Thermoregulation
Mammals and birds generally maintain body temperature within a narrow range (36-38~C、for most mammals and 39-42℃ for most birds) that is usually considerably warmer than the environment.Because heat always flows from a warm object to cooler surroundings, birds and mammals must counteract the constant heat loss. This maintenance of warm body temperature depends on several key adaptations. The most basic mechanism is the high metabolic rate of endothermy itself.Endotherms can produce large amounts of metabolic heat that replace the flow of heat to the environment, and they can vary heat production to match changing rates of heat loss. Heat production is increased by such muscle activity as moving or shivering. In some mammals, certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP. This nonshivering thermogenesis (NST) takes place throughout the body, but some mammals also have a tissue called brown fat in the neck and between the shoulders that is specialized for rapid heat production. Through shivering and NST, mammals and birds in cold environments can increase their metabolic heat production by as much as 5 to 10 times above the minimal levels that occur in warm conditions.
Another major thermoregulatory adaptation that evolved in mammals and birds is insulation (hair, feathers, and fat layers), which reduces the flow of heat and lowers the energy cost of keeping warm. Most land mammals and birds react to cold by raising their fur or feathers, thereby trapping a thicker layer of air.
Humans rely more on a layer of fat just beneath the skin as insulation; goose bumps are a vestige of hair-raising left over from our furry ancestors.
Vasodilation and vasoconstriction also regulate heat exchange and may contribute to regional temperature differences within the animal.
For example, heat loss from a human is reduced when arms and legs coo] to several degrees below the temperature of the body core, where most vital organs are locateD、

Hair loses most of its insulating power when wet. Marine mammals such as whales and seals have a very thick layer of insulation fat called blubber, just under the skin. Marine mammals swim in water colder than their body core temperature, and many species spend at least part of the year in nearly freezing polar seas. The loss of heat to water occurs 50 to 100 times more rapidly than heat loss to air, and the skin temperature of a marine mammal is close to water temperature.Even so, the blubber insulation is so effective that marine mammals maintain body core temperatures of about 36-38℃ with metabolic rates about the same as those of land mammals of similar size. The flippers or tail of a whale or seal lack insulating blubber, but countercurrent heat exchangers greatly reduce heat loss in these extremities, as they do in the legs of many birds.
Through metabolic heat production, insulation, and vascular adjustments, birds and mammals are capable of astonishing feats of thermoregulation. For example, small birds called chickadees, which weigh only 20 grams, can remain active and hold body temperature nearly constant at 40℃ in environmental temperatures as low as -40℃--as long as they have enough food to supply the large amount of energy necessary for heat production.
Many mammals and birds live in places where thermoregulation requires cooling off as well as warming. For example, when a marine mammal moves into warm seas, as many whales do when they reproduce, excess metabolic heat is removed by vasodilation of numerous bl

LIFE、SUCCESSAN
D、SATISFACTION
1Life satisfaction, which can be defined as general happiness or well being, is related to several demographic and personal qualities. The factor of age is important because the elements that make up life satisfaction may differ from one age to the next. Income is more likely to predict life satisfaction among middle aged and older adults than among young adults. Health is a more significant predictor of happiness among older adults than among the young or the middle age
D、However, average levels of life satisfaction do not change significantly with age. Generally speaking, older adults are as satisfied with their lives as are younger or middle-aged adults.
2There is no single element that guarantees high life satisfaction for everyone who possesses it. Happiness seems to consist of many things that each person weighs differently, such as income, education, work, and relationships. However, certain factors are reliable predictors of life satisfaction. One such predictor is health, especially one’s perception of one’s own health rather than a doctor’s objective health assessment.Another predictor of life satisfaction is a feeling of being in charge of one’s own life and a sense of authority over one’s own decisions.Adults who feel that they have some choices and options are generally happier than those who feel that their lives are controlled by others or by fate or chance. For example, older adults who experience financial strain feel less life satisfaction mainly because the problem signals a loss of control over their lives.
3The largest predictor of life satisfaction appears to be the adequacy of social relationships, especially marriage and family relationships. The perceived quality rather than the quantity of social interactions is most strongly related to happiness. Satisfaction with one’s close personal relationships is more closely linked to overall life satisfaction than either demographic factors or satisfaction with other key aspects of adult life such as occupation. This is true even among highly educated men, who typically have a very high commitment to their work. The quality of social support available in one’s key relationships affects the ability to handle stress and life changes as well as one’s ongoing level of life satisfaction.
4Studies suggest that family background and early-adulthood resources are predictors of psychological health or success at midlife. People who age well are those who start out well. One study showed that the happiest and most successful middle-aged adults had grown up in warm, supportive, intellectually stimulating families. Well-adjusted or successful middle-aged adults began adulthood with more personal resources, including better psychological and physical health at college age. They also had been practical and well organized in college and had shown greater intellectual competence.
5However, no measure of early family environment or early-adult competence remained a significant predictor of psychological well being at the end of middle age. One study of men revealed that at the age of 65, there were no childhood or early-adulthood characteristics that distinguished between men who had turned out well and those who had not. However, what did predict success and well being at age 65 was the men’s health and adjustment at midlife. These results suggest that a successful adult life is not something preordained from childhood or early adulthood but rather something created out of the opportunities available over the course of one’s life. Late-life success is related more directly to midlife qualities or experiences. People who start out with certain advantages have a greater chance of experiencing further advantages; however, it is what one does with the experiences-both positive and negative-that determines long-term life satisfaction. The

您正在结束答题

请确认是否提交试卷？

继续做题确认提交