As the food is absorbed through the walls of the alimentary canal, it is picked up by the rootlets of the mesenteric veins and by the lymph channels—the latter through the abdominal cavity are called lacteals. Nearly all of the fats are absorbed through the lacteals. The whitish color given to the contents of the lacteals, by the saponified fats, gives rise to the term “lacteal.”
Nearly all of the proteins and sugars pass through the mesenteric veins and the portal veins to the liver. Here the sugars are at once attacked by the liver cells and built up into glycogen as described on pages 151 and 159. A small portion of the proteins, however, do not go to the liver, but are passed directly into the lymphatics and thus into the blood stream, where they are again carried to the liver, and the urea is separated.
To sum up, the larger part of the sugars, starches, proteins, and fats is absorbed through the small intestine, a small amount being absorbed in the stomach and a very little through the large intestine. While some water and salts are absorbed in the stomach and small intestine, these are largely absorbed in the large intestine.
Economy in Food
It is economy to keep the digestive organs and the circulation and tissues strong, in order that all foods eaten may yield returns, instead of hampering the activity of the body.
The food which furnishes the most tissue-building substance and yields the most heat and energy, with the least refuse, is the economical food, provided it is varied enough to meet the psychical needs as well as the physical.
Whether or not a food is economical depends on the degree to which it stimulates the activity of the mind as well as the body. Preparation and serving here are as important as the material to be served.
Economy in food is a question into which many factors should enter. A cheap food is not always an economical food. Amount and keeping qualities, palatability, ripeness or unripeness, the age, habit, and occupation of the partakers, all have their share in the problem.