Anatomy of the Stomach
The stomach (figure 16.10) is an enlarged segment of the digestive tract in the left superior part of the abdomen. The opening from the esophagus into the stomach is called the gastroesophageal opening. The region of the stomach around the gastroesophageal opening is called the cardiac region because it is near the heart. The most supe-rior part of the stomach is the fundus (fŭn′ dŭs). The largest part of the stomach is the body, which turns to the right, forming a greatercurvature on the left and a lesser curvature on the right. The open-ing from the stomach into the small intestine is the pyloric (pı̄-lōr′ ik; gatekeeper) opening, which is surrounded by a relatively thick ring of smooth muscle called the pyloric sphincter. The region of the stomach near the pyloric opening is the pyloric region.
The muscular layer of the stomach is different from other regions of the digestive tract in that it consists of three layers: an outer longitudinal layer, a middle circular layer, and an inner oblique layer. These muscular layers produce a churning action in the stom-ach, important in the digestive process. The submucosa and mucosa of the stomach are thrown into large folds called rugae (roo′ gē; wrinkles) (figure 16.10a) when the stomach is empty. These folds allow the mucosa and submucosa to stretch, and the folds disappear as the stomach is filled.
The stomach is lined with simple columnar epithelium. The mucosal surface forms numerous tubelike gastric pits (fig-ure 16.10b), which are the openings for the gastric glands. The epithelial cells of the stomach can be divided into five groups. The first group consists of surface mucous cells on the inner surface of the stomach and lining the gastric pits. Those cells produce mucus, which coats and protects the stomach lining. The remaining four cell types are in the gastric glands. They are
1. mucous neck cells, which produce mucus;
2. parietal cells, which produce hydrochloric acid andintrinsic factor;
3. endocrine cells, which produce regulatory chemicals; and
4. chief cells, which produce pepsinogen (pep-sin′ō-jen), aprecursor of the protein-digesting enzyme pepsin (pep′ sin; pepsis,digestion).
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