• Wonderfully Made to Stay Alive
    Awake!—1988 | August 8

    • Your Internal River of Life

      The number of cells in the body is beyond human comprehension. A conservative estimate is 75 trillion​—a figure 15 thousand times higher than the population of our earth. For oxygen to reach each of these cells, a transport system more complex and efficient than that of any modern city is required.

      The body’s transport system consists of blood flowing through the heart, the arteries, the veins, and a network of smaller blood vessels. It is “a closed system of about 100,000 miles [160,000 km] . . . of tubing,” states the book The Human Body. According to that estimate, your blood vessels, if laid end to end, would reach four times around the earth.

      This vast network also transports tiny particles of food absorbed from the walls of your intestines. Thus the whole body is provided with food and oxygen, even the seemingly insignificant parts. Some five million hairs grow from your skin; yet a network of fine blood vessels is directed to the root of every hair. The care given to each tiny hair is something to wonder at. “Do not become fearful,” Jesus assured his disciples, “the very hairs of your head are all numbered.”​—Matthew 10:28, 30.

      The contents of the blood enable your body to make an estimated three billion new cells every minute. The growth of hair is a result of cells multiplying at the root. As old skin flakes off your body, new skin cells multiply beneath. As cells are scraped off the walls of your intestines, new cells are made to replace them. Every second, millions of red blood cells are made in your bone marrow!

      Naturally, all this activity produces a lot of waste. Again the bloodstream comes to the rescue by carrying away carbon dioxide and small waste particles. Large waste particles, such as dead cells, are consumed by white blood cells, which enter the tissues from the blood. Large numbers of these sanitary agents gather at the site of an infection to perform their task. Before medical science discovered these facts, the Bible expressed it simply: “The soul [or life] of the flesh is in the blood.”​—Leviticus 17:11, 14.

      Emergency​—Coping With Loss of Blood

      Did you ever sustain an injury that caused severe bleeding? Death could have resulted if you had lost too much blood. But most of the time, marvelous emergency mechanisms, which science cannot fully explain, help to avert such an outcome.

      When a blood vessel is severed, it contracts, thus reducing the flow of blood. A second mechanism quickly follows. Platelets in the blood become sticky around the site of the injury and clump together. Then threads of fibrin start forming in the wound. These bind the platelets into a clot that seals off the last trickle of blood.

      What happens, though, when the above mechanisms fail to cope? Massive bleeding triggers other mechanisms. Tiny receptors in the arteries quickly register any lowering of blood pressure. Messages are sent to the brain, which responds by causing blood vessels to constrict. At the same time, the brain commands the heart to beat harder. If the bleeding continues, the brain itself suffers from the effects and responds by intensifying these nerve reflexes. The heart rate may increase from the normal of about 72 beats per minute up to about 200. How effective are such mechanisms?

      The constricted blood vessels reduce the flow of blood to most parts of the body. This, together with the increased heart rate, maintains the blood pressure. “Yet by a beautiful device,” observes Dr. A. Rendle Short in his book Wonderfully Made, “the arteries of the brain are exempt from the generalized constriction.” The same is true of the arteries supplying the heart muscles. Thus, blood flows essentially normally through these vital organs. According to Professor Arthur Guyton’s Textbook of Medical Physiology, the above reflexes “extend the amount of blood loss that can occur without causing death to about two times that which is possible in their absence.”

      Meanwhile, other mechanisms operate to increase the volume of blood. As Dr. Miller explains in his book The Body in Question: “The most important priority is the restoration of fluid bulk. If the loss is sufficiently slow, the body can do this on its own behalf by diluting the blood. Fluids are withdrawn from the tissues; there is an automatic reduction in the output of urine and an increased intake of water by the mouth.”

      Although he favors blood transfusion in the case of hemorrhage, Dr. Miller admits: “The most immediate threat to life is not shortage of blood, as such, but an inadequate volume of fluid. . . . The administration of . . . plasma substitute, is an acceptable stop-gap in the early stages, since it imitates the natural tendency of the body to restore the bulk of the blood at the expense of diluting it.” Professor Guyton states: “Various plasma substitutes have been developed that perform almost exactly the same [circulatory] functions as plasma [the fluid part of blood].”

      The body also has a mechanism to make up for the shortage of oxygen-carrying red cells. As a television documentary “Accident” from The Living Body series explained: “Normally our bone marrow produces red cells at about 20 percent of its total capacity. This means that if there’s a sudden demand for red blood cells, we can step up the production rate about five times.”