The word ulcer is a very general term. One can have ulcers on the skin, in the mouth, esophagus, stomach, duodenum, small intestine, large intestine or colon, and bladder. Doctors can even refer to ulcerations of plaques in the arteries as ulcers.
I will assume that you are asking about ulcers in the stomach or intestine, which are the most common type of serious ulcers, and also the type most likely to bleed. These ulcers are also referred to as peptic ulcers, because of the stomach enzyme pepsin.
Normally, everyone’s stomach secretes acid. Actually it’s pretty strong hydrochloric acid, sufficient to lower the stomach pH to one at times. (pH is the common chemical designation for the acidity/alkalinity of fluids. One is very acidic, while 14 is very alkaline and seven is neutral, neither acid nor alkaline.)
Why did we and other mammals evolve such a corrosive environment in our stomachs? Why can’t we digest our food at a nice, non-corrosive pH of around seven? Our blood for example has a pH of 7.4, slightly alkaline while our urine is usually a little acidic with a pH 5 or so. The very acidic environment of our stomach and upper duodenum certainly creates problems for us, ranging from heartburn to bleeding ulcers.
The answer as to why we have a pH of 1 to 2 in the stomach relates to the activity of the pepsin enzyme, which begins the first essential digestion of proteins. Many of the amino acids that make up proteins are crucial to our health. Since we can’t make them internally, we have to get them from our food. To do the job the enzyme pepsin works best at the very acidic pH of 2. Why we developed a system that requires that much pH to digest our proteins I can’t say, but because of all that acid some of us get peptic ulcers.
For most of the twentieth century doctors believed that the cause of ulcers was only related to the acid and pepsin production of the stomach, and a presumed failure of protective mechanisms in the stomach and duodenum to prevent the corrosive combination from creating an ulcer. So we were astounded by, and refused to accept for quite a few years, research that showed that peptic ulcers were actually related too and maybe caused by an infection with a bacterium called Helicobacter pylori.
Exactly why infection with the bacterium permits a person to develop an ulcer is not known. Many people infected by H. pylori do not get ulcers, but careful studies have shown that about 95 percent of people with duodenal ulcers have that infection, and about 80 percent of people with stomach ulcers do as well.
Now the first line treatment of ulcers, whether in the stomach or the duodenum, is to clear the H. pylori infection. This major change in understanding and treatment of the condition has greatly reduced the need for ulcer surgery.
Some ulcers still require surgery, often emergency surgery. These are ulcers that either perforate, or bleed. Ulcers bleed because they erode little blood vessels, and ooze blood, or occasionally they erode a good sized artery, and bleed rapidly.
So yes, ulcers can definitely bleed, both slowly by oozing, and very rapidly, by spurting arterial blood.
How do you know if an ulcer is bleeding?
That’s a complicated question, and one that depends on the symptoms the person was having before the ulcer began to bleed, and the rate of the bleeding.
People with an ulcer who experience the typical acidic stomach pain when they haven’t eaten may find that their pain is reduced when the ulcer starts to bleed, since the blood in the ulcer itself neutralizes the acid and reduces the pain. On the other hand, some people with ulcers never experience pain, and may have massive bleeding with no symptoms at all other than faintness, vomiting blood, or passing blood filled stools. Stool with blood in it is often referred to as melena, a black stool in which the blood has been partially digested and turned black. If the bleeding is really massive, the stool may be liquid and maroon colored.
Such massive bleeding is a true emergency, since a person can go into shock and die quickly if they are not given blood transfusions, the source of bleeding is discovered and the bleeding is then stopped. With massive bleeding it’s common to do an endoscopy to find the source of the bleeding and cauterize the bleeding artery. If the bleeding is slower, and is only resulting in black stools and perhaps anemia from blood loss, then x-rays or endoscopies to find the bleeding source can be done. If an ulcer is shown, medical treatment may be all that is necessary.
I want to emphasize that vomiting blood is a serious emergency and demands immediate attention. Passing maroon colored liquid stools is a similar emergency also requiring immediate attention. Passing formed black stools may indicate bleeding, and should always be investigated, but is not an emergency if the person feels well and is not dizzy when standing up.
Bright red blood mixed in with the stool is probably not from an ulcer, but must be investigated, since it could be bleeding from a colon polyp or cancer. Simply having blood on the toilet tissue after moving one’s bowels, especially if hemorrhoids are present or there is irritation around the anus is much less serious, but should be investigated if it persists.