Биология Camal. Adaptations to Thin Air просмотров - 277
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The camelis adapted to survive in a hot, dry and sandy environment. Adaptive physical features are the closable nostrils and long eyelashes, which help keep out wind-blown sand. The feet are broad and splay out under pressure, so reducing the tendency to sink into the sand. The thick fur insulates the body against heat gain in the intense sunlight.
Physiologically, the camel is able to survive without water for 6-8 days. Its stomach has a large water-holding capacity, though it drinks to replace water lost by evaporation rather than in anticipation of water deprivation.
The body temperature of a 'thirsty' camel rises to as much as 40 °C during the day and falls to about 35 °C at night. The elevated daytime temperature reduces the heat gradient between the body and the surroundings, so less heat is absorbed. A camel is able to tolerate water loss equivalent to 25 per cent of its body weight, compared with humans for whom a 12 per cent loss may be fatal. The blood volume and concentration are maintained by withdrawing water from the body tissues.
The nasal passages are lined with mucus. Duuring exhalation, the dry mucus absorbs water vapour. During inhalation the now moist mucus adds water vapour to the inhalated air. In this way, water is сonserved.
The role of the camel's humps in water conservation is more complex. The humps contain fat and are therefore an important reserve of energy-giving food. However, when the fat is metabolized during respiration, carbon dioxide and water (metabolic water) are produced. The water enters the blood circulation andwould normally be lost by evaporation from the lungs but the water-conserving nasal mucus will trap at least a proportion of it.
Prehistoric and contemporary human populations living at altitudes of at least 2,500 meters above sea level may provide unique insights into human evolution, reports an interdisciplinary group of scientists.
Indigenous highlanders living in the Andean Altiplano in South America and in the Tibetan Plateau in Asia have evolved three distinctly different biological adaptations for surviving in the oxygen-thin air found at high altitude.
Adapting to High Altitudes
The Andean and Tibetan plateaus rise some 4 kilometers above sea level. As prehistoric hunter-gatherers moved into these environments, they encountered desolate landscapes, sparse vegetation, little water, and a cold, arid climate.
In addition, early settlers to the high plateaus likely suffered acute hypoxia, a condition created by a diminished supply of oxygen to body tissues. At high altitudes the air is much thinner than at sea level. As a result, a person inhales fewer oxygen molecules with each breath.
Symptoms of hypoxia, sometimes known as mountain sickness, include headaches, vomiting, sleeplessness, impaired thinking, and an inability to sustain long periods of physical activity. At elevations above 7,600 meters, hypoxia can kill.
The Andeans adapted to the thin air by developing an ability to carry more oxygen in each red blood cell. That is: They breathe at the same rate as people who live at sea level, but the Andeans have the ability to deliver oxygen throughout their bodies more effectively than people at sea level do.
They have higher hemoglobin concentrations in their blood. Hemoglobin is the protein in red blood cells that ferries oxygen through the blood system. Having more hemoglobin to carry oxygen through the blood system than people at sea level counterbalances the effects of hypoxia.
Tibetans compensate for low oxygen content much differently. They increase their oxygen intake by taking more breaths per minute than people who live at sea level.
In addition, Tibetans may have a second biological adaptation, which expands their blood vessels, allowing them to deliver oxygen throughout their bodies more effectively than sea-level people do.
Tibetans' lungs synthesize larger amounts of a gas called nitric oxide from the air they breathe. One effect of nitric oxide is to increase the diameter of blood vessels, which suggests that Tibetans may offset low oxygen content in their blood with increased blood flow.