Compare and contrast hematemesis, hematochezia, and melena. Explain how the color gives the investigator clues as to the location of the bleed. Why would a rapid GI transit time produce hematochezia?

What will be an ideal response?

hematemesis: vomiting blood
hematochezia: red blood in the stool
melena: black, tarry stools due to blood that has been exposed to GI secretions

Blood is broken down as it passes through the intestinal tract and changes color as it progresses through the breakdown process. Blood goes from red, to dark brown, and then to black. Bright red blood in the stool typically originates from the anus or rectum and possibly from the colon. Long exposures to gastrointestinal secretions turn the blood black with a tarry consistency. Black, tarry stools indicate the blood has originated higher up in the GI tract and traveled a significant distance. An upper GI bleed normally produces melena, but a rapid transit time would reduce the blood's exposure to GI secretions and may cause the blood to be passed mostly intact, appearing as red blood (hematochezia).