Why does rectal cancer give a sense of incomplete evacuation

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Hello everyone,

1.I was wondering what is the exact mechanism that rectal cancer gives a sense of incomplete evacuation after defecation (Tenesmus in scientific language). Also why is this is not present in colon cancer higher up eg in ascending colon cancer and only lower down like rectal cancer?

2. Also while we are at it. Why does alteration of bowel habits occur in rectal carcinoma?

What I think is, due to the colon lumen obstruction by the cancer first you get constipation and faeces build up. The bacteria work on this faeces and break them in to liquid, causing diarrhoea. Am I right?
 
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Choppy
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I think there are a number of answers to these questions. You might want to start by looking up rectal tenesmus. The symptom can occur with just about any condition that enflames the bowel. The nerves that signal the need to pass fecal matter can be irritated by the inflamation resulting in an uncomfortable, painful, and anxiety-inducing condition. Obviously one would have more of these nerves in the rectum compared to higher up the tract, which I suspect would be why the symptom would be more likely with cancers in that area. Although, do you have any evidence of this?

As to the second question, I don't think you can chalk it up to a single cause. Whenever you have inflamation of the recutm and surrounding tissues this is going to disrupt natural patterns. The biome is going to change. The individual will be more sensitive to the presence or absence of fecal matter or gas. Anxiety, pain, and/or discomfort will likely force the individual into altering his or her habits - consciously using the washroom more often, subconscioulsy avoiding prolonged periods where washroom access may be limited. Often the person will choose to alter his or her diet. On top of that, the person has cancer. Cells that are normally supposed to be doing one thing - providing a lining for the bowel for example - are doing something else. You have new vasculature growing to feed the cancer.
 
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Thanks for the great response Choppy.
 

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