8 Stomach
Stomach overview:
After exiting the esophagus food enters the stomach, a J-shaped organ which lies between the esophagus and the entry of the small intestine. It spans the epigastric and left hypochondriac regions.
The stomach receives the food bolus from the esophagus which enters through the LES and acts like a blender, grinding down ingredients into a smaller, more fluid liquid called chyme.
The stomach has several identifiable features, containing several folds of the mucosa layer, called rugae. Further, the stomach can be divided into 5 areas:
Table 8 Structural components of the stomach
| Component | Description: |
| Cardia | The top section, located closest to the heart |
| Fundus | The rounded section, located under the diaphragm |
| Body | The largest section, located just below the fundus |
| Antrum | An intermediate section, located beneath the body |
| Pylorus | The bottom and most distal part of the stomach, which contains the pyloric sphincter |
Figure 9 Anterior view of the stomach and its regions
Stomach Digestion:
The stomach’s main job is to break down food through two ways: mechanically, through involuntary muscular contraction and chemically through enzymes and acids.
Mechanically, the stomach breaks down food through rhythmic contractions known as peristaltic contractions – similar to that seen in the esophagus. The stomach’s smooth musculature aids in this rhythmic contraction to churn food into chyme:
Figure 10 Peristaltic contractions of the stomach
Chemically, the stomach produces various secretions from several types of cells to aid in digestion:
Table 9 Cells of the stomach
| Cell name | Description: |
| Parietal cells | produce gastric acid (including hydrochloric acid or HCL) to break down organic matter |
| G-cells | produce gastrin to stimulate acid secretion in the stomach |
| Chief cells | produce pepsinogen to break down proteins, and gastric lipase to break down fats |
| Goblet cells | produce mucus, acting like a protective raincoat to shield the stomach lining from the acid |
Figure 11 Anterior view of the stomach’s cells
Note how there are no enzymes specific to breaking down carbohydrates present in the stomach – this is facilitated through the mouth and small intestine.
The cells of the stomach are very important!
Hint: Another often overlooked aspect of the digestive system are the roles of parietal, chief, and goblet cells which play key roles in digestion within the stomach. Don’t forget to review these cells and their functions with respect to digestion.