The stomach is a bean-shaped organ located in the digestive tract, or alimentary canal. Hollow and muscular, the stomach plays an important role in the second stage of digestion. Highly acidic in nature, the stomach, which lies between the esophagus and the small intestine, contains a variety of digestive enzymes. This allows the organ to break down food into smaller, chemical components which the body can absorb in the intestines and send out to the cells that need the nutrients.
The stomach has five layers. The innermost layer, or mucosa, generates gastric acid, the main secretion of the stomach which has a pH level of 1-2 which makes it easier for the organ to break down proteins in food. The submucosa is next. This level contains loose connective tissue which supports the mucosa. It also connects the mucosa to the underlying smooth muscle tissues. The blood and lymphatic vessels and nerves, which supply the mucosa with all that it needs to survive, also pass through this portion of the organ.
The muscularis externa makes up the next layer of the human stomach. Composed of muscle tissue, the muscularis is responsible for peristalsis, a rhythmic contraction which propels the contents of the stomach to other parts of the digestive tract, most notably the duodenum, the opening of the small intestine. The serosa follows the muscularis externa. A smooth membrane consisting of a thin cellular layer, it secretes something called serous fluid. Serous fluid, which is usually pale, transparent and yellow, acts as a lubricant. It also contains enzymes such as amylase which helps the body digest carbohydrates. Finally, the subserosa is a layer of tissue that supports the serosa. It forms the outer lining of the stomach and acts as a buffer between the organ and the rest of the body.