When having a discussion concerning anatomy the phrase form determines function comes to mind. What this entails is that the structure of the organ determines strongly what that organ does. The stomach is a muscular sac that provides a conducive enviroment for breaking down, chemically modifying, and sending to the next stage of digestion the food or material that a human or any other mammal for that matter eats.
The stomach is an expanded section of the gastrointestinal tract between the esophagus and the duodenum of the small intestine. The stomach is on the left side of theabdominal cavity with the most superior part laying against the diaphragm . Inferior to the stomach is the pancreas and the greater omentum which hangs from the greater curvature. The major regions of the stomach are thecardia, fundus, body, antrum, and the pylorus. Additionally you have the greater and lesser curvatures, which are the right and left sides of the stomach, respectively. The esophageal sphincter is contained within the carida region. The esophageal sphincter controls the flow of material coming into the stomach. The fundus is the section of the stomach that is formed by the upper curvature and the body is the main area of the stomach. The final part of the stomach is the antrum where the pylorus, the exit of the stomach and entrance to the duodenum of the small intestine is located. Within the pylorus is the pyloric sphincter that controls what leaves the stomach into the duodenum.
The inside of the stomach is composed of three layers, from the innermost layer to the outermost layer: muscosa, submuscosa, muscularis externa, and the serosa. The muscosa is where stomach acid is produced and secreted into the stomach. The submuscosa is layer composed of connective tissue that separates the muscosa from the muscularis externa. The muscularis externa is composed of three layers of smooth muscle: inner oblique, middle circular, and outer longitudinal. These are the muscles that are primarily responsible for mixing material that has come into stomach with digestive enzymes and moving the material through the stomach. The final layer is the serosa, which is a layer of connective tissue that attaches and is continuous with the peritoneum, the lining of the abdominal cavity.
The primary functions of the stomach are killing bacteria and breaking down food releasing to the small intestine while maintaining a constant release rate of material from the stomach to the small intestine. The pH inside of the stomach is maintained at very acidic levels which help the digestive enzymes like pepsin break down the material further so it can be moved to the small intestine successfully. Finally, the stomach is also responsible for helping the small intestine absorb vitamins.