第七章 能量代谢
2011-06-08 18:25:25   来源：   作者：  评论：0 点击：

相差值在±10%～±15%以内属正常，如果相差值超过20%时，才有可能是病理情况。现举例说明BMR的测定法：
某受试者，女性，25岁，身高160cm，体重50kg，在基础状态下6min耗O2量为1.5L，混合食物，求该女性的BMR是多少？
1h耗O2量＝1.5L×10＝15L
1h产热量＝20.34kJ/L×15L＝305.1kJ
体表面积(m2)＝0.0061×身高(cm)＋0.0128×体重(kg)－0.1529
＝0.0061×160＋0.0128×50－0.1529＝1.46m2
体表面积为1.46m2，从而1 h每平方米体表面积的产热量，即BMR实测值为：
BMR＝305.1÷1.46=208.97kJ/(m2·h)
查表7-4可知，25岁女子的正常BMR平均值为146.5kJ/(m2·h)，受试者与正常BMR平均值比较超过正常值为：208.97－146.5=62.47kJ/(m2·h)
超出正常值的百分率数为：62.47÷146.5×100%≈42%，即＋42%
本例的BMR比正常标准值高42%，表示该女子在基础状态下的能量代谢明显增高，这是由于细胞代谢增强或机体的耗氧量增加所致。临床上常见于甲状腺功能亢进、嗜铬细胞瘤、白血病、恶性肿瘤等疾病。
二、测定BMR的临床意义
(Clinical significance measuring the BMR)
BMR是以每小时，每平方米体表面积计算的产热量，其单位是kJ/(m2·h)。凡影响能量代谢的因素均可使BMR发生变化。在生理情况下，BMR随性别、年龄等不同因素而发生变动。其他条件不变时，男子的BMR比女子高；幼年比成年人高；年龄越大，BMR越低。但是，在符合BMR测定的前提下，同一个体的BMR是相当稳定的。此外，妊娠期有不同程度的升高，禁食时常常降低。
测定BMR是临床上经常采用的一种辅助检查手段，以帮助诊断某些疾病。例如，甲状腺功能低下（简称甲低）时，BMR将比正常值低20%～40%；甲状腺功能亢进（简称甲亢）时，BMR可比正常值高20%～80%。因此BMR测定是临床诊断甲状腺功能的重要辅助方法之一。此外，肾上腺皮质和脑垂体功能异常时，BMR也随之异常；发热时，BMR也升高（体温每升高1℃，BMR一般增加13%）；阿狄森氏病、神经性厌食、肾病综合征等BMR将明显降低。
（海南医学院 符史干）
Summary
All vital processes involve myriad chemical reactions. The chemical processes of the body collectively constitute metabolism. The energy metabolism means the liberation, transformation and utilization of energy produced by the material metabolism in the body. Thousands of chemical reactions are involved but they fall into two categories: catabolic metabolism and anabolic metabolism.
The carbohydrates, fats and proteins may become the source of energy of the body. These foods can be oxidized in the cell, and in this process a large amount of energy is released . The animal organism oxidizes carbohydrates, fats and proteins principally generate CO2, H2O, and the energy necessary for life processes. CO2, H2O, and energy are also produced when food is burned outside the body. It has been pointed out that carbohydrates, fats and proteins can all be used by cells to synthesize large quantities of ATP, and that the ATP can in turn be used as an energy source for many other cellular functions, including synthesis and growth, muscular contraction, glandular secretion, nerve conduction, active absorption, etc. Energy is stored by forming high-energy phosphate bonds .The ATP and the creatine phosphate contain all high- energy phosphate bonds. Creatine phosphate can transfer energy in interchangeably with ATP .
Direct and indirect calorimetry are two methods of energy metabolism measurement .The metabolic rate can be determined by simply measuring the quantity of heat liberated from the body by a special calorimeter(direct calorimetry).Energy production can also be calculated by measuring the products of the energy-producing biologic oxidations－ie,CO2,H2O,and the end products of protein catabolism produced－or by measuring the O2 consumed .This is indirect calorimetry.
The metabolic rate is affected by many factors .The most important is muscular exertion. O2 consumption is elevated not only during exertion but also for as long afterward as is necessary to the O2 debt .The metabolic rate falls approximately 10~15 per cent below normal sleep, but increases above normal when a person is excited. Recently ingested foods also increase the metabolic rate because of their specific dynamic action. After a meal containing a large quantity of carbohydrates or fats, the metabolic rate usually increases only about 4%. However, After a meal containing large quantity of protein, the metabolic rate usually increases about 30%. Another factor that stimulates metabolic rate is the environmental temperature. When the environmental temperature is lower than body temperature, heat-conserving mechanisms such as shivering are activated and the metabolic rate rises. When the temperature is high enough to raise the body temperature, there is a general acceleration of metabolic processes .In addition, the metabolic rate is also related to body surface area, age, sex and hormones such as thyroid hormone, epinephrine and norepinephrine, growth hormone, etc.
Even when a person is at complete rest, considerable energy is required to perform all the chemical reactions of the body. This minimum level of energy required to exist is called the basal metabolic rate(BMR).Because the level of physical activity is highly variable among different individuals, measurement of the BMR provides a useful means of comparing one person's metabolic rate with that of another. The usual method for determining BMR is to measure the rate of oxygen utilization over a given period of time under basal conditions.

参考文献
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复习思考题
1．简述机体能量的来源及其ATP的作用。
2．间接测热法的基本原理是什么？如何测算机体的产热量？
3．影响能量代谢的主要因素有哪些？举例说明之。
4．测定BMR的基本条件是什么？有何临床意义？