
The scarce iron atoms attach themselves to transport molecules that take them to your bone marrow to be used in the manufacturing of new red cells. Every second, your bone marrow releases two million to three million new red cells into your bloodstream.
If your trillions of red blood cells were suddenly to stop functioning, you would die within minutes.