Oral Melanotic Macule: Symptoms and Treatment Skinsight 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, Recognition of Melanocytes in Immuno Neuroendocrinology and Circadian Rhythms: Beyond the Conventional Melanin Synthesis Differentiating between early melanomas and melanocytic nevi: A state of the art review ScienceDirect