Orexis

Orexis is a term used in medicine and psychology to denote appetite or motivational drive, particularly the appetite for food but also broader appetitive desires. Derived from the Greek orexis, meaning appetite or desire, the word can describe both subjective craving and the physiological processes that govern feeding behavior.

In clinical contexts, orexis is contrasted with anorexia, the loss of appetite. Disorders may involve diminished orexis (hypoorexia) or excessive craving (hyperorexia). Pharmacological language uses orexigenic to describe agents that increase orexis and anorexigenic for agents that suppress it. The concept encompasses both sensory desire and the hormonal and neural signals that regulate intake.

Neurobiological underpinnings involve multiple brain regions, notably the hypothalamus and limbic system. The lateral hypothalamus has long been associated with the regulation of feeding. Orexin (hypocretin) neurons in the lateral hypothalamus contribute to arousal and energy intake by promoting wakefulness and appetite. Hormonal signals such as ghrelin increase orexis, while leptin and insulin generally reduce it, via multiple pathways including neuropeptide Y and melanocortin systems.

Today, orexis is less commonly used in routine clinical language, with appetite and hunger predominating. It remains a technical term in some pharmacological, neurological, and historical contexts, and appears in dictionaries and certain psychopharmacology texts.