GASTROINTESTINAL HEMORRHAGE (2): Melena. Melena, the passage of black, tarry stools, usually implies blood loss greater than 500 ml originating anywhere between the oropharynx and the right hemicolon. Melena occurs most often, Macroscopic appearance of opened ileal and colonic segments and stool Download Scientific Diagram The Scoop On Poop Access Health Care Physicians Hematochezia vs. melena: What's the difference? UT MD Anderson What is the difference between tarry stools and black stools in terms of gastrointestinal (GI) bleeding?