Which disease is characterized by blood diarrhea and primarily affects the colon?

Ulcerative Colitis is characterized by blood diarrhea and primarily affects the colon. This chronic inflammatory bowel disease causes inflammation and ulceration of the colonic mucosa. Patients often present with symptoms such as bloody and mucoid diarrhea, abdominal pain, and urgency to defecate. The inflammation is typically continuous, starting from the rectum and extending proximally, which distinguishes it from other gastrointestinal diseases.

While Crohn's Disease can also result in diarrhea and affects the gastrointestinal tract, it can occur anywhere from the mouth to the anus, and blood in the stool is less common in comparison to Ulcerative Colitis. Colorectal cancer could present with bloody diarrhea, but it does not exclusively cause diarrhea as a primary symptom and often involves other systemic signs of malignancy. Gastroenteritis typically causes watery diarrhea rather than bloody diarrhea, and is more commonly associated with infectious agents rather than chronic inflammation or structural changes in the colon.

Thus, Ulcerative Colitis stands out as the condition that specifically features blood in the diarrhea and predominantly involves the colonic region.