Chapter9

　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 large amounts of energy. The animal organism oxidizes carbohydrates, fats and proteins principally to 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 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 form the body by a special calorimeter (direct calorimetry). Energy production can also be calculated by measuring the products of the energy-producing biologic oxidations－i.e.，CO2, H2O or by measuring the O2 consumed. This is indirect calorimetry and depends on knowledge of the fat and carbohydrate composition of the diet.
　 The metabolic rate is affected by many factors .The most important one is muscular exertion. O2 consumption is elevated not only during exertion but also for as long afterward as is necessary to replenish the O2 debt. The metabolic rate falls approximately 10~15 per cent below normal during sleep, but can increase above normal when a person is aroused. Recently ingested food also increases the metabolic rate . After a meal containing a large quantity of carbohydrate or fat, the metabolic rate usually increases by only about 4%. However, after a meal containing large quantity of protein, the metabolic rate usually increases by 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.

The temperature of human body includes core temperature and shell temperature. The body temperature in physiology means core temperature, i.e., the mean temperature of deep body. In fact, the body temperature is usually indicated by the temperature in the armpit, the mouth (under the tongue) or the rectum. These values normally vary from 36.0℃ to 37.4℃, or 36.4℃ to 37.4℃, or 36.9℃ to 37.9℃ respectively. Under normal conditions, the body temperature is easily affected by day and night, sex, age, muscle activity and other factors, but does not normally vary by more than 1℃.
　 Body temperature depends on the production and loss of body heat. The main organs of heat production in human body are the liver, the brain, the heart and the skeletal muscles. The production of heat occurs through basic metabolism and muscle activity and is controlled by neural and humoral factors. The heat is lost largely through the skin. The volume of heat loss from the body depends mainly upon the differences in temperature between the skin and the surroundings. The flow of blood to the vessels in the skin controlled by sympathetic nerves can regulate the skin temperature. Skin loses heat to the external environment by means of radiation, conduction, convection and evaporation. As such, heat loss is affected by the effective radiative area, thermal conductivity of the object, velocity of wind, humidity and sweating, etc.
　 Sweating is an active process of sweat gland activity. It is divided into thermal sweating and mental sweating. There are two types of sweat gland: apocrine gland and eccrine gland. The main sweating control centre is located in hypothalamus.
　 Thermoregulation includes autonomic thermoregulation and behavioral thermoregulation. Thermoreceptors are divided into peripheral thermoreceptors and central thermoreceptors. They can receive cold and hot stimuli. The information converges to the nervous center, especially PO/AH in hypothalamus. The efferent impulse changes the heat production and the heat loss so as to regulate the body temperature.
　 Fever, which means a body temperature above the normal usual range, can be caused by infectious and non-infectious factors. Pyrogens, which are some proteins and their breakdown products or lipopolysaccharide toxins, can cause the set point of the hypothalamic thermostat to rise. Then, more heat production and less heat loss drive the body temperature to a new level. When the body temperature rises to 40.6-42.2℃, the person is likely to develop heatstroke. Its main symptoms are dizziness, sometimes vomiting and delirium, and eventually loss of consciousness. At this time, the body temperature needs to be decreased immediately. By contrast, in hypothermia, the metabolic rate of cells will slow down and the energy consumption will decrease, which is beneficial to surgery. But if the body temperature is too low, it can be harmful to the body. At present, low temperature medicine is developing rapidly in the world.