If blood didn't circulate through our bodies, carrying oxygen and nutrients, we wouldn't be able to live.
Blood is so important to life that the body constantly makes new blood.
To do this, the body must produce the liquid part of blood, called plasma, and the cells that float in it.
Plasma is made mostly of water and salts that we absorb through our digestive tracts everyday.
Its job is to deliver nutrients and water throughout the body.
Ninety-nine percent of the blood cells floating in plasma are red blood cells, which carry oxygen from the lungs to the rest of the body and give blood its red color.
The average life of a red blood cell is four months.
What Happens After That?
The spleen continuously destroys millions of old red blood cells, recycling the iron to make new red cells.