The stomach is a J-shaped dilation of the alimentary tract bounded proximally the lower esophageal and distally by the sphincter.
stomach is divided into four regions. The cardia is a poorly defined transition from the esophagogastric junction to the fundus. The fundus projects up above the cardia and is continuous with the body pus), which is characterized by longitudinal folds known as rugae.
The antrum is the distalmost part of the stomach commencing at the incisura angularis and continuing on to the pylorus, a circular muscle region joining the stomach to the duodenum. The stomach is lined by a mucosa of columnar cells underneath which is a submucosa of connective tissue. Beneath that are inner oblique, middle circular, and outer longitudinal smooth muscle layers that are covered by serosa. The anterior and posterior trunks of the vagus nerve provide parasympathetic innervation, whereas sympathetic nerves originating from the celiac ganglia travel in concert with blood vessels supplying the stomach. The stomach is characterized microscopically by mucus-containing columnar surface cells and invaginated pits for gastric glands that vary in the different regions of the stomach. The oxyntic, or acid-producing, region of the stomach is found in the fundus and body, where gastric glands contain characteristic parietal cells, which secrete both acid and intrinsic factor. These glands also contain zymogen-rich chief cells, which synthesize pepsinogen, and enterochromaffin-like endocrine cel which secrete histamine. Antral glands have different endocrine cells: gastrin-secreting G cells and somatostatin-secreting D cells, which are often in close proximity to the G cells. The duodenum, the first part of the small intestine, forms a C-shaped loop around the head of the pancreas and is bounded by the pylorus proximally and the jejunum distally. The first part of the duodenum is the duodenal bulb, which is characterized by a featureless surface, whereas the remainder of the duodenum has characteristic circular folds that increase the surface area available for digestion.
The duodenum is divided into a mucosa, submucosa, muscularis and serosa much like the stomach and is innervated in a similar fashion.
The mucosa consists of columnar cells with a villiform appearance, underneath which are submucosal Brunner’s glands that secrete bicarbonate-rich secretions needed to commence the neutralization of gastric acid.