Histological anatomy of the stomach and duodenum

Stomach

The gastric epithelial cells are mucous producing and are turned over rapidly. In the pyloric part of the stomach and also the duodenum mucus-secreting glands are found. Most of the specialised cells of the stomach (parietal and chief cells) are found in the gastric crypts (Fig. 51.3). The stomach is also richly endowed with endocrine cells.

Parietal cells

These are in the body (acid-secreting portion) of the stomach and line the gastric crypts, more abundant distally. These are responsible for the production of hydrogen ions to form hydrochloric acid, which has a pH of around 1. The hydrogen ions are actively pumped by the proton pump, a hydrogen—potassium APTase (Sachs) which exchanges intraluminal potassium for hydrogen ions. The potassium ions enter the lumen of the crypts passively but the hydrogen ions are pumped against an immense concentration gradient (1 000 000:1), explaining the fact that this is an energy-consuming process.

Chief cells

These lie principally proximally in the gastric crypts and produce pepsinogen. Two forms of pepsinogen are described: pepsinogen I and pepsinogen II. Both are produced by the chief cell but pepsinogen I is produced only in the stomach. The ratio between pepsinogens I and II in the serum decreases with gastric atrophy, and this has been investigated as a means of selecting patients who are at higher risk of suffering from gastric cancer for screening. Pepsinogen is activated in the stomach to produce pepsin, the active enzyme.

Endocrine cells

The stomach is richly endowed with endocrine cells, which are critical to its function. In the gastric antrum the mucosa contains G cells which produce gastrin. Throughout the body of the stomach enterochromatin-like (ECL) cells are abun­dant and produce histamine, a key factor in gastric acid secretion. In addition, there are large numbers of somatostatin-producing D cells throughout the stomach, and somatostatin has a negative regulatory role. The peptides and neuropeptides produced in the stomach are discussed later.

Duodenum

The duodenum is lined by a mucus-secreting columnar epithelium. In addition, Brunner’s glands lie beneath the mucosa and are similar to the pyloric glands in the pyloric part of the stomach. Endocrine cells in duodenum produce cholecystokinin and secretin.