David Rogosin, age 12, of Brandon, Manitoba, Canada, for his question:
What use is the thymus gland?
Medical scientists working on the body's glandular system have come to realize that it is a balancing and control system. The various glands work together to harmonize vital processes of the entire body.
Medical researchers neglected the thymus gland while they investigated the thyroid, the adrenals, and other more obvious members of the body's endocrinal system. Now they have a very good reason to discover its mysterious functions. Heart and other organ transplants from one human body to another are making medical history. And it so happens that the function of the thymus plays a crucial role in the success of these sur¬gical miracles.
The thymus gland of an infant is as big as the baby's fist. It is two sacks of spongy tissue that hang from the neck area down in back of the breastbone. As the baby grows up, the gland shrinks to the size of a thumb and seems to have little to do during a person's adult life. However, the infant thymus was very busy manufacturing very special lymph cells coded to the vital proteins of the body. As it dwindled, these key cells were disbursed some to the lymph nodes, some to the spleen, others to the bone marrow.
These are master cells bearing coded blueprints of vital chemicals ¬plus the ability to issue orders to other cells. They have a sort of built¬ in suspicion of any chemical that happens to be different from the proteins that were present in the baby's body. Germs, poisons and proteins differ¬ent from those in the coded cells are called antigens. When foreign bodies of this sort enter the body, sooner or later a few samples are floated to one of the many master cells disbursed by the infant thymus gland.
A master cell analyzes an antigen and compares it with its coded pro¬teins. Then it creates a specially designed antibody that changes the antigen and makes it harmless. The master cell then issues instructions to antibody manufacturing cells to produce copies and more copies of the new weapon. As production increases, swarms of antibodies are released into the body's fluids. Each antibody that meets a germ, a speck of foreign pro¬tein or some other antigen merges with it, changes it and makes it harmless, The main function of the thymus gland is to code and disburse the master cells that carry on the body's defensive systems against enemy invasion.
Research biologists suspect that the coded cells may be keyed to the various shapes of protein molecules. An antibody may be designed to lock into an antigen and change its shape to one that is harmless. The problems of transplant surgery occur because the coded chemicals do not match those of another human body. The master cells from the thymus gland regard the transplanted tissue as a foreign invasion and try hard to reject it. Medical science is finding ways to modify this strict defense system.