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Biology 101- Anal Canal and Rectum difference

Jul 5, 2007

Doctor Robert,

Good morning. Whats up? I can't believe in 2007, with the world at our fingertips for more than a decade thanks to the Internet we yet have questions on HIV from trying speedos on. My 13 yr old niece knows better. Come on people- If youre this crazy, stick to shopping online!!

Ok, my questions to you.

As a 30 something gay male I've tried to do a little reading on the anus. Its always been a taboo topic growing up in a Christian family- certainly not something you would discuss over dinner nor ask your family doctor. ;) What is the difference between the rectum and the anal canal? And I understand there are 2 muscles in the ass- the internal involuntary sphincter and the external sphincter, which is voluntary. How deep does the external sphincter run? Is it an inch? Is the anal canal thicker than the rectum?

I wish you would answer my question or point me to a good source. I think its time we get the discussion back to Biology and worthy of a Doctors time.

I appreciate the work you are doing here. Stay well, be happy.


Response from Dr. Frascino

Hello NTJ,

This is an HIV information site and not really a biology 101 class, so I'll be very brief. The rectum is the final part of the intestinal tract. It's 4-5 inches long and passes through the pelvic cavity to the anus. The anus is the external opening of the rectum. Its closure is controlled by two anal sphincters, one internal and the other external. For additional information, any biology 101 textbook should do the trick.

Dr. Bob

AIDS Dementia

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