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.