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“A view through a microscope clarifies the various components of blood but gives no picture of the daily frenzy encountered by each cell. Red cells, for example, never sit motionless. From their first entrance into the bloodstream they are pushed and shoved through rush hour traffic. Beginning the cycle at the heart, they take a short jaunt to the lungs to pick up a heavy load of oxygen. Immediately, they return to the heart, which propels them violently over the Niagara Falls of the aortic arch. From there, highways crowded with billions of red cells branch out to the brain, the limbs, and vital internal organs.

Sixty thousand miles of blood vessels link every living cell; even the blood vessels themselves are fed by blood vessels. Highways narrow down to one-lane roads, then bike paths, then footpaths, until finally the red cell must bow sideways and edge through a capillary one-tenth the diameter of a human hair. In such narrow confines the cells are stripped of food and oxygen and loaded down with carbon dioxide and urea. If shrunken down to their size, we would see red cells as bloated bags of jelly and iron drifting along in a river until they reach the smallest capillary, where gases fizz and wheeze in and out of surface membranes. From there red cells rush to the kidneys for a thorough scrubbing, then back to the lungs for a refill. And the journey begins anew.

A person can live a day or two without water and several weeks without food, but only a few minutes without oxygen, the main fuel for our hundred trillion cells. Heavy exercise may increase the demand for oxygen from the normal four gallons up to seventy-five gallons an hour, prompting the heart to double or even triple its rate to speed red cells to the heaving lungs. If the lungs alone cannot overcome the oxygen shortage, the red cells call up reinforecements. Instead of five million red cells in a speck of blood, seven or eight million will gradually appear. After a few months in the rarified atmosphere of Colorado’s mountains, for example, up to ten million red cells will fill each drop of blood, compensating for the thinner air.

The pell-mell journey, even to the extremity of the big toe, lasts a mere twenty seconds. An average red cell endures the cycle of loading, unloading, and jostling through the body for a half million round trips over four months. In one final journey, to the spleen, the battered cell is stripped bare by scavenger cells and recycled into new cells. Three hundred billion such red cells die and are replaced every day, leaving behind various parts to reincarnate in a hair follicle or a taste bud. *

The components of this circulatory system cooperate to accomplish a simple goal: nourishing and cleansing each living cell. If any part of the network breaks down—the heart takes an unscheduled rest, a clot overgrows and blocks an artery, a defect diminishes the red cells’ oxygen capacity—life ebbs away. The brain, master of the body, can survive intact only five minutes without replenishment.

*The body provides the energy for the red cells’ travels by employing the heart, an organ that deserves a book exclusively devoted to it. Primitive artificial hearts are now available, but I would like to see a government design specification sheet for a truly adequate replacement.

BIDS ACCEPTED FOR:

Fluid pump with 5-year life expectancy (2,500,000,000 cycles).

No maintenance or lubrication required.

Output: must vary between .025 horsepower at rest and short bursts of 1 horsepower determined by such factors as stress and exercise.

Weight: not to exceed 10.5 ounces (300 grams).

Capacity: 2,000 gallons per day.

Valves: each to operate 4,000-5,000 times per hour.”

From In His Image, by Dr. Paul Brand and Philip Yancey

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