1. ELECTRICAL PHENOMENA IN THE HUMAN STOMACH.
1.1. THE ANATOMY OF THE STOMACH.
The main function of the stomach is to process and transport food. After feeding, the contractile activity of the stomach helps to mix, grind and eventually evacuate small portions of chyme into the small bowel (12), while the rest of the chyme is mixed and ground.
Anatomically, the stomach can be divided into three major regions: fundus (the most proximal), corpus and antrum (Fig.1.1). Histologically, the fundus and corpus are hardly separable. In the antral area, the density of the smooth muscle cells increases (11).
Figure 1.1. Macroscopic anatomy of the stomach.
The stomach wall , like the wall of most other parts of the digestive canal, consists of three layers: the mucosal (the innermost), the muscularis and the serosal (the outermost). The mucosal layer itself can be divided into three layers: the mucosa (the epithelial lining of the gastric cavity), the muscularis mucosae (low density smooth muscle cells) and the submucosal layer (consisting of connective tissue interlaced with plexi of the enteric nervous system). The second gastric layer, the muscularis, can also be divided into three layers: the longitudinal (the most superficial), the circular and the oblique (Fig.1.2). The longitudinal layer of the muscularis can be separated into two different categories: a longitudinal layer that is common with the esophagus and ends in the corpus, and a longitudinal layer that originates in the corpus and spreads into the duodenum.
Figure 1.2. Structure of Gastric Muscularis: A -- the longitudinal layer (the area where the longitudinal fibers split is marked with a black circle); B - the circular layer; C - the oblique layer.
The area in the corpus around the greater curvature, where the split of the longitudinal layers takes place, is considered to be anatomically correlated with the origin of gastric electrical activity (11). The circular layer of the muscularis is continuous with the circular layer of the esophagus, but is absent in the fundus (12). The thickness of the circular layer increases in the antrum and especially in the pyloric sphincter (9). It does not continue into the duodenum. The oblique layer of the muscularis is clearly seen in the fundus and near the lesser curvature of the corpus, but the oblique fibers disappear distally (towards the antrum). The outermost main layer is the serosa (Fig. 1.3).
Figure 1.3. Cross section of gastric wall. Nerve plexi provide the interface between the mucosa and the muscularis, as well as between the longitudinal and circular layers of the muscularis (9, 12).