Dietetics for Nurses

by Fairfax T. Proudfit

Secretion of Water in the Stomach.—The secretion of water by the cells of the stomach is such, according to Taylor, as to produce chyme of quite constant consistency, the solid particles being held in suspension in the fluid medium.

Factors Influencing Gastric Digestion.—The factors influencing digestion in the stomach constitute all those mechanical, electrical, chemical, and psychical factors which stimulate or retard the action of the gastric juices. The movements in the stomach are involuntary, but their activities may be stimulated by the flow of gastric juice. Sleep retards digestion in the stomach by retarding the movements in the organ itself.

Stimuli to Gastric Flow.—The division and liquefaction of the food in the mouth hastens gastric digestion by making the food better fitted for the action of the enzymes in the gastric juice. The type as well as the character of the food acts as a stimulus to the gastric secretion.

Water is probably the best of all the agents for stimulating the secretion of gastric juice, while dextrin (toast, zwieback) and the extractives of meat likewise exert similar powers.

Retarding the Gastric Flow.—The nervous system, on the other hand, at times checks or entirely inhibits a flow of these juices. Worry, excitement, anger, fatigue, chill; each plays its part in promoting poor digestion in the gastric organ. As chemical factors, water and salts are the two necessary substances for gastric digestion, since the enzymes in the juices cannot act except in their presence.

Alkaline carbonates and fatty foods both check the flow of gastric juice, and retard digestion. The psychic factors which result in a stimulation of the secretory cells in the stomach are exerted through the sight, smell, and taste. One often hears the expression: “The food looked, smelled, or tasted so good that it made my mouth water.” This actually occurs; hence the secretion has been named appetite juice. This appetite juice acts as a direct stimulant to the cells in the mucous lining of the stomach, causing a flow of gastric juice. It cannot be said to cause digestion, but it certainly institutes that process, thus starting the whole digestional procedure.

Digestion in the Larger Intestine.—Science has proved that most of the nourishing part of the food ingested is digested and absorbed before it reaches the larger intestine. The two portions of the alimentary canal known as the small and large intestine are separated by the ileocecal valve. Cannon claims “that this valve is competent, that is, under normal conditions the food mass which passes through into the colon cannot be forced back into the small intestine.” The food mass sometimes contains materials which have escaped digestion, likewise some of the active enzymes which bring about their hydrolysis, in which case a certain amount of their digestion may continue in the large intestine.

So far, investigators have found no enzymes in the fluids secreted by the cells in the walls of the large intestine, but they have found an alkaline fluid which assists in completing the digestion of the foods which has started in other parts of the intestinal tract.

Absorption.—Absorption of food occurs in all parts of the intestinal canal, but the major portion of it occurs in the small intestines, the mucous membrane lining of which seems particularly adapted for this purpose. According to Taylor there is no absorption of fats, carbohydrates, or proteins in the stomach. Other investigators believe that some of the protein is absorbed and also some glucose in concentrated solution. However, the stomach cannot be considered of great value as an absorbing organ. Physiology teaches that the absorption of the products of digestion occurs by means of the millions of small projections or villi with which the intestinal wall is lined. These villi contain numerous capillary blood vessels and spaces known as lacteals. The former converge into the portal vein, the latter into the lymphatic vessels and thence into the thoracic ducts.

The Absorption of Fat.—The fats, as has been described, are split into their two constituents, fatty acid and glycerol. The former is dissolved by the bile to form soap; the latter is readily soluble in water. These constituents thus dissolved pass through the walls and recombine in the form of neutral fat droplets, probably during the passage through the walls, since they appear in this form in the cells. They pass into the thoracic duct and thence into the blood stream.