a. The stomach is a musculomembranous, J-shaped enlargement of the
alimentary canal and is located between the esophagus and the duodenum. See figure
1-1 for the position of the stomach. The stomach is divided into three parts: the fundus,
the body, and the pylorus. The fundus is the upper rounded portion of the stomach
located above and to the left of the cardia. The body of the stomach is the large central
portion which is located below the fundus. The pylorus is the narrow, inferior region of
the stomach. In every person, the position and size of the stomach vary continually.
For example, the diaphragm pushes the stomach down each time a person breathes in
and pulls the stomach up each time a person breathes out. When the stomach is
empty, it is about the size of a large sausage, but when an individual eats a large
amount of food, the stomach stretches as necessary and may become very large.
Figure 1-3. Stomach.
b. The cardiac sphincter muscle guards the opening between the esophagus
and the stomach. The pyloric sphincter muscle guards the opening between the
stomach and the small intestine. The stomach contains glands called gastri pits which
are lined with secreting cells. The zymogenic cells (the chief cells) secrete the
substance pepsinogen. During the digestive process, pepsinogen comes in contact
with hydrochloric acid (produced by the stomach parietal cells) creating the principal
gastric enzyme pepsin.
The cardiac sphincter cannot perform its functions when an individual is