Structure and Functions of the Body / A Hand-Book of Anatomy and Physiology for Nurses and Others Desiring a Practical Knowledge of the Subject

by Annette Fiske

From the cecum the intestine ascends in what is known as the [ascending colon] along the abdominal wall at the right to the under surface of the liver, where it turns in the hepatic flexure abruptly across the body to the left, passing below the liver, stomach, and spleen in the [transverse colon]. In the splenic flexure it turns down the left abdominal wall, the [descending colon] passing to the crest of the ilium, where there is another curve, the [sigmoid flexure], leading to the [rectum], which passes for six or eight inches down along the vertebræ, a little to the left, to the anus, the external opening. This opening is guarded by two sphincter muscles, about an inch apart, the internal and external sphincters. The coils of the small intestine lie below the transverse colon, covered mostly by the omentum. The splenic flexure is behind the stomach and below the spleen and is slightly higher than the hepatic flexure. The sigmoid flexure can be felt in the [left inguinal region] in thin people.

The fact that the rectum is somewhat to the left is of importance in childbirth because if the rectum is packed, it may turn the child’s head in the wrong direction.

No digestion goes on in the large intestine, the function being to dry by absorbing water. The movements are practically the same as those of the small intestine except that they are much less active. Fermentation makes the contents acid. By the time food reaches the rectum it has been thoroughly digested and has given up its nourishment. It is then expelled as waste matter or feces. Defecation combines the involuntary movements of peristalsis and relaxation of the sphincters with the voluntary aid of the abdominal muscles. The ano-spinal reflex, by which movements of the bowel are regulated, is in the lumbar enlargement of the cord.

The hemorrhoidal veins in the lower rectum are connected with both the systemic and the portal veins and have no valves so that, as they are subjected to much strain, they often become varicose and dilated. This condition is called hemorrhoids or piles. Obstruction of the intestine may be caused by the growth of a constricting band, by intussusception or telescoping of the intestine on itself, especially at the ileo-cecal valve, or by volvulus or twisting. Foreign bodies are sometimes found in the appendix but they are not usually the cause of appendicitis. Cancer of the intestine is common and its mass is apt to cause obstruction with all its attendant symptoms. It may necessitate an artificial anus. Hernia or rupture may also occur and the hernia may become strangulated.

Food and Metabolism.—Anything serves as food that replaces or hinders the loss to which the component parts of the body are liable. Proteins, carbohydrates, fats, some mineral matters, as salt and perhaps iron, and water are needed. The energy once expended by plants or animals in the formation of the materials which serve as food is set free in the body by the breaking up of these complex substances into their original elements, which are then recombined into the complex materials needed for the body’s life and growth. This process of building up complex materials from simple ones is known as anabolism and that of breaking them down as katabolism, while the two combined form the complete cycle of metabolism. Those foods have the best value that give up their energy most readily. For their combustion, heat, oxygen, and water are needed. Hunger indicates that the supply of material for katabolism has been used up and that more is needed, just as thirst indicates the need of the system for more fluids.

The proteins or nitrogenous foods include all animal foods except fats, fish, crustaceans, eggs, milk and its products, certain vegetables, especially the lentils, that is, peas and beans, and gelatine. The fats include various fats and oils commonly eaten. The carbohydrates are the starchy foods, as cereals, sugars, fruits, and most vegetables, in fact, practically all except the lentils. Various beverages and condiments have no great nutritive value but serve to stimulate the appetite and to excite the secretion of the digestive juices. Coffee, tea, and alcohol are stimulants.

The different classes of foods have different functions in the nourishment of the body. The proteins are primarily tissue-builders and also help somewhat in force production. The fats are essentially heat-producers, though they too help in force production. The carbohydrates are chiefly important as force-producers, though they also produce heat and to a certain extent save protein oxidation. Fat is formed by all three but only in small amount by proteins. So no one food can form the whole diet but there must be variety. Carbohydrates and fats are not sufficient for life, some protein is necessary. Carbohydrates are more digestible than fats but have less potential energy. Gelatine saves waste of nitrogen, though it does not increase the supply. Water and salts are not nutritive but they aid the body processes, the water helping to dilute and dissolve substances for digestion.

The end-product of the consumption of protein is urea, which is eliminated by the [kidneys]. Just where it is formed is unknown, but many think in the liver. A trifling amount of urea is also eliminated in the sweat and in the breath as well as in the feces. Proteins increase nitrogenous metabolism and also the metabolism of other foods, but the amount of nitrogen eliminated is just equal to that taken in. Probably some comes from the tissues themselves and not from the food. The oxidation of carbohydrates and fats is measured by the amount of carbon excreted. At first as much is given off as is taken in, but after a while the carbohydrate is stored up as glycogen in the liver and the fats are stored as fat.

The amount of food needed varies with the person’s size and occupation, less being needed for a child than for an adult and more for a hard-working man than for one who is doing less work. In general, 100 to 130 grams of protein, 40 to 80 grams of fat, 450 to 550 grams of carbohydrates, 30 grams of salts, and 28,000 grams of water is a fair amount.

Foods are cooked to make them more digestible and to develop their flavor, so that they will taste better. Cooking also kills germs and parasites that might be harmful. Meats should be cooked rapidly on the outside to coagulate the surface albumen and keep in the juices. The heat, besides coagulating the albumen, turns the tough parts to gelatine. In cereals the tough envelope of cellulose is broken up and in vegetables the tough fibrous parts are softened and made more digestible.