The stomach is the dilated portion of the alimentary canal and has following main functions:
- It stores food (in the adult it has a capacity of about 1500 mL),
- It mixes the food with gastric secretions to form a semifluid chyme, and it controls the rate of delivery of the chyme to the small intestine so that efficient digestion and absorption can take place.
The stomach is situated in the upper part of the abdomen, extending from beneath the left costal margin region into the epigastric and umbilical regions. Much of the stomach lies under cover of the lower ribs. It is roughly J-shaped and has two openings, the cardiac and pyloric orifices; two curvatures, the greater and lesser curvatures; and two surfaces, an anterior and a posterior surface.
The stomach is relatively fixed at both ends but is very mobile in between. It tends to be high and transversely arranged in the short, obese person (steer-horn stomach) and elongated vertically in the tall, thin person (J-shaped stomach). Its shape undergoes considerable variation in the same person and depends on the volume of its contents, the position of the body, and the phase of respiration.