Bowel Bleeding and Melena – Medical Terminology Meaning

Bowel bleeding and rectal bleeding which refers to the passage of blood through the anus, either in stool or on its own, are two terms that are used interchangeably. Any bleeding within the gut and specific the lower gut such as the bowels may be noticed as blood in the stool, in the toilet bowl water or even blood upon wiping after defecation. In severe cases, the bleeding is spontaneous and can even soil a patient’s underwear.

Most cases of bowel bleeding arise from the rectum and anal blood vessels in conditions like hemorrhoids. The blood is bright red and fresh which is known as hematochezia. Sometimes the blood may appear dark and old giving rise to black tarry stools which is known as melena. Bleeding should always be taken seriously although the odd episode of blood in the stool or upon wiping could be due to less serious conditions like hemorrhoids (piles).

Location of Bowel Bleeding

Melena typically indicates bleeding in the upper gut – esophagus, stomach and first parts of the small intestine. The bleeding is from the walls of the gut and due to the action of air and digestive enzymes, the blood degrades to appear black in color often with a slightly foul odor. Many people may not notice this change in the stool unless there is significant blood loss in the gut.

Hematochezia indicates bleeding in the lower gut – ileum of the small intestine, colon, rectum or anus. Often small amounts of blood in the stool is not easily noticed. In many cases bleeding is so minor that it requires special tests to identify. However, when bleeding is significant then then the blood in the stool is bright red and still fluid and therefore easily evident when wiping.

Read more on rectal bleeding.

However, there are certain instances where melena may be due to bleeding in the lower gut and hematochezia from the upper gut.

  • Constipation may slow the passage of colonic contents therefore bleeding in the colon may delay the exit. This leads to the degradation of blood and melena although it is a lower gut bleed.
  • Diarrhea causes rapid gastroesophageal motility so fresh blood from the upper gut is quickly passed out of the bowel. Therefore hematochezia in this case is from bleeding in the upper gut.

Bowel bleeding may be due to injury to the gut wall, infections, or even perforations and should always be treated as a serious sign. Although the majority of cases is due to hemorrhoids and is not serious, it is however distressing and needs to be attended to. Chronic bowel bleeding, even a light bleed, can lead to anemia. Severe acute bowel bleeding can lead to hypovolemic shock and even progress to death.

Meaning of Melena

Melena (Gk. melas = black) is a medical term for a black tarry stool due to blood in the stool, usually originating from the upper gastrointestinal tract (the stomach, esophagus, mouth, nose). It is often thought that blood in the stool due to bleeding in the gut will appear bright red and fresh but this is known as hematochezia.

However, when bleeding occurs higher up in the gut then it has to traverse the entire gut. During this time it is subjected to various digestive enzymes that breaks up the components of blood. Red blood cells are degraded and some of its components are oxidized resulting in a black color.

Sometimes blood may also be degraded when the bleeding occurs in the lower gut like within the large intestine. This is more likely to occur in people with constipation as the delay in passing out the stool results in the blood degrading within the large intestine. This is in part due to the action of bacteria in the colon.

Why does bleeding occur?

Gastrointestinal bleeding, whether in the upper or lower gut, may arise for several reasons. The wall of the gut is rich in blood vessels and the thin lining between the gut lumen and deeper tissue of the gut wall allows for blood to easily pass into the gut. Any injury or inflammation can lead to bleeding. Blood loss arises when there is a break in a blood vessel within the wall.

Read more on bleeding in the bowels.

Red to Black Blood in the Stool

Bleeding in the upper gut may occur for various reasons. Inflammation, ulcers and even tears may occur for various reasons. Less frequently, some vessels become enlarged and tortuous and are easily rupture (varices). When blood leaks into the upper gut, it has to go through the various digestive processes like food. Digestive enzymes, especially those enzymes that breakdown protein, air in the gut and the action of bowel bacteria in the lower gut systematically degrades blood. By the time it reaches the lower bowel, it has already degraded substantially.

With melena, the stool has a black tarry appearance due to large volumes of degraded blood (dark old blood). If the bleeding was from the lower gut, then blood may be able to retain its red fluid consistency. However, if a person is constipated then even bleeding in the lower gut can appear dark and degraded. This is because it is retained in the system for longer than normal and the air in the gut plus colon bacteria break it down.

On the other hand, bleeding in the upper gut could appears as bright red and fresh in the stool if a person has diarrhea. This is because the movement of food is so rapid through the gut in diarrhea that the blood does not have time to degrade. The bright red and fresh blood in the stool is known as hematochezia and one of the most common causes i rectal bleeding due to hemorrhoids.

It is important to differ between melena and black bowel movement from reasons, other than bleeding. Sometimes a black discoloration of the stool occurs with certain foods, supplements and beverages without any bleeding. However, the term melena refers specifically gastrointestinal bleeding that causes dark tarry stools.

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  • mariam Mohan

    Hi, I have been suffering from stomach problem for a long time, gets better in between i am off non veg food. I feel better after taking vegetarian food, but still at times i do get shooting pain. My stool is fine, no blood no mucus. I am not losing weight. I have a good appetite too. I was planning on getting an endoscopy done. IBS is what i have i feel. I am taking VSL3 probiotic med and its helping. But still cant explain as to why i get shooting pain at times.

    • Hi Mariam. Pain on its own with no other symptoms is difficult to diagnose. There is no certainty that it is arising from the stomach or any other part of the digestive tract. Yes it could be IBS but your doctor will first have to run further tests to exclude other possible conditions. Don’t make any assumptions just yet. Rather follow the advice of your doctor.

    • COJenn

      They won’t say ibs till they rule everything else out and I would think since I have had many of both, I have lost my nom to colon cancer in 7 weeks from diagnosed…but the endoscope only goes mouth to tummy…your symptoms sound lower since your stomach lives under your left ribs and barely under that….it might sound weird or stupid.. but a veggie diets have most people produce tons of gas and with your intestine looping when it gets stuck at the top of a loop, it feels like stabbing pain.. it happens with most fiber filled veggies, beans, things like lentils…I would try a gas reducer like gas ex or no beans or something close…if its sharp pain that comes for a bit, suddenly, it goes away, seemingly by itself, just as quick as it came, gas is my well educated guess…also try walking even though it hurts so bad when it happens I know you don’t want too…then it can even hurt so bad you feel like its a heart attack…but if your pain is lower than ribs on the left…then the teat that would “look” is a colonoscopy, good test, prep sucks, you literally pee from your hinny from the clean out process, its expensive, and it really depends on how often, how bad, you hurt, but more if it changes with diet…its not colon cancer like my mom…if its gas it is normal…I saw a study most er’s get more that 3 people a shift on average where this is the diagnosis, and most people over their lives to a few times because the pain is sudden, really bad, and it feels serious, we all leave feeling dumb…but I can say if your gut says go, go. I had a bad backache..tried heat, positions, lots of stuff all day, finely went, was sent home still really not able to walk and had I called or something I could now be paralyzed since I ruptured disks SLEEPING! and have spine involvement! so a bit of a shift….no more anything from mid back down…so even though I stayed after I was discharged because my gma was upstairs in the rehab after breaking her leg, I took a wheel chair up, since I couldn’t drive home and I was told in 6 hours the shot I was given would be working, still crying, I was back in 5.5 hours…so sometimes you have to fight when your gut says they are missing something…listen! I was admitted for over a week…I am still in physical therapy, medication, and then more things to help not have to have spine surgery…also no matter if you have both the scope you spoke of and the colonoscopy…they can’t see the middle…you may need a ct/mri, they may make you drink barium, if so take the day off, if makes some sick, I vomited for 8 hours at work since they would not let me off…but I figured I have had cts before, even with dye.. its fine…nope, wasn’t.. just needed bed though…you may be like me and at 8 hours, vomited so much almost everyday, lost many teeth, well they were damaged badly by the acid.. and I still have no solid answers, well I have had 6 docs, and I have 5 answers…2 agreed, but through figuring stuff out with the meds, listening to ny body if what and when to eat..what meds if any since every doc says take these everyday. but that made stuff worse…so I took notes, what worked, what didn’t, with meds, otherwise I would of had it with a different name as weak times…but your notes, copies of any scans, and all that in a binder will be your best resource!