Body Temperature and Metabolism,sweat,Shiver,Body Temperature and Metabolism,1.1 heat production 1.2 Heat loss 1.3 Regulation of temperature,2.1 The definition of metabolism 2.2 Metabolic rate,Metabolism,Body Temperature,TEXT Body Temperature and Metabolism During every moment of our lives, our cells are breaking down food molecules to obtain ATP for energy-requiring cellular processes. Naturally, we are not aware of the process of cell respiration, but we may be aware of one of the products, energy in the form of heat. The human body is indeed warm, and its temperature is regulated very precisely, even in a wide range of environmental temperatures.,time-consuming effort-requiring,equipment-processing drawings,inspiration,expiration,perpiration,Body Temperature The normal range of human body temperature is 96.5-99.5 F (36-38C), with an average of 98.6 F (37C). Within a 24-hour period, an individuals temperature fluctuates 1-2 F with the lowest temperatures occurring during sleep.,Fahrenheit/ centigrade,At either end of the age spectrum, however, temperature regulation may not be as precise as it is in older children or younger adults. Infants have more surface area (skin) relative to volume, and are likely to lose heat more rapidly. In the elderly, the mechanisms that maintain body temperature may not function as efficiently as they once did, and changes in environmental temperature may not be compensated for as quickly or effectively. This is especially important to remember when caring for patients who are very young or very old.,Heat Production Cell respiration, the process that releases energy from food to produce ATP, also produces heat as one of its energy products. Although cell respiration takes place constantly, there are many factors that influence the rate of this process:,1. The hormone thyrxine (甲状腺素and T3), produced by the thyroid gland, increases the rate of cell respiration and heat production. The secretion of thyroxine is regulated by the bodys rate of energy production, the metabolic rate, itself. When the metabolic rate decreases, the thyroid gland is stimulated to secrete more thyroxine.,甲状腺峡部,As thyroxine increases the rate of cell respiration, a negative feedback mechanism inhibits further secretion until metabolic rate decreases again. Thus, thyroxine is secreted whenever there is a need for increased cell respiration, and is probably the most important regulator of day-to-day energy production. 2. In stress situations, epinephrine and norepinephrine are secreted by the adrenal medulla, and the sympathetic nervous system becomes more active.,Epinephrine increases the rate of cell respiration, especially in organs such as the heart, skeletal muscles, and liver. Sympathetic stimulation also increases the activity of these organs. The increased production of ATP to meet the demands of the stress situation also means that more heat will be produced. 3. Organs that are normally active (producing ATP) are significant sources of heat when the body is at rest. The skeletal muscles, for example, are usually in a state of slight contraction called muscle tone.,Since even slight contraction requires ATP, the muscles are also producing heat. This amounts to about 25% of the total body heat at rest, and much more during exercise when more ATP is produced. The liver is another organ that is continually active, producing ATP to supply energy for its many functions. As a result, the liver produces as much as 20% of the total body heat at rest.,The heat produced by these active organs is dispersed throughout the body by the blood. As the relatively cooler blood flows through organs such as the muscles and liver, the heat they produce is transferred to the blood, warming it. The warmed blood circulates to other areas of the body, distributing this heat.,distribute handbills,4. The intake of food also increases heat production, because the metabolic activity of the digestive tract is increased. Heat is generated as the digestive organs produce ATP for peristalsis and for the synthesis of digestive enzymes. 5. Changes in body temperature also have an effect on metabolic rate and heat production. This becomes clinically important when a person has a fever, an abnormally high body temperature.,clinical medical college,The higher temperature increases the metabolic rate, which increases heat production and elevates body temperature further. Thus, a high fever may trigger a vicious cycle of ever-increasing heat production.,Heat Loss The pathways of heat loss from the body are the skin, respiratory tract, and to a lesser extent, the urinary and digestive tracts. Heat Loss Through the Skin Since the skin covers the body, most body heat is lost from the skin to the environment. When the environment is cooler than body temperature (as it usually is), heat loss is unavoidable. The amount of heat that is lost is determined by blood flow through the skin and by the activity of swea