The human stomach is located on the upper left region of the abdominal cavity, and is a vital part of the digestive system. It lies just beneath the diaphragm, and is muscular and hollow in nature. If you take a look at the alimentary canal, stomach is preceded by the esophagus, and followed by the duodenum.
In other words, this part of the digestive system is located between esophagus and duodenum. The esophageal sphincter controls the movement of food from the esophagus to the stomach, and the pyloric sphincter is responsible for regulating the motion of partially digested food from the stomach to the duodenum, which is the first part of the small intestine.
It is a sac-like structure with an empty volume of around 45 to 75 ml (in humans). However, in normal adult humans, it can get enlarged, and hold 1 to 3 liters of food and liquids. This is not applicable for babies, who can hold only 30 ml in their stomach.
In short, the size of the stomach alters as per the amount of food consumed. In an average adult, the stomach has a length of around 10 to 12 inches.
Parts of the Stomach
The stomach has four parts, which are named cardia, fundus, corpus (body), antrum, and pylorus. While cardia is the first part of the stomach, which receives food from the esophagus; fundus is that section of the stomach, that is formed by the greater curvature.
The body or corpus forms the main central region of the organ; and the antrum, along with the pylorus, forms the last part that empties the contents of the stomach to the duodenum.
Muscularis externa consists of three layers of muscles, that are responsible for mixing the food with enzymes and the movement of the food. So, this layer has an important role in the function of the stomach. The outermost layer is serosa, which is made of connective tissues.
The inner surface of the stomach has different types of epithelial cells that produce various secretions which aid the process of digestion. They include mucus cells that produce mucus, which is alkaline in nature. This mucus prevents harm to the inner layer of the stomach from acids.
There are chief cells that produce an enzyme called pepsin (aids in breaking down proteins), and parietal cells that produce hydrochloric acid (fights microorganisms and digests food). Another type of epithelial cells in the stomach are G cells that produce a hormone called gastrin.
The inner surface of the stomach has several foldings, called rugae, which flatten as the stomach expands.
What is the Function of the Stomach?
The function of the stomach implies the co-ordinated efforts of various parts of the organ. We all know that the primary function of the stomach is collection and breaking down of food. The food we eat is chewed in the mouth, and it is said that the process of digestion starts in mouth. What happens in the stomach can be considered second phase of digestion.
The chewed food reaches the stomach, and gets mixed with the acids and enzymes produced in the organ. This mixture is called chyme, which is stored in the stomach; and is released to the small intestine in small amounts. Thereafter, it is the small intestine's function to break down the chyme further, and absorb the nutrients.
So, the primary function of the stomach is breaking down of the food, and mixing it with digestive acids and enzymes. Apart from that, the secretions of the stomach kills harmful microorganisms, like bacteria.
In short, the stomach's function is to aid digestion by breaking down the food and mixing it with acids and enzymes, thereby releasing the resultant chyme to the small intestine.