Chapter 32 - 32 Gas Exchange and Transport in Animals C H...

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Free-Diving Is Dangerous M any aquatic mammals can dive to great depths and stay submerged for some time. Yet they breathe air, just as we do, and there- fore can’t breathe when they dive—no oxygen tank is provided! The northern elephant seal ( Mirounga angustirostris ) has been observed diving to a depth of 1,500 m. In comparison, a free-diving human can only dive to about 163  m. The Weddell seal ( Leptonychotes weddelli ) typically dives to only 300–400 m, but stays submerged for up to 15 minutes. The limit for humans is about 3 minutes. Let’s look at how aquatic mammals, such as whales, seals, and dolphins, do it. First, they store oxygen before they dive. Blood doping (as when athletes get a blood transfusion before a competi- tive event) is natural to them because they have more blood cells and more blood per body weight than humans do. Not only that, their muscles are chock full of myoglobin, a respiratory pigment that specializes in keeping oxygen where it is most needed— namely, in the muscles. A special diving response occurs when aquatic mammals dive: (1) The heart rate slows (called bradycardia) to about one-half to one-tenth the normal rate. (2) The peripheral blood vessels con- strict, and the blood circulates to the heart and lungs only. (3) After the oxygen stored by myoglobin is used up, fermentation supplies ATP. The lactic acid produced is 32 Gas Exchange and Transport in Animals CHAPTER OUTLINE Animals Have Gas-Exchange Surfaces 32.1 Respiration involves several steps 650 32.2 Gills are an effi cient gas-exchange surface in water 652 32.3 The tracheal system in insects permits direct gas exchange 653 32.4 The human respiratory system utilizes lungs as a gas-exchange surface 654 Ventilation Precedes Transport 32.5 Breathing brings air into and out of the lungs 656 32.6 Our breathing rate can be modified 657 32.7 External and internal respiration require no energy 658 APPLICATIONS HOW LIFE CHANGES Evolution of Gas-Exchange Surfaces 650 HOW BIOLOGY IMPACTS OUR LIVES Questions About Tobacco, Smoking, and Health 655 HOW BIOLOGY IMPACTS OUR LIVES Respiratory Disorders 660 Human free-diving Elephant seal 648
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metabolized when the animal starts breathing again. (4) Finally, the spleen kicks in. In addition to cleansing the blood, the spleen acts as a storage area for red blood cells. As the water pressure increases during the dive, compression causes the spleen to release its supply of fully oxygenated red blood cells. This oxygen keeps the heart and brain going for a while longer. Many humans want to free-dive—and they do. How far can we go in copying the aquatic mammals? Although we do not store oxygen to any great extent, it is helpful to warm up before diving into cold water. This makes sure the muscles are getting O 2 -rich blood for as long as possible before the dive begins. Researchers also recommend that the mask not include the forehead—where cold receptors are located. Cold receptors help bring on the diving response that can also occur in humans. You can practice bringing on the diving response by
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