Works T H E
OF HIS HANDS
Life Is in the Blood
W
e can’t see it, but we know it’s there, under our skin. If it weren’t, we’d be dead! Our blood—the rich, red stuff of life—flows continuously throughout our circulatory system, keeping us alive. But just how does it do this? Why is blood so important, and what exactly does it accomplish for us? Blood plays multiple roles in making life possible— one substance ingeniously designed to serve many purposes. Perhaps an imaginary scenario can help us to understand them. Imagine a young boy on the playground, playing a “pick up” game of basketball with some friends in the summer. Having been passed the ball by a teammate, he rushes through defenders toward the basket for a layup. On his way, he and another player collide and fall to the ground. The boys around offer their two friends a hand up and a pat on the back. Before resuming play, he notices he’s bleeding a bit at his elbow, but not much. He wipes off the blood, unworried, and rushes back into the game, grinning all the while. The young man may not realize it, but the remarkable design of human blood has played a crucial role in making his game (and his life) possible in at least five different ways—five tasks we all need blood to accomplish for us every day. Moving Goods and Making Trades Blood serves as the body’s transport system. Each of its cells—20 to 40 trillion of them—receives oxygen and vital nutrients continuously, and has waste products removed, by blood flowing through the vast, fibrous
28 Tomorrow’s World | September-October 2020
network of veins, arteries, and capillaries that run throughout the body. Our basketball player’s muscle cells are fed by the nutrients blood carries from the digestive system, as are the hormones that regulate and motivate his body. Adrenaline to increase his heart rate and ready his muscles, proteins to build and maintain his bones and tissues, and fuel derived from the breakfast he enjoyed earlier are all carried to his hungry cells, non-stop, every moment as he drives himself toward the basket. As he makes more demands on his muscles, they cry out for more oxygen to burn their fuel. His lungs take in air, and it is the blood—specifically, the highly specialized cells called erythrocytes or, more simply, red blood cells—that brings the oxygen where it is needed. These erythrocytes, manufactured in our bone marrow, look like smooth, symmetric disks, with a bowl-shaped indentation in the middle of each side. Unlike other cells in the body, erythrocytes have no central nucleus. They contain the protein hemoglobin, which “grabs” oxygen from the lungs and “gives” oxygen to other cells it contacts in its journey through the body, passing through even the most microscopic blood vessel so no cell is deprived of the oxygen it continually needs. Upon reaching a cell, the erythrocyte exchanges its oxygen for carbon dioxide, which the body’s cells produce as a waste product, and carries it to the lungs, which release it to be exhaled and deliver a fresh load of oxygen for the next trip. And along with carbon dioxide, blood carries other waste products to the liver and the kidneys, which “scrub” waste from the blood so that it can continue on its journey, transporting more material.
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