”I am Your Body”

THYMUS

     UNTIL RECENTLY I've been regarded as a kind of poor relation in your family of glands. Like your appendix I was looked on as an evolutionary leftover useless, nonproductive, a source of no good and possibly of trouble. How times change! All of a sudden I find myself the hottest item in medical research-the possible key to problems ranging from allergy and arthritis to cancer and aging. I am your thymus gland.

In appearance I am anything but glamorous - an insignificant looking little blob of yellow-gray tissue, about the size of a matchbook, nestled between your lungs just at the top of your breastbone. (you have probably sampled my relatives in a meal. The neck sweetbread from a calf is its thymus.) My size is -determined by age. I weigh a third of an ounce now. But I weighed twice that when you were born and six times that when you reached puberty.

In my new role as a glamour organ, I'm being called "the throne of immunity." What is immunity? Basically, it is the body's effort to recognize and destroy any intruder that might be a source of harm - and this includes just about everything: bacteria, viruses, the wrong type of blood, a splinter in the finger, fungi, cancer cells, poisons, transplanted skin, you name it. In a sense, your body is a fortress with troops instantly ready to attack any invader - anything that is non-you. I am a chief component of your defense force, which is, in its way, more complex than the defense system of any country. I support its many elements-the spleen, lymph nodes, bone marrow, tonsils, adenoids, maybe the appendix and possibly portions of the intestine.

Some idea of my importance is given by the fact that when you were in your mother's womb, I was larger than your heart, even larger than a lung. To a great extent you came into the world defenseless against disease-except for the immune factors passed from your mother's bloodstream, into you. And these would perish in a very short time. Had you been born without me - as infants are from time to time the most trivial infection would have become a threat to life. You would have been a runty, sickly little babe, and within a few months might have died.

Instead, with me, little you was soon ready to fight infection on your own. You had in-your bone marrow a host of microscopic white cells, "immature TMseedlings" of cells called lymphocytes. 'These fledgling '~warrior cells were passed to me via your bloodstream. It was my task to hurry them toward maturity, and then send them to the spleen, lymphatic system and other organs for final growing up. I also gave these organs hormonal stimulus to prod them into activity. Within days I had your little immune system shaping up. I've been running the system ever since.

These lymphocytes produced by me, and another group possibly produced somewhere in the intestine, are extraordinary performers-part detective, part killer. Representing a fourth of your white blood cells, they instantly recognize any potential enemy - a flu virus, a pus-forming staphylococcus, a thorn that has penetrated a finger. Immediately they sound a general, alarm.

Suppose you cut your finger and a minor infection follows. To my lymphocytes, nothing is minor. They start pouring out antibodies and call upon other cells to do the same. Each antibody is specific against a single invader - one for mumps, one for whooping cough and so on; you may have as many as a million different kinds. The antibodies attack and slaughter the invading microbes in the cut. Meanwhile, the lymphocytes have joined forces with phagocytes, other white cells in the blood that simply eat the bacterial debris. Your cut finger heals uneventfully. You think nothing of the matter, although actually, quite a Waterloo has occurred.

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