Stomach

About the Stomach

The stomach is a J shaped muscular organ between the esophagus and duodenum, with four regions cardia, fundus, body, and pylorus. It holds approximately 1 to 1.5 liters after a meal. The stomach lining has rugae folds that expand with filling. Gastric glands contain parietal cells secreting hydrochloric acid pH 1.5 to 3.5 and intrinsic factor essential for B12 absorption, chief cells secreting pepsinogen activated to pepsin by acid for protein digestion, G cells secreting gastrin stimulating acid production, and mucous cells protecting the lining from acid damage through mucus and bicarbonate barrier. The muscularis externa has three layers inner oblique, middle circular forming the pyloric sphincter, and outer longitudinal, providing strong churning and mixing peristalsis. The stomach converts food into chyme, a semi liquid mixture released gradually into the duodenum through the pyloric sphincter. The cephalic phase 30 percent of secretion begins with the thought, sight, or smell of food via the vagus nerve. The gastric phase 60 percent is triggered by food distension and peptides. The intestinal phase 10 percent involves hormonal feedback from the duodenum.