Stomach Health Article

Exocrine secretions

Exocrine glands are located in the fundus and body of the stomach. The chief cells in these exocrine glands secrete pepsinogen, the inactive precursor of pepsin. Pepsin is an enzyme that is responsible for the initial breakdown of protein molecules into smaller polypeptides. If pepsin did not have an inactive form, it would destroy the chief cells as they produced it. Pepsin can be activated in the stomach, because the stomach lining is protected from its action.

The exocrine glands of the fundus and body of the stomach also contain parietal cells. These parietal cells secrete hydrochloric acid (HCl), which makes the stomach strongly acidic, with a pH of about 2 or 3. This is an optimal pH for the action of pepsin. Hydrochloric acid is responsible for transforming the inactive pepsinogen into active pepsin. The hydrochloric acid in the chyme also stimulates the production of pancreatic and biliary secretions that further stimulate digestion. The acidic environment kills most bacteria that enter the digestive tract through the mouth. Parietal cells also release a chemical called the intrinsic factor, which is necessary for the absorption of vitamin B₁₂.

Mucous cells release an alkaline mucous fluid into the gastric wall, protecting it against the damaging action of stomach acid. The fluid neutralizes the hydrochloric acid and also acts as a lubricant, protecting the inner lining of the stomach.

Endocrine secretions

The G-cells are the only endocrine cells located in the stomach and are located mainly in the antrum of the stomach where there are few acid producing cells. G-cells release the hormone gastrin into the bloodstream. Gastrin acts on the parietal cells, stimulating them to release hydrochloric acid.

Muscular activity

The stomach must undergo muscular contractions in order to mix food and gastric juices together. These waves of involuntary muscular contractions are called peristalsis. When food is present, peristaltic contractions pass through the stomach muscles about two or three times every minute and continue at a constant rhythm. Pressure will begin to develop in the lower part of the stomach. When there is sufficient pressure, a small amount of the stomach's contents moves through the pyloric sphincter and into the duodenum (the first section of the small intestine). It takes about two to six hours for the entire contents of the stomach to empty, depending on the composition of the person's diet. Low-fat meals leave the stomach more quickly than high-fat meals. Psychological states also affect the rate of stomach emptying; depression and fear may cause the stomach to empty slowly, while anger and aggression may cause the stomach to empty quickly.

After the chyme has entered the duodenum and the pyloric sphincter has closed, some of the food returns to the stomach through retropulsion. Retropulsion is a process in which the stomach contents are squirted back into the stomach at a rate of about three times per minute. Retropulsion mixes the food with gastric juices and breaks larger clumps of food into smaller pieces.

Role in human health

The stomach prepares food for digestion in the small intestine. If the stomach is not functioning properly, there are many problems that can arise with regard to digestion. Further, the contents of the stomach are so acidic and caustic to other organs of the body that they can cause problems if they leak out of the stomach, as may happen with perforating ulcers of the duodenum or penetrating wounds of the abdomen.

Gastritis

Gastritis is a common health problem. It is an inflammation of the gastric mucosal layer caused by a range of factors, including bacterial infections, medications (particularly NSAIDs), acute stress, and spicy foods or alcohol. Gastritis can result in a lowered functioning of chief cells and parietal cells. Less pepsin is provided to the stomach, resulting in incomplete breakdown of proteins. There is also less stomach acid secretion, allowing overgrowth of microbial populations and a decrease in the absorption of vitamin B₁₂. Gastritis can occur at any age, but chronic gastritis is frequently seen in the elderly.

Gastroenteritis

Gastroenteritis is another common disorder of the digestive tract, characterized by inflammation of the stomach and the intestines. It is the most common cause of mortality in underdeveloped nations, and in the United States it ranks second to the common cold as a cause of lost work time. Gastroenteritis is caused by specific bacteria (Staphylococcus aureus, Escherichia coli, etc.), amebae or other parasites. The symptoms of gastroenteritis include diarrhea, nausea, vomiting, and abdominal cramping. Patients can become dehydrated and malnourished if this disorder continues over an extended period of time.