Wilderness Underfoot: Your Blood

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Healthy humans have enough blood, plus a little extra, to meet the demands of the human body.

Your blood provides the irreplaceable service of supplying oxygen, nutrients and hormones to the tissues inside your body. It also helps remove waste. Because it contains living cells, blood is considered to be alive. Blood cells are created within the marrow of large bones.

An average adult carries about 5 quarts of blood, while a child weighing 80 pounds has about 2.5 quarts. And a newborn baby weighing about 8 pounds has only 10 fluid ounces of blood. As you might expect, infants and children are more susceptible to the dangers of blood loss because they have much less of it than adults.

Losing 10 and 20 percent of your total volume of blood can cause a condition known as hypovolemia. The signs of hypovolemia are a racing pulse, a drop in blood pressure and paleness that is particularly evident in the forehead, lips and nail beds. People suffering from hypovolemia may feel dizzy or faint, nauseated or terribly thirsty. Excessive blood loss must be prevented because it can lead to death.

To keep your body alive and healthy, your blood relies on red and white blood cells, and on platelets.

The red cells provide fresh oxygen to living tissues. They also assist in gathering and carrying away the gas carbon dioxide, a waste product of living tissue. Red cells are able to carry out this function thanks to the iron-rich protein hemoglobin, which is capable of binding to oxygen. As blood is transported through the lungs, hemoglobin is oxygenated. Then, as red cells travel through your body, they release the oxygen and collect carbon dioxide.

The white cells defend your body against disease by attacking and devouring parasites such as viruses, bacteria and fungi. They are much less numerous than the red cells, and much more short-lived. While a red cell has a life of about 120 days, a white cell may survive up to a few weeks.

Blood platelets are sticky bodies that allow blood to coagulate or clot to stem the bleeding when you’re wounded.

The liquid in which all these blood cells flow is blood plasma. Plasma is composed of 96 percent water, as well as proteins, clotting factors, antibodies, hormones, and electrolytes or salts. Plasma makes up about 55 percent of your blood’s total volume.

Blood is especially well-suited to flow through the body’s vessels and spiderweb thin capillaries. It is pumped by the heart, nonstop, 24 hours a day, throughout your entire life—more than a million barrels in your lifetime.

From the July 19-25, 2006, issue

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