Chapter 11 The Blood 329 Copyright Goodheart-Willcox Co., Inc. cells to the site of an injury or infection), play a role in allergic reactions, or destroy parasitic worms. Classifying White Blood Cells There are five different types of white blood cells. Each type varies by size, appearance, and function. · neutrophils · eosinophils · basophils · lymphocytes · monocytes contains about 4,300 to 10,800 white blood cells per cubic millimeter. For every 1 white blood cell in the blood, there are approximately 700 red blood cells. Although RBCs far outnumber WBCs, the ratio of 1 WBC for every 700 RBCs is a bit misleading, because WBCs can leave the blood, but RBCs cannot. Through a process called diapedesis, WBCs, primarily neutrophils and cytokines, pass through spaces in the capillary walls as they move from the blood to infection sites in body tissues. The ratio stated above does not include WBCs that are in the body but not in the blood, so it does not represent the true number of WBCs in the body. As stated earlier, WBCs play an important role in the body’s defense systems and immune response. When a foreign microorganism, such as a virus or bacterium, is detected, the body dramatically increases WBC production. Within a matter of hours, the number of WBCs doubles to battle the infection. Generally, WBCs have a lifetime of 13–20 days. WBCs have an arsenal of weapons that they use to fight infection. Some WBCs, such as neutrophils, monocytes, and eosinophils, engulf and digest pathogens and other microorganisms through phagocytosis (Figure 11.7). Other WBCs produce antibodies, intensify the inflammatory response (which increases swelling and draws more white blood Training at High Altitudes Many athletes believe that training at high altitudes can improve their performance at sea level in endurance events. This belief stems from the increase in red blood cell production that occurs at high altitudes due to increased erythropoietin. A greater number of RBCs improves the blood’s oxygen-carrying capability and the performance of muscle. What athletes do not realize, however, is that living at high altitudes decreases the intensity at which they are able to train, thereby negating any of the beneficial effects of having more red blood cells. VO2 max, the best test to measure cardiopulmonary (aerobic) fitness, is defined as the amount of oxygen consumed by the tissues during maximal intensity exercise. Most runners, cyclists, and other athletes who compete in endurance events strive to achieve the highest VO2 max possible. For every 1,000 feet above about 4,920 feet (1,500 meters), VO2 max decreases by 3%, so high-intensity training is impaired. Instead, athletes should consider living at high altitudes and training at lower altitudes. This practice is known as “living high and training low.” Research sug- gests that an athlete’s sea-level performance can be improved by living at a moderately high altitude and engaging in high-intensity training at a lower altitude. Living at a moderately high altitude for a certain period of time causes the kidneys to secrete more erythropoietin, a hormone that causes bone marrow to increase red blood cell production. A recent study on elite runners shows that four weeks of “living high” (at moderately high altitudes of 8,100 ft or 2,500 m) and “training low” (at altitudes of 4,100 ft or 1,250 m) can significantly improve the ability of muscles to utilize oxygen during maximal intensity exercise. Research shows that erythropoietin levels nearly doubled during the four-week altitude training program, which is thought to be the reason for the improved performance. In fact, oxygen utilization improved by 3%, and the runners’ 3,000-meter race times improved by 1.1%. These are significant improvements for athletes who were already considered to be the best runners in the United States. Focus On 1 White blood cell engulfs enemy cell (bacteria, dead cells) Enzymes start to destroy enemy cell Enemy cell breaks down into small fragments Indigestible fragments are discharged 1 2 2 3 3 4 4 © Body Scientific International Figure 11.7 Phagocytosis. Ch11.indd 329 5/3/2019 9:44:33 AM