A diminution in the flow of bile quickly expresses itself in constipation.
Fat and protein stimulate the activity of the liver, while starches, if taken in excess, incline to overload it.
The food is forced along the intestinal tract by peristaltic or muscular relaxation and contraction waves, as in the stomach. As it is so forced, the nutrient elements, after being put into condition for absorption, are taken up through the villi of the intestinal walls by the portal veins and the lacteals of the submucous lining.
A larger proportion of food is digested and absorbed than was formerly supposed, and the excretions from the intestines are, in many cases, made up almost entirely of refuse, and of the catabolic waste of the system. In an ordinary mixed diet, it is stated that about ninety-two per cent. of the proteins, ninety-five per cent. of the fats, and ninety-seven per cent. of the carbohydrates are retained by the body.
In digestion, it is of the utmost importance that the muscular, mucous, and submucous coats, and the secreting glands of the stomach and intestines be kept thoroughly strong and active, that the digestive juices may be freely poured out, the nutriment be freely absorbed, and the food be moved along the digestive tract. The strength of any organ is gained through the nutriment in the blood; therefore, daily exercise, which calls the blood freely to these organs is imperative. Daily exercise should be directed to the vital organs. A walk for exercise is not sufficient.
Absorption of Food
The greater part of the food is absorbed through the intestines, yet some proteins which have been fully digested by the gastric juice, and certain fats, particularly the fats in milk, which are in a natural state of emulsion, may be absorbed through the walls of the stomach. However, the absorption through the stomach is small compared to that through the small intestine.
Diagrammatic Representation of Villus.