The feeling of distension in the abdomen under the umbilicus and discomfort at the anal opening are mainly the symptoms of acute and severe pain, which can be seen in dysentery, ulcerative colitis, colorectal cancer and other diseases. 1. Dysentery: including bacillary dysentery and amoebic dysentery, respectively, caused by bacterial infection and amoebic protozoan infection, the main clinical manifestations are diarrhea, acute and severe symptoms. The main clinical manifestations are diarrhea, acute and severe symptoms, etc. It is necessary to replenish fluids in time, pay attention to rest, and use antibiotics such as penicillin for treatment. 2. Ulcerative colitis: a kind of inflammatory bowel disease, its main manifestation is diarrhea, mucus, pus and blood stools, accompanied by acute and severe. The main treatment method is medication, such as salazosulfapyridine and other drugs can be used. 3. Colorectal cancer: It is the cancer that occurs in colorectum, which may manifest diarrhea, abdominal pain, constipation, blood in stool and so on. The main treatment method is surgery, supplemented by postoperative radiotherapy. If there is distension in the abdomen under the umbilicus and discomfort in the anal opening, one should consult a doctor in time to receive professional examination and treatment, so as to avoid delaying the condition.