Philip McCormack, age 12, of Portland, Me., for his question:
HOW DOES THE BODY PRODUCE BLOOD?
Modern scientists know enough about the blood to fill shelves of books. But their investigations have barely begun. Obviously, if the body's blood making processes were known down to the last detail, we could copy the recipe and make our own. This may or may not be possible, but certainly not in the foreseeable future.
The miraculous blood that flows through the body is one of the most complicated mysteries of nature. Scientists have probed and probed to learn just a few of its secrets.
Imagine, for example, 3 trillion living cells, too small for the human eye to see. They rush around at various speeds, each performing its own chemical activities. Their busy lives may last anywhere from a day to 120 days. Every second, some 2 million of them wear out, are scrapped and replaced with new ones. These busy little bodies are, of course, the various blood cells in the average human body.
These separate cells can survive only in the bloodstream, which is a pale yellowish liquid called plasma. This watery plasma is a very special blend of chemicals which must be adjusted from moment to moment to maintain the proper proportions. The basic liquid is water; the vital chemicals are extracted from our food by numerous complex chemical activities. The right doses of this and that are allowed to seep through the tissues into the veins.
The production of the floating cells is even more complicated, for different types are manufactured in different parts of the body. The majority of blood cells are mini red saucers with thick rims. These are manufactured in numerous small pockets, tucked away inside the hollow bones.
The odd shaped platelets are needed to stem the flow of blood from an open wound. Various white cells are needed to fight off invading viruses and bacteria. The platelets and certain white cells also are manufactured inside the bones. Other white cells are created in various lymph nodes.
All the materials for creating the plasma and its swarms of floating cells are extracted from the food we eat. These ingredients are produced in numerous small factories, assembled and reassembled to meet the body's needs from moment to moment.
Every moment, parts of the blood wear out and a complicated system is needed to dispose of them. In some cases, vital ingredients are saved and recycled. For example, when old red cells are broken down, their iron is saved to make new red cells.