Why does rectal cancer give a sense of incomplete evacuation?

[scilearner]

Hello everyone,

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?

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[StringJunky]

Probably we have more sensors lower down. If you've got a fixed voluminous mass in the rectal space you will have the feeling of never being empty ...simple pressure.

[scilearner]

Thanks for the reply String Junky. I thought that too, but I was wondering if there was some other phenomenon beside the obvious. Something to do with rectal sphincter may be. Did you just think and give the answer or is this from some reference. You might well be right may be there is no serious phenomenon, I just asked to check.

 

1. 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?

[StringJunky]

What you're asking, I suspect, is "how long is a piece of string?". There are so many possible combinations of factors. https://en.wikipedia.org/wiki/Diarrhea.