Inflammation has cell and fluid components. The cell component includes various white blood cells. The type of white blood cells found in the lining of the intestine determines the cause and effect on the intestine. Fluids include chemicals secreted to fight infection or presumed infection not present that can cause damage to the colon lining.

Typically gastrointestinal inflammation is characterized visually by redness and swelling of the lining surface known as the mucosa. If the inflammation has resulted in more significant injury to the surface lining then breaks in the mucosa results giving rise to either superficial erosions or larger, deeper ulcerations. Inflammation can result in swelling of the lining or constriction of the lumen or diameter of the GI tract resulting in obstruction.

Under the microscope the lining of the gastrointestinal tract that is inflamed will show signs of infiltration of various types of white blood cells or inflammatory cells depending on the nature or cause and how recent (acute) or chronic the inflammation. Damage to the lining cells, particularly the cells that produce mucus, digestive enzymes, and absorb nutrients, vitamins and water can be seen under the microscope depending the cause, duration and the severity of the inflammation.

Small superficial mucosal breaks are called erosions. Larger and deeper breaks are termed ulcers. Ulcers typically look like canker sores seen in the mouth. Both erosions and ulcers can bleed and can occur anywhere throughout the gastrointestinal tract.

Classic symptoms of gastrointestinal inflammation are pain, digestion and absorption difficulties usually resulting in bloating and altered bowel patterns, especially diarrhea. Obstruction of the gastrointestinal tract can occur from scarring resulting from inflammation and healing. Bleeding can occur from damage to the lining of the gastrointestinal tract. The character of bleeding depends on the location of the bleeding site and the amount and rate of bleeding.