Under the microscope, the stomach has three main layers. The surface layer is called the mucosa, which contains the glands that secrete the stomach acid and enzymes. Beneath this is the submucosa. Underneath this there is a large muscle layer called the muscularis externa, which is essential to churn and break up the food.

When the stomach is inflamed over a long period, this can result in the formation of a stomach ulcer. This may happen due to either direct damage to the stomach lining hindering it ability to protect itself from the stomach acid, or through there being just too much acid for the defences to cope.