Melanocytic Lesions Basicmedical Key Melanocytic Lesions and Disorders of Pigmentation Obgyn Key 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, Comparison of melanosomes distribution in dark and light skin. Pigmentation mechanism in different phototypes. Close up of epidermis cross section. Infographic medical diagram. Vector illustration. Stock vektor Adobe Stock