The stomach and duodenum are very important parts of the gastrointestinal system. The cardiac valve at the lower end of the oesophagus leads into the stomach, a dilated part of the bowel, which leads into the duodenum via the pyloric valve. The relatively short duodenum in turn proceeds into the start of the very lengthy small bowel.
The stomach is important, for here digestion really commences. Powerful glands in the wall of the stomach pour forth a variety of fluids that act forcibly on the food as soon as it enters. Under the powerful dissecting microscope, the stomach lining has the appearance of a lattice caused by the opening of myriads of gastric glands. Near the cardiac valve, these glands produce chiefly mucus, a thick, heavy fluid, rather jellylike in nature. (This material is often seen in vomitus.)
The greater part of the stomach walls contain glands that actively secrete hydrochloric acid, pepsinogen and other chemicals. These all play a part in food digestion. Toward the far end of the stomach, the glands produce a powerful chemical called gastrin. The presence of food activates the production of gastrin, which in turn causes the other glands to secrete their gastric juices, and so aid digestion. Controlled by Nervous System But apart from this, most of the glands are under the direct action of the nervous system (the computer like mechanism we talked of earlier). This may also regulate gastric-juice production.
Most people are aware of the effect that mental tensions, anxieties and stresses have upon the stomach. Acting through the nervous system, potent gastric juices (containing all the components mentioned) may be liberated in force.
This is probably one reason why such a high incidence of ulcers attaches to occupations in which stress and mental turmoil are an everyday accompaniment. The stomach and duodenum are sites for some very important pathological processes. Peptic ulcers (that means a break in the mucosal lining) are very common, particularly in the duodenum.
Also, the stomach, being the place where all food and fluid intake must go as the first port of call, is subjected to all manner of abuses. Therefore, dietetic indiscretions (foolish food items, excesses of alcohol and other irritants, acid from cigarette smoking) frequently play a major part in producing adverse symptoms. Not only may they help to cause ulcers, but general inflammation of the lining walls (gastritis) can readily take place.
Infections also may gain entry into the intestinal system through this route. One of the system’s most lethal forms of cancer, carcinoma of the stomach, occurs here. Unfortunately, as with oesophageal cancer, symptoms appear usually when it is too late to provide an effective cure.