Ingestive behaviors

Ingestive behaviors encompass all eating and drinking behaviors. These actions are influenced by physiological regulatory mechanisms; these mechanisms exist to control and establish homeostasis within the human body. Disruptions in these ingestive regulatory mechanisms can result in eating disorders such as obesity, anorexia, and bulimia. Ingestive behaviors encompass all eating and drinking behaviors. These actions are influenced by physiological regulatory mechanisms; these mechanisms exist to control and establish homeostasis within the human body. Disruptions in these ingestive regulatory mechanisms can result in eating disorders such as obesity, anorexia, and bulimia. Research has confirmed that physiological mechanisms play an important role in homeostasis; however, human food intake must also be evaluated within the context of non-physiological determinants present in human life. Within laboratory environments, hunger and satiety are factors that can be controlled and tested. Outside of experiments though, social constraints may influence the size and number of daily meals. Body weight regulation requires a balance between food intake and energy expenditure. Two mechanisms are required to maintain a relatively constant body weight: one must increase motivation to eat if long-term reservoirs are being depleted, and the other must restrain food intake if more calories than needed are being consumed. The environment of early humans shaped the evolution of ingestive regulatory mechanisms, starvation used to be a greater threat to survival than overeating. Human metabolism evolved to store energy within the body to prevent death from starvation. Today, the environment now has an opposite effect on humans eating behaviors. With the widespread availability of food in today's society, concern has shifted from starvation to overeating. As food scarcity and availability have become less and less of a problem, food intake has increased. The increase of food intake by so many people is due primarily to a number of environmental factors. Main social environmental factors include: Along with social environmental factors, ingestive behaviors are also influenced by atmospheric environmental factors. Atmospheric factors include: The gastrointestinal system, particularly the stomach, releases a peptide hormone called ghrelin. In 1999 experiments have revealed that hunger is communicated from the stomach to the brain via this hormone peptide. This peptide can stimulate thought about food, and is suppressed after food is ingested. Nutrient injection into the blood stream does not suppress ghrelin, so the release of hormone is directed by the digestive system and not by nutrient availability in the blood. These blood levels of ghrelin increase with fasting and are reduced after a meal. Ghrelin antibodies or ghrelin receptor antagonists inhibit eating. Ghrelin also stimulates energy production and signals directly to the hypothalamus regulatory nucli that control energy homeostasis. Hunger is the result of a fall in blood glucose level or depriving cells of the ability to metabolize fatty acids—glucoprivation and lipoprivation, respectively, stimulate eating. Detectors in the brain are only sensitive to glucoprivation; detectors in the liver are sensitive to both glucoprivation and lipoprivation outside the blood–brain barrier. However, no single set of receptors is solely responsible for the information the brain uses to control eating. There are two primary sources of signals that stop eating: short-term signals come from immediate effects of eating a meal, beginning before food digestion, and long-term signals, that arise in adipose tissue, control the intake of calories by monitoring the sensitivity of brain mechanisms to hunger and satiety signals received. There are several sets of receptors located in the head: eyes, nose, tongue, and throat. The most important role of head factors in satiety is that taste and odor can serve as stimuli that permit learning about caloric contents of different foods. Tasting and swallowing of food contributes to the feeling of fullness caused by the presence of food in the stomach.