Nancy Jennings, age 12, of Newport News, Virginia, for her question:
Do we really have blue blood in parts of our bodies?
In days of yore, people thought that the basic biology of some human bodies was superior to others. Aristocrats were called "blue bloods" and thought to have veins full of a superior sort of blue blood, but actually their blood was not one whit bluer than anyone else's.
Some of the blood vessels of the circulatory system can be seen dimly through the flesh and skin. Chances are, you can locate one on the inside joint of your elbow and maybe trace its path down your forearm. This blood vessel appears to be a delicate shade of blue, suggesting that it carries a stream of blue tinted blood. But if your doctor sends you for certain lab tests, you are in for a surprise. The lab technician stabs a blood vessel with a hypodermic siphon and the sample extracted is red, blood red.
Do not, however, allow this to shatter your confidence in your powers of observation. At least one biological trick is used to fool you. The blood inside the vessel may indeed have been tinged with blue. But exposure to the air caused it to blush rosy red. Part of the trick is performed by a chemical called hemoglobin that abounds in the teeming blood cells. Its partner is ordinary oxygen that abounds in the ordinary air.
The molecule of hemoglobin has a natural fondness for molecules of oxygen. Basically it is a neat package of four iron atoms and four particles of a substance called heme arranged around a central particle of a chemical called globin. The heme and the globin give it its name. But its iron performs the trick that changes the color of blood. In the presence of oxygen, the iron in hemoglobin forms loose attachments with molecules of oxygen. When blood cells are loaded with supplies of fresh oxygen, they become bright red.
But the links that bind the iron and oxygen are fragile. Cells grab the oxygen from passing blood cells and swap it for their waste carbon products. These wastes cause chemical changes in the hemoglobin and tinge it wig a bluish color. When this bluish blood oozes from a wound, it comes in contact with the air. The iron immediate¬ly exchanges its waste carbon dioxide for a supply of fresh oxygen. The blood cells change back to red. Inside your blood stream, you have trillions of bright red cells bearing oxygen and billions of bluish blood cells bearing waste carbon dioxide. You have a network of arteries carrying oxygen rich red blood throughout your body and a network of veins carrying used, blue tinted blood back to the heart and lungs.
The body uses the red blue, blue red color change in the process of supplying its living cells with oxygen and removing, the waste products o£ their life activities. The used blue blood it sent to the right side of the heart and pumped to the lungs where it comes in contact with spongy air sacs. There it exchanges its wastes for fresh oxygen and turns bright red. The oxygen rich blood goes to the left chambers of the heart. Every heart beat pumps red blood from the left chambers on its way to nourish the body and also used blood from the right side to the lungs to be revived.