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D THE PHYSICOCHEMICAL BASIS OF ANIMAL FUNCTION AND AN INTRODUCTION TO CONTROL SYSTEMS Chapter 17. BODY COMPOSITION About 70% of the weight of the non-obese adult animal is water. Of this, 45% is intracellular, 17% is interstitial, and some 6% is in the circulatory system. Water has superb solvent properties, it is an ionizing medium, it is a good conductor, and it has a high specific heat and a high latent heat of vaporization. Water exchanges readily between body compartments, mainly by a process called diffusion, but filtration, which is pressure-driven exchange, contributes as well. Water flux rates are very high: 100 times the volume of a cell may be moving in transit through that cell every second. Chapter 18 will be devoted to the properties of water that are of physiologic consequence. 2007 version – page 126
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A. Chemical composition Much information is available about the chemical composition of the bodies of animals and humans. The following data, provided for illustrative purposes, apply to a healthy, non-obese 70-kg adult man. Elemental Composition Oxygen 46 kg Carbon 12 kg Hydrogen 8 kg Nitrogen 2 kg Calcium 0.9 kg Phosphorus 0.5 kg Potassium 0.2 kg Sulfur 0.2 kg Sodium 0.1 kg Chlorine 0.1 kg In addition to these macroelements, also depicted in Figure 17-1, there are trace quantities of magnesium, iron, manganese, iodine, zinc, cobalt, copper, selenium, molybdenum, fluorine, and many others. It is important to appreciate that muscle is the largest organ mass and that muscle, along with the skeleton and adipose tissue, make up about 75% of body weight (Figure 17-2). It is not always recognized that skin (the largest discrete organ) and blood contribute as much as they do, or that the brain and spinal cord are larger than any of the visceral organs. The dry weight of lipids in the body represents about 10% of body weight, or 7 kg of a 70 kg adult. This leaves 63 kg as lean (or nonfat) body weight. The term fat free body is frequently used and it is of particular importance in considerations of growth and the efficiency of growth. The nature and patterns of growth are described in Chapters 55 and 59. Figure 17-1. Elemental composition. Oxygen is by far the most abundant element in the body. Oxygen, carbon, hydrogen and nitrogen make up about 97%of the body. The remaining macroelements, a host of microelements, and those present in only trace quantities are, however, qualitatively very important. Figure 17-2. The organ masses. In adults, muscle is usually the major organ system with adipose and skeleton ranking second and third. In animals selected for growth rate and large mature size, adipose can become dominant over muscle. Note that the carcass – comprised of muscle, adipose and parts of the skeleton – accounts for somewhat less than the 75% shown here. Of special importance now is that the water
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This note was uploaded on 03/23/2009 for the course ANSCI 1110 taught by Professor Brucecurrie during the Fall '08 term at Cornell.

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