Appetite

APPETITE (from Latin appetitus - desire), the sensation of the need to introduce food into the organism. The appearance of appetite does not always correspond to the actual need of the organism for food, and, conversely, an exhausted patient may not feel appetite, as occurs in a number of nervous and other diseases. The degree of appetite depends on the state of the nervous system at a given time. Food substances that are pleasant to the taste enhance appetite, while unpleasant ones weaken it. In the generation of appetite, a major role is played both by unconditioned reflexes (see) to food—taste sensations—and by conditioned reflexes (see) developed to various types of food. Conditioned stimuli in this case are the appearance, smell, taste of food, circumstances accompanying the meal, etc. Many phenomena associated with the appearance or disappearance of appetite were studied and explained by Academician I. P. Pavlov. He pointed out that the first trigger for the secretion of gastric juice is not at all the entry of food into the stomach, as was thought before him, but irritations originating from the oral cavity. In a dog with a severed esophagus, 3–5 minutes after the beginning of the so-called sham feeding, juice begins to be secreted, which Pavlov called "appetitive juice." A number of conditioned stimuli usually associated with the intake of food (the dinner bell, table setting, etc.) or artificially developed in an experiment cause appetite and the appearance of abundant appetitive juice, which serves as the "priming" (Pavlov) for the prolonged secretion of gastric juice. The mental life of animals and man is sometimes reflected very sharply in appetite. This provides the explanation for the individual characteristics of appetite in different persons. For the physician, appetite is of interest because its magnitude changes strongly (usually decreases sharply) in diseases of the gastrointestinal tract, many organs, and in infectious, nervous, mental, and other diseases. The decrease in appetite is termed anorexia (see), and the morbid increase in appetite is called bulimia (see). When appetite is weakened, the physician must artificially stimulate it if this appears possible, because without appetite there is no stimulus for the secretion of digestive juices and, consequently, digestion proceeds poorly, and the ingested substances are insufficiently digested and absorbed (for changes in appetite in various diseases, see the respective diseases).