The stomach is a sack like muscular organ located in the upper-left side of the abdomen just below the liver. The primary function of the stomach is to hold and breakdown food and liquid that we consume in our meals. It secretes hydrochloric acid and enzymes that help in the breakdown of food and other foreign particles like bacterial pathogens. This acid secretion can cause stomach ulcer, but the acid does not burn the stomach as there is slimy mucus which protects the stomach lining from the attack of acid that is used in the digestion of food. This acidic medium in the stomach also kills the unwanted Bacteria. The stomach structure is such that the stomach muscles contract at regular intervals to churn the food and enhance the digestion process. About 40 minutes to a few hours is taken by the stomach to break down the food.
An average stomach can hold up to 1 liter of food comfortably. But the holding capacity of the stomach can be expanded to a maximum of 4 liters due to its elastic nature. This is the reason our stomach expands when it is full and becomes normal when the food gets digested. If consistently we keep on eating more than 1.5 liters of food then our stomach will stretch itself to a capacity of 1.5 liters.
Our brain gives a signal when our stomach is full. But the brain does not respond immediately after the stomach is full. It can be the possibility that we overeat sometimes. This is the reason we should eat food slowly. By eating slowly, we chew our food properly so that the process of digestion occurs smoothly. The major role of the stomach in digestion is to churn the food properly coming from the esophagus so that small intestine can absorb the molecules. In the stomach, food and water are mixed properly to form a slurry known as chyme. After this process, the food is ready to move into the small intestine. The liver, gall bladder, and pancreas are known as the alimentary system of humans and together help in the process of digestion.
This was just a brief layout of the digestion process and how stomach helps in the process of digestion. To visualize digestion processes watch the video.