metabolism /mətab″əliz′əm/ [Gk, metabole, change, ismos, process] , the aggregate of all chemical processes that take place in living organisms, resulting in growth, generation of energy, elimination of wastes, and other body functions as they relate to the distribution of nutrients in the blood after digestion. Metabolism takes place in two steps: anabolism, the constructive phase, in which smaller molecules (such as amino acids) are converted to larger molecules (such as proteins); and catabolism, the destructive phase, in which larger molecules (such as glycogen) are converted to smaller molecules (such as glucose). Exercise, elevated body temperature, hormonal activity, and digestion can increase the metabolic rate, which is the rate determined when a person is at complete rest, physically and mentally. The metabolic rate is customarily expressed (in calories) as the heat liberated in the course of metabolism. See also acid-base metabolism, anabolism, basal metabolism, catabolism.
