How is food processed in the stomach?

Food is processed in the stomach through mechanical and chemical digestion involving enzymes and stomach acid.

In the stomach, food undergoes both mechanical and chemical digestion. The process begins when food enters the stomach from the oesophagus, a process controlled by a ring of muscles called the lower oesophageal sphincter. The stomach, a muscular bag, then uses peristalsis - rhythmic contractions - to churn and mix the food, breaking it down into smaller pieces. This is the mechanical aspect of digestion.

Chemical digestion in the stomach involves the secretion of gastric juices, which contain hydrochloric acid and enzymes. The hydrochloric acid creates an acidic environment, with a pH of around 2, which is necessary for the activation of the enzyme pepsin. Pepsin is a protease enzyme, meaning it breaks down proteins into smaller peptides. The stomach lining also secretes a mucus that protects it from being digested by the acid and enzymes.

The combination of mechanical and chemical digestion in the stomach transforms the food into a semi-liquid substance called chyme. Once the chyme is adequately broken down, it is gradually released into the small intestine for further digestion and absorption.

The stomach also has a role in killing bacteria in the food we eat, with the acidic environment helping to neutralise potentially harmful microorganisms. This is an important part of the body's defence system against infection.

In summary, the stomach processes food through a combination of mechanical churning and chemical digestion involving hydrochloric acid and enzymes. This results in the breakdown of food into a form that can be further digested and absorbed in the small intestine.