The stomach is a hollow muscular organ in the gastrointestinal tract of humans. It is situated between esophagus and duodenum, inferior to the diaphragm in the left part of the abdominal cavity. The stomach is a roughly crescent-shaped enlargement of the gastrointestinal tract. The stomach has the ability to expand or contract as the inner of it is rich of wrinkles (also called rugae). The structure of stomach typically divided into four regions that are cardia, the body of stomach, fundus and pyloric. And like the other gastrointestinal tract, stomach tissue is made up of four distinct layers: the mucosa, submucosa, muscularis, and serosa layers. The main functions of the stomach are to store the food we eat and secrete a mixture of digestive enzymes, mucus as well as gastric acid that help to digest and sanitize the food. In addition, the stomach performs the absorption of iron and highly fat-soluble substances like alcohol and some drugs. Conditions associated with stomach include gastritis, peptic ulcer, and cancer. A variety of target molecules expressed on stomach tissue are used in the detection of related diseases.