Red Blood Cells
Red blood cells, known as erythrocytes, perform the most important function of all the blood cells - delivering oxygen from the lungs to the body's cells and bringing carbon dioxide, a waste product of normal cellular function, back to the lungs where it is exhaled.
Red blood cells make up almost 45 percent of the blood volume. The average adult has about 30 trillion red blood cells, or about one billion red cells in each two or three drops of blood. Red cells are very small. Each red cell is disc-shaped and biconcave and has a diameter of seven to eight microns (one micron is one millionth of a meter).
Red blood cells contain a protein called hemoglobin, which is red in color. Each red cell contains about 300,000,000 hemoglobin molecules. Hemoglobin contains the element iron, which is important in enabling the red cell to transport oxygen and carbon dioxide. The hemoglobin captures oxygen molecules as red cells pass through the lungs. Subsequently, as red cells pass through the body's tissue, the hemoglobin releases the oxygen to the cells. The empty hemoglobin molecules then bond with carbon dioxide or other gases that are produced as waste by the process of normal cellular function, transporting it away to the lungs where it is released and exhaled.
Red cells are very flexible and may be compressed or folded without breaking. This ability is important because it enables the red cell to pass through the capillaries, the tiniest blood vessels, in order to deliver oxygen to each individual cell throughout the body. The capillaries are so small that the red cells must fold and twist to flow through these tiny vessels in single file.
Over time, the red blood cells become worn out and eventually die. The average life cycle of a red blood cell is approximately 120 days.
Red blood cells are manufactured continuously in the bone marrow. As old red cells are removed from circulation, new ones are being made in the bone marrow and released into the blood system. The bone marrow produces about 17 million red cells per second. (In an emergency, the marrow can make red cells up to seven times more rapidly.) In this way, the body's supply of red blood cells is replenished continuously to maintain the needed amount of red blood cells.
Since the human body is designed to produce red blood cells continuously, it is safe for healthy adults to donate blood, which is then stored for use by patients who need a blood transfusion.
As living tissue, red blood cells and white blood cells are responsible for nourishing, cleansing and protecting the body. Since the cells are alive, they, too, need nourishment. Vitamins and minerals keep the blood healthy. A ll blood cells have a definite life cycle, just as all living organisms do. The various kinds of blood cells make up about 45 percent of blood.
When the human body begins to lose blood through a minor wound, the platelets help cause the blood to clot to control and stop blood loss. Because new blood cells are always being made in the bone marrow, the body can replace the lost blood. When there is excessive blood loss through a major wound, that blood may have to be replaced through a transfusion of blood donated from other people.
Everyone's blood is similar, but not quite the same. There are four major blood groups. Additionally, your blood may have the Rh factor, which makes it even more unique. Blood received through a transfusion must match your own. Patients who are scheduled to have major surgery may, under certain circumstances, make autologous blood donations (donations of their own blood) so that they have a perfect match.
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