A Fascinating First Person Tour of Human Anatomy
Think big when you think about me. I am a transport system with 75,000 miles of route - more than a global airline. I am also a garbage man and delivery boy with 60 trillion customers - that’s 17,000 times the number of people there are on earth. My customers are the cells in Yossel’s body. I haul away their wastes and provide them with the essentials of life. I am Yossel’s bloodstream.
He thinks of me as a sluggish river, and is hardly aware of the frenzied activity under way within me at all times. In the second it takes Yossel to blink his eyelids, 1.2 million of my red cells reach the end of their 120-day life span and perish. In that same second, Yossel’s marrow, mostly in his ribs, skull and vertebrae, produces an equal number of new cells. In a lifetime these bones will manufacture about half a ton of red cells. During its short life, each red cell will make something like 75,000 round trips from Yossel’s heart to other parts of his body.
How do I get around Yossel’s body? Yossel’s heart is my main pump - and not a very good one as far as I am concerned. It pumps in surges, and it is therefore up to my big arteries to even the irregular flow, expanding with the pumping stroke, contracting between beats, so that blood arrives as a steady stream in my extremities. By the time the blood is ready to return to the heart through my veins, pressure has dropped to near zero. Left on its own, the blood would never get back.
Yet I keep it moving - from toes back to heart - aided by muscles outside my system. An awkward arrangement, but it works. As Yossel’s leg muscles contract, they squeeze veins and push blood upward (regularly spaced valves prevent backflow). That’s why walking is an excellent stimulator of circulation. (If the valves leak, the veins are apt to stretch and become clogged with clotted blood. That’s a varicose vein - often painful, always troublesome.)
Basically, the fluid that flows through my intricate pipeline system consists of red cells, a bewildering array of leucocytes, or white blood cells - granulocytes, lymphocytes, monocytes - as well as platelets and a variety of other, soluble constituents such as cholesterol, sugar, salts, enzymes and fats, plus liquid plasma to float everything in. To assure safe blood volume and pressure, my liquidity must always be maintained at the proper level. To be on the safe side, I absorb virtually all the water that Yossel drinks - excreting any excess via urine, sweat and exhaled air. When water is in short supply, I conserve every drop and cry for help. That’s why the badly wounded always beg for water.
Everyone is familiar with my basic blood groups - O, A, B and AB. But my blood also contains a great variety of other factors (M, N, P, Rh, etc.), and new ones are identified all the time. There is a growing probability that Yossel’s blood may be quite as distinctive as his fingerprints, different from all other bloods on earth. In fact, it might be possible to take a blood sample from each person in a large stadium right now, and then a year from now take another sample and assign each fan his proper seat - on the basis of individual blood characteristics.
To distribute oxygen and food to cells, I operate like a municipal water-supply system. The heart pumps, blood is pushed through arteries that grow ever smaller, and finally the flow gets to the capillaries. These gossamer cobwebs, which link arteries and veins, are where the real action takes place.
Capillaries are so small that red blood cells must squeeze through in single file, occasionally even twisting themselves into odd shapes to make it. But in the second or so required for passage there is a whirlwind of activity. It’s like unloading a delivery truck, then reloading it with items no longer wanted. The big thing to be unloaded, of course, is oxygen, and carbon dioxide from cellular combustion is the main waste product reloaded in its place.
But the variety of other merchandise delivered to the tissues is amazing. The shopping lists of individual tissue and organ cells are by no means the same. One cell will want a smidgen of cobalt; others will call for minerals, vitamins, hormones, glucose, fats, amino acids or a simple drink of water. If Yossel is exercising, tissue requirements for just about everything increase enormously. His skin will flush - indicating that capillaries are operating at full capacity. When he sleeps, cellular food requirements become minimal and over 90 percent of his capillaries close down.
In the final analysis, Yossel is only as healthy as his capillaries. He thinks he breathes with his lungs, eats with his mouth, absorbs food from his intestine. Actually, he does these things in his capillaries. That’s why his physician always takes a hard look with an opthalmoscope at the retinas of Yossel’s eyes - about the only place in the body where capillaries are clearly visible. If they are clogged and distended, Yossel is in trouble.
To keep Yossel out of trouble, I am constantly alert for any deviation from normal. If I detect a blood loss - whether from a minor cut or a gunshot wound - I immediately rush platelets to the breach. Within seconds they make a temporary patch. Then I start moving up heavier defenses. Fibrin is an essential wound sealer. It isn’t normally present in my blood, for it would spell disaster, clogging arteries and bringing almost instant death. But I keep the essential raw material for fibrin’s production on hand at all times, and I also carry the enzymes necessary for the chemical conversion that produces it. I can start the process within seconds. After the emergency situation has thus been met, I can take my time about bringing up the raw materials for a permanent seal.
While any break in my pipeline system is a grave emergency, intruders - flu virus, pollen, splinters (the list is endless) - are even greater threats. I have weapons, called antibodies, against upward of a million of these invaders - each designed to attack just one individual enemy. It’s like having a million-man police force, with each officer specializing in one particular crime.
Perhaps the most striking feature of my antibodies is their memory. Although Yossel doesn’t recall the mumps he had when he was six - 41 years ago - my mumps antibodies do. Let particles of mumps virus slip into his body, and these antibodies will go after them like terriers after a rat. Yossel is unaware of the battle, but it is a fight to the death for both combatants. Once they have perished, certain white cells (phagocytes) come along to eat both. I am a tidy housekeeper and don’t like dead bodies cluttering up my premises.
In the time you take to read this sentence, I will have received billions of replacement antibodies. If it were not for the protection they afford, even the most minor infections could be deadly for Yossel.
Since my requirements are so exact, it is little wonder that I am prey to a host of ills. My arteries may harden with calcium infiltration to become as hard as clay pipestems. Fatty deposits collect. These stopped-up, or occluded, arteries can then cause everything from gangrenous toes to stroke or fatal heart attack. Let my sugar (glucose) content rise too high and Yossel has diabetes. Let it fall too low and he has hypoglycemia - with palpitation, pallor, sweating, dizziness, weakness. Too few or defective red cells result in anemia.
My white-cell count can drop dramatically in a condition called agranulocytosis. Death may follow in a few days if antibiotics don’t prevent infection until recovery occurs. Or, there may be too many white cells - counts rising from a normal 6000 to 8000 per cubic millimeter of blood to 100,000 or more. This is what happens in leukemia. Then too, if my clotting mechanisms are awry, hemophilia or purpura or other bleeding disorders can result.
Can Yossel do anything to ease my burdens? A great deal. He can watch his blood pressure - when it is too high, I am under constant stress. Medication can take care of this, keeping pressure at safe levels. Exercise is an absolute essential to keep my blood moving properly. Diet is another matter. Too much fat is a proven life-shortener.
In sum, I require far more care than other tissues or organs. But I am worth it, since the health of all those other organs - and hence of Yossel himself - largely depends on me.