Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) ulcerative colitis ?
    ### Response:
    Ulcerative colitis is a chronic disorder that affects the digestive system. This condition is characterized by abnormal inflammation of the inner surface of the rectum and colon, which make up most of the length of the large intestine. The inflammation usually causes open sores (ulcers) to develop in the large intestine.
    