The stomach is usually considered the continuation of the esophagus; although it is the following portion of the digestive tract, structurally, it has great differences. The stomach is similar to a J-shaped elastic bag, located under the ribs, in the superior part of the abdominal cavity, on the left side of the liver. It is a hollow organ that has the incredible ability to increase up to 20 times its original size in order to momentarily house and process the food bolus. It is made up of different portions. This way, its superior part, in direct connection with the esophagus, is referred to as cardia. Next we find the fundus (where the gases accumulate), the body (portion with the greatest surface), lower we find the antrus (stretching zone) and finally, the pylorus (which joins the end of the stomach with the beginning of the small intestine). The stomach connects to the esophagus through the inferior esophageal sphincter; it acts as a true passage valve, that opens or closes the junction between the two structures in order for the food bolus to not go back. The same safety mechanism is found in the final portion of the stomach, in the connection with the first part of the small intestine (duodenum).
Here, the passage valve is called pyloric sphincter.The stomach has great anatomic flexibility and it is due to it being made up of several muscle layers (oblique, longitudinal and circular) that spring into action during digestion, easing the contraction and relaxation of its walls in order to process the food bolus, just like a blender.
The inside of the stomach houses corrosive (that wear out) fluids called gastric juices. For this reason, besides counting with important muscles, it has several layers.
The serosa (smooth membrane that secretes serum) is the sheet that covers the outside of the stomach, while the mucosa is the innermost layer, which contains an important number of gastric glands (manufacturers of gastric juice).In the stomach, without a doubt, important transformations take place; however, at this portion of the digestive tube, food has not been absorbed yet. This process only just begins in the sinuous road made up of the two intestines, small and large.
