Stomach is part of the digestive system and receives food from the esophagus. A bottle shaped organ in humans. It is normally less than 20 cm (18 in) long and weighs about 1 percent of the body weight. It is capable, however, of distending greatly to accommodate large meals without increasing the pressure to tension on its walls.

The stomach secretes large amounts of hydrochloric acid, which digests protein, activates pepsinogen to form the enzyme pepsin, and kills bacteria that enter the stomach. Acid is secreted from the oxyntic gland area of the gastric mucosa; other cells in this area secrete mucus and the proenzyme pepsinogen. Mucosa lubricates and protects the stomach wall and prevents acid from digesting the stomach itself. Pepsin is an enzyme that aids in the digestion of protein.

The mucosa of the distal third of the stomach (antrum) produces and releases the hormone gastrin into the bloodstream), which stimulates acid secretion and the growth of mucosa in the digestive tract. The sight of food and its presence within the mouth activate the vagus nerve, which dirrectly stimulate the parietal cells to secrete acid, and the antral gastrin cells, which release gastrin into the bloodstream. The vagus nerve also stimulates pepsinogen and mucus secretion. Distention of the stomach and protein digestion products also stimulate both the parietal cells and the release of gastrin.

In abnormal conditions, the secretion of acid and pepsin is ultimately responsible for peptic ulcer disease characterized by painful lession in the gastric wall. Medical treatment of peptic ulcer disease is directed either at inhibiting acid secretion or at neutralizing secreted acid by the use of antacids.


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