An ulcer is a type of injury where all of the cells that are normally found on the surface of a tissue are damaged or lost and the tissue below the surface is exposed.
The cells on the surface of a tissue are called epithelial cells and they form a barrier called the epithelium. The tissue below the epithelium is called stroma. The epithelium protects the stroma from the environment both inside and outside of the body.
There are many kinds of epithelium in the body and some have special names. For example, the surface of the skin is covered by an epithelium called the epidermis.
An ulcer forms when the epithelial cells are damaged and the stroma is left uncovered.
An ulcer can be caused by trauma, infection, and inflammation. Tumours can also cause an ulcer as the cancer cells damage the surrounding normal tissue.
Common sites for ulcers include the skin, stomach, and oral cavity although they can develop anywhere in the body.
An ulcer is a descriptive term and other information is usually required to determine the cause for the ulcer.