Metabolism

A collective term for all the chemical processes that take place in the body. It is divided into catabolism (breaking down of complex substances into simpler ones) and anabolism (building up of complex substances from simpler ones). Usually, catabolism releases energy, while anabolism uses it. The energy needed to keep the body functioning at rest is called the basal metabolic rate (BMR). It is measured in joules (or kilocalories) per square metre of body surface per hour. The BMR increases in response to factors such as stress, fear, exertion, and illness, and is controlled principally by various hormones, such as thyroxine, adrenaline (epinephrine), and insulin. (See also metabolism, inborn errors of; metabolic disorders.)