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Rectum, anal canal and arsehole

Rectum

Around the connecting tube between your sigmoid colon and rectum is a ring of muscle that angles the tube in such a way as to close it off. This sphincter muscle regulates the shit leaving the sigmoid colon; without it, your rectum would fill up continuously and you would be shitting all the time. Your rectum is a stretchy four to five inch (10-13cm) muscular tube that can stretch to the size of a clenched fist (when full of shit) or a hand.

Anal canal and arsehole

Below your rectum is the anal canal, 1-2 inches (2-5cm) long which ends in your arsehole. The surface of the rectum and the anal canal is usually covered with a thin layer of mucus or natural lubricant designed to help with shitting and which also helps offer protection from infections. If you rub the surface, you quickly exhaust the supply of mucus which is why you need additional lubricant when putting anything up the arse.

At the bottom of the anal canal is another sphincter muscle made up of two smaller interconnected rings of muscle. One of them is not under your direct control but responds to internal body messages when the rectum is full or when you cough – the muscle tightens. When the muscle doesn’t work properly you leak. You have more control over the other muscle which you can relax or tighten at will. Try it now – you see control is everything!

Rectum | Anal canal | Wikipedia