Blood has been called the river of life, transporting various substances that must be carried to one part of the body or another. Red blood cells are an important element of blood. Their job is to transport oxygen to the body's tissues in exchange for carbon dioxide, which they carry to the lungs to be expelled. Red blood cells are formed in the red bone marrow of bones. Stem cells in the red bone marrow are called hemocytoblasts. They give rise to all of the formed elements in blood.
If a stem cell commits to becoming a cell called a proerythroblast, it will develop into a new red blood cell.
The formation of a red blood cell takes about 2 days. The body makes about two million red blood cells every second!
Blood is made up of both cellular and liquid components. If a sample of blood is spun in a centrifuge, the formed elements and fluid matrix of blood can be separated from each other.
Blood consists of 45% red blood cells, less than 1% white blood cells and platelets, and 55% plasma.
Review Date 1/9/2022
Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.