I’ve had a colonoscopy (without pain relief) where they took biopsies. The doctors said the biopsies wouldn’t hurt because the colon couldn’t feel pain, and they were indeed painless. The amount of air they pumped in was horrifically painful however.
Trapped gas sounds trivial, but can also be extremely painful. Ulcerative colitis also hurts. So does diarrhoea.
So how do these pain mechanisms work? What causes the pain, if the interior of the colon is unfeeling?
In: Biology
A simple way to think of the colon and pain is to relate it to the skin. Lots of different things can cause different types of pain in the skin. There’s pressure, heat, cold, cuts and probably a few more. There is a specific type of nerve ending to sense each type of pain.
The colon (the entire intestine, in fact) has only two types of pain receptors – ones that sense stretching, and ones that sense lack of oxygen (which happens when the colon is starved of blood). Trapped gas will make the colon wider, which sets off the stretching pain receptors. Biopsies don’t hurt because the colon lacks the nerve endings to sense cuts and bruises.
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Doctor here, please let me know if I haven’t explained well enough:
Pain in organs (visceral pain) is very different to the pain you’re used to experiencing in your skin/muscle (musculoskeletal pain). We have very sensitive pain receptors which localize all sorts of pain in the skin/muscles (including touch (pressure, cutting)/temperature/inflammation) – we have evolved this because it is very important we know quickly and accurately if there’s a problem in our musculoskeletal system.
Internal organs have pain receptors, but not for touch – someone could be cutting your internal organs and you wouldn’t feel it. They do have pain receptors for stretch (e.g. Bad gas), inflammation (e.g. Appendicitis) and when they’re oxygen starved (e.g. Heart attack). These pain receptors are poorly mapped by the brain, which is why heart attack pain can be felt as jaw or arm pain, and pain in the liver can be felt as shoulder pain.
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Gastroenterologist here.
Since when does the colon not have pain receptors? Your entire GI tract is innervated heavily, both with nerves inside (the enteric nervous system), and nerves that project onto your skin (somatic nerves). Distension and gas absolutely cause pain, and your body is very finely tuned to detect when a portion of your bowel is distended. One of the most common causes of chronic pain is [irritable bowel syndrome](https://en.wikipedia.org/wiki/Irritable_bowel_syndrome), which causes intense pain with contraction of the colon and distension with gas. In short, there are about as many nerves in your GI tract as there are in your spinal cord. Many of these nerves are pain fibers.
Furthermore, there is something called the brain-gut axis that connects all this machinery to your brain, which is constantly being informed of the status of your GI tract. Hence the reason that your stomach hurts when you have anxiety.
The reason the doctor said that is because the part we biopsy, called the mucosa, is above the shallowest nerve layer, called the submucosa. Deeper biopsies can certainly hurt, but the biopsy forceps are very tiny, and we just get a little pinch of tissue.
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