Stomach
Objective 4
Indicate the location of the following stomach regions: cardiac, fundus, pylorus. Identify the sphincters of the stomach and their function: cardiac, pyloric. Describe the histology and function of the unique features of the stomach: oblique muscle layer, chief cells, parietal cells, enteroendocrine cells, and mucous cells. Explain the function, production, and regulation of hydrochloric acid (HCl).
Food and liquid leaving the esophagus pass through the lower esophageal sphincter (also called the cardiac sphincter) as they enter the stomach. The lower esophageal sphincter sometimes fails to tightly close, causing a condition called gastroesophageal reflux disease (GERD). GERD can be caused by increased abdominal pressure, as in obesity.
The stomach has five regions and two curves. The cardia is the point at which the esophagus crosses the diaphragm to become the stomach. The fundus (as in the fundus of the eye, or fundus of the uterus) comes from the same word as “foundation” of the bottle. The bulk of the stomach is the body, and the narrower part nearest the small intestine is the pylorus (Greek πσραλος, “gate-keeper”). The pyloric antrum (Latin, “cave”) transitions to the pyloric canal.
The stomach is a curved bag, and the smaller of the two curves is called, naturally enough, the lesser curvature while the larger arc is the greater curvature.
As mentioned previously, the “valve” between esophagus and stomach is the lower esophageal sphincter (cardiac sphincter). At the end of the pyloric canal is the pyloric sphincter, which represents the end of the stomach and outlet for stomach contents. The pyloric sphincter opens into the duodenum (Latin: “12 finger breadths”), which is the initial segment of the small intestine.
Like the other regions of the GI tract, the stomach follows the basic histological plan laid out in earlier. In the stomach, the mucosa layer is specialized for the digestion of food. The specialization takes the form of gastric pits. Each of these depressions is lined with a simple columnar epithelium. The bottom half of each gastric pit has a higher concentration of glandular cells that collectively are called the gastric glands.
Along the stomach lumen, epithelial cells and surface mucous cells predominate. Mucus is an essential part of the stomach lining, and protects the cells on the surface from being damaged by the acid and enzymes secreted by the stomach. Further from the luminal surface (albuminal), the gastric pit has a number of secretory (glandular) cells.
Let’s now explore the cells of the mucosa layer with more depth.
Cells of the Mucosa Layer
Mucous neck cells secrete protective mucus.
Parietal cells have two essential roles. First, they have specialized protein pumps that dump H+ and Cl– ions into the lumen, making HCl (stomach acid). More about this later. Second, they secrete intrinsic factor. Intrinsic factor is critical for absorption of vitamin B12. B12 is needed for red blood cell produc