The Digestive System and the Liver
A physician once remarked that a great many people seem to spend about half their time getting food into their digestive tracts and the other half worrying about how that food is doing on its travels. The physician was exaggerating, but he made his point.
The digestive tract has essentially one purpose: to break down food, both solid and fluid, into a form that can be used by the body. The food is used as energy to fuel daily activities or to nourish the various tissues that are always in the process of wearing out and needing replacement.
A normally functioning digestive tract, dealing with a reasonable variety and quantity of food, is designed to extract the maximum benefit from what we eat. Urine and feces are the waste products—things from which our body has selected everything that is of use.
Our digestive system's efficiency and economy in getting food into our bodies, to be utilized in all our living processes, can be attributed basically to three facts.
First, although the straight-line distance from the mouth to the bottom of the trunk is only two or three feet, the distance along the intestinal tract is about 10 times as great—25-30 feet—a winding, twisting, looping passageway that has more than enough footage to accommodate a number of ingeniously constructed way stations, checkpoints, and traffic-control devices.
Second, from the moment food enters the mouth, it is subjected to both chemical and mechanical actions that begin to break it apart, leading eventually to its reduction to submicroscopic molecules that can be absorbed through the intestinal walls into the circulatory system.
Finally, each of the three main types of food—carbohydrates, fats, and proteins—receives special treatment that results in the body deriving maximum benefit from each.