MEDICAL 360 HOMK MURSING Ccntinitcd fiotn pas;e sog. Part 2 The Process of Digestion-The Digestive Apparatus-How Different Foods are Digested-The Importance of Mastication down on the right. side of the body. The large Now that we have considered the circulation of the blood and its purification in the lunps we can consider the subject of digestion. Digestion is the process by which the food is prepared to be absorbed into the blood The food that we eat has to be changed and altered until it forms part of the blood itself. Now, anyone can see that cutlets, potatoes, and bread- and-butter in no way resemble the red fluid which we call the blood, and which constantly is circu- lating through our tissues, bathing them with nourishment. This food has first to be cut into minute particles by the teeth and stomach. Secondly, to be dissolved and made soluble, so that it can pass through the fine membranes lining the stomach and intestines directly into the blood-vessels. Some food, such as sugar, for example, can be dissolved and made ready to be absorbed into the blood without any chemical change taking place. Starch, on the other hand, is not soluble in water, and therefore must be altered chemically — changed from insoluble starch into soluble sugar. Fat is broken up into verv minute particles, that is, it is " emulsified " before it is absorbed . Lean meat has to be broken up and altered by the digestive juices before it is taken up by the blood. In a later article we shall deal fully with the subject of diet. Here we need only say that foods are divided into five classes : 1. Carbo-hydrates — starches and sugars. 2. Fats : lard, butter, dripping, vegetable oils, etc. 3. Proteids : animal proteids, such as lean meat ; and vegetable proteids, such as cheese, egg albumen, lentils. 4. Mineral salts : such as common table salt, and the salts in fruit juice. 5. Water. Food first is taken into the mouth, where it is quickly churned by the muscles of the tongue and broken up by the teeth. At the same time it is acted upon by the digestive juice of the mouth, which is called the saliva. Then it is swallowed into the stomach, to be subjected to the move- ments of the stomach muscles and acted upon by the gastric juice. After a time it passes on to the intestines, where various juices fake their share in the process of digestion. Before going into this process in detail we must study the simple anatomy of the digestive system. The Digestive Apparatus The digestive apparatus consists of : 1. The mouth, with the teeth and the salivary glands. 2. The gullet, or oesophagus (a muscular tube passing from the mouth to the stomach). 3. The stomach, a pear-shaped organ lying to the left side, at the level of the waist, below the heart. 4. The small intestine, which is about 22 feet long, leading from the stomach. Into this opens the common bile duct, which receives bile from the livci and the pancreatic juice from the pancreas, two very important digestive juices. The small intestine lies in a convoluted mass and is con- tinued on into the large intestine. 5. The large intestine. At the junction of the small and large intestines the vermiform appendix is attached, a little worm-like organ which is affected in the disease called appendicitis. The junction of larg3 and small intestines is low intestine passes upward in the right flank, then crosses the abdomen about the level of the waist, then downwards in the left flank. The last part of it is called the rectum, or bowel, and it is the terminus of the digestive canal. The large intestine is about five feet long, and is much wider than the small intestine. Teeth Salivary Clauds a=;sophagtiS Pancreatic duct Biliary duct Ascending colon Cascum Transverse colon Descending colon Digestive System The Process of Digestion By " digestion " the food is converted into a milky fluid, which can be taken up by the blood- vessels. The process is partly physical and partly chemical, and its aim is to reduce the food to a state of solution, so that it may pass through the thin walls of the vessels into the blood. The chief agents in dissolving the food are certain ferments v/hich are found in the digestive juices, the saliva of the mouth, the gastric juice of the stomach, and the pancreatic juice of the small intestine. We shall deal with these digestive juices in order, and with the foods they act upon. We have already said that the food, whilst being chewed in the mouth, is mixed with saliva, which, as well as being a digestive juice, keeps the mouth moist, and thus assists speech. It is secreted by certain glands called the salivary glands. About three and a half pints of saliva are poured into the mouth in twenty-four hours, and it is some- times increased at the sight and smell of food, when the " mouth waters." I
