The gastrointestinal system can be described under two complementary organizing schemes: an anatomical scheme that traces the sequential structures food passes through, and a functional or "engineering tube" scheme that treats the tract as a linear processing pipeline whose stations each perform one operation — mechanical size reduction, lubrication and hydration, acidification and grinding, emulsification, enzymatic hydrolysis, absorption, water recovery, and controlled elimination. The functional scheme is the more explanatory of the two because it states the purpose each station serves, and the two schemes are then mapped onto one another so that every functional operation is assigned to the organ or accessory gland that performs it. This overview belongs to gastrointestinal physiology within human physiology and serves as the organizing framework onto which the detailed mechanisms of digestion, secretion, motility, and absorption are subsequently attached.
The gastrointestinal system can be described under two complementary organizing schemes: an anatomical scheme that traces the sequential structures food passes through, and a functional or "engineeri…