A Master Guide to Understanding & Caring For Your Melanin Rich Skin Melanin Definition, Types & Function Lesson Study.com 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, Melanocyte differentiation and mechanosensation are differentially modulated by distinct extracellular matrix proteins EMBO Reports Springer Nature Link