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Blood carries various substances that must be brought 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 is carried to and
eliminated by the lungs.
Red blood cells are formed in the red bone marrow of bones. Stem
cells in the red bone marrow called hemocytoblasts give rise to all
of the formed elements in blood. If a hemocytoblast commits to
becoming a cell called a proerythroblast, it will develop into a
new red blood cell.
The formation of a red blood cell from hemocytoblast 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.
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