|MadSci Network: General Biology|
What color is blood …really ? Human blood is made up of a liquid part and a solid part. The liquid part, when it is still in the body, is called plasma. It is yellowish in color. It makes up about 50 - 60 % of our blood. The solid part is made up of cells; red blood cells, white blood cells and platelets. White blood cells and platelets have no color but appear white when they are grouped together, as when blood is separated in a centrifuge. Together they make up less than 1 % of the blood. They are pictured in text books as having a variety of colors. This is because they can be stained with various dyes after they are removed from the body then placed on a glass slide. Red blood cells are always red. Since RBCs make up about 40-45% of our blood, the blood is red. Red blood cells are red because they have a protein called hemoglobin which contains iron. Iron likes to bind oxygen. Oxygen combined with iron is red. The more oxygen iron has bound to it, the redder it is. It is true that some persons have "iron poor blood". In this case their red blood cells are less red than normal, but they are still red. The iron in the hemoglobin of red blood cells is what carries oxygen to every tissue in the body. Why some people may think that blood can be blue is probably because of the color of our veins, which may be visible near the skin's surface. They appear blue because they do not get as much oxygen as the other tissues. When the red blood cells go to the lungs, the iron in them picks up oxygen. Blood then goes to the heart and then to the rest of the body through vessels called arteries. The arteries appear reddish as do many other organs, because the iron in the blood gives up its oxygen to the cells that need it as the red blood cells travel throughout the body. By the time the blood is back on its way to the heart and then to the lungs it has less than half as much oxygen as it did before. The veins, therefore, do not get as much oxygen as the other tissues and they appear bluish. The bottom line is: blood is red.
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