Know your arse
In this section you will find information about the arse and how it works. We believe that knowledge can help us have a better sex life. Knowing how our bodies work – what can happen when we have sex, how to look after our bodies and how to keep them working – can help us enjoy anal sex more.
The external sphincter is a muscle that holds the anal canal in shape. It stops you from shitting when you don't want to and can stop things from getting up your arse too. There are lots of nerves within your external sphincter so it can feel sensations of hot and cold, expansion and touch. This muscle is controlled by the central nervous system, the same system that controls the voluntary movement of our fingers and toes, etc. This means that we are able to learn to tense and relax this muscle at will (most people can clench).
The internal sphincter shares the same functions as the external sphincter – to prevent any unwanted entry or exit and to hold the anal canal in shape. This muscle is controlled by the autonomic nervous system, the system responsible for controlling blood pressure, respiration rate and other 'bodily functions'. This makes it harder, although not impossible, to learn how to control this muscle.
This short tube-like canal is the final passageway in the passing of shit. The area provides some lubricant to ease the passage of the shit. The outer two thirds of the anal canal, the part you can see when you spread a guy's arse open, is sensitive to touch, temperature and pressure. The inner third – the part that changes from flesh colour to bright reddish pink colour as you spread the arsehole open – is less sensitive to touch, but very sensitive to pressure. The whole of the anal canal is made up of folds of soft smooth tissue that give it a great capacity for expansion. The outer two thirds are made up of the same soft sensitive tissue visible at the opening. The inner third, the reddish pink bit, is a mucous membrane. This absorbs fluids into your bloodstream. If the outer layer of the mucous membrane is disturbed (by douching, dildos, or even just from fucking) it makes the arse more vulnerable to infections like HIV.1 At the top of the canal are the 'anal sinuses' that are responsible for producing the snot-like lubricant or anal mucus that occurs naturally in your arse. Research indicates that anal mucus is the body fluid that can have the highest concentration of HIV.2
There are three anal pillows attached to the internal sphincter muscle which run the short length of the anal canal. The anal pillows inflate with blood to prevent shit from coming out of your arse, when you don't want it to, and to prevent things going up your arse too. They need to partially drain to allow you to shit (or allow anything in). They do this by responding to signals transmitted from the brain. You can feel sharp stabbing pains when the pillows aren't drained and you are trying to shit (especially if you strain too hard) or get fucked (or stick something up your arse). The veins that supply the blood to the pillows are the ones that can become piles, which are also known as haemorrhoids. It's these pillows that place large quantities of blood in your arse and account for the blood found during or following anal sex. It's this blood you can see on toilet tissue after you have been fucked or passed a particularly large or hard stool.
This is the last section of the intestines which, along with the colon above it, absorbs excess water from your shit. The further away from your stomach the waste matter in your intestines is, the drier it gets. When you have diarrhoea and you pass watery shit, this is because your body shuts down the absorbing function in response to the infection it thinks is in the contents of your bowels or the water. The rectum only contains shit when your bowel is full. So a good dump before you get fucked should be all you need to do to be clean up there and significantly reduce the chances of some unpleasant mess. This part of your arse is like a sponge as it is so absorbent. When a man ejaculates (cums) inside the rectum, the semen is absorbed directly through the wall of the rectum so that any virus in his cum, such as HIV, has an easy route into the bloodstream. Research suggests that there are some differences in the cells that make up the lining of the rectum compared with those that line the anal canal. These differences make it easier for the lining of the rectum to be disturbed or damaged and so it may be more susceptible to infections.
The rectum contains relatively few nerve endings and is therefore less sensitive. In general it transmits mostly sensations of pressure. As it is the continuation of the anal canal, the rectum is another tube-like structure of between five and nine inches long, made of loose folds of soft smooth tissue. It's worth remembering that the average length of a British cock when erect is between five and six inches, so most cocks only get as far as your rectum. Normally the rectum is more open and spacious than the anal canal, but also shares its capacity for expansion.
While the rectum is tube-like, it's not a straight tube. Instead it has two curves along its length. The lower rectum tilts forwards towards the navel (caused by the pubo-rectal sling), and after a few inches, curves in the opposite direction towards the backbone. The second curve is usually more 'adaptable' than the first and rarely a source of discomfort. The pressure sensation in here when shit is present sends the message to your brain that you need to empty your bowels, which is why having a cock up there can make you feel like you need a shit. When you have a cock or a toy in your rectum and you feel like you need to shit, try reminding yourself that your brain is getting this message because your arse is full of cock.
Chemicals or spermicidal lubricants, such as nonoxynol-9, easily irritate the lining of the rectum.3 This can cause chafing where the lining of the rectum dries up and starts to peel, similar to the way your skin peels after sunburn, causing it to become itchy and very unpleasant. This can remove layers of cells from the lining of your arse making it more vulnerable to infection.
Rectal muscle coat
These are the muscles that support the entire length of the rectum. They tighten in stages along the length to move shit through the rectum and out into the world. This process of muscle contractions used to propel the shit down is called peristalsis. That's the same process that snakes use to propel their food through their bodies – muscles constrict and expand to push food down through the intestines.
The only sensations that the rectal muscle coat responds to are pressure and bulk. Some men say they can feel it when a man cums inside their arse, but physiologically that's not possible. It's probably the cock spasms as the man ejaculates that they can feel against the sphincter, or the cum as it dribbles out of the arse across the sphincters, which are responsive to temperature, touch and movement.
The tension level of these muscles varies from person to person. Rectal muscles are not as powerful as the anal sphincters, but if they are tense the insertion of anything can be painful.
This is a strong supportive muscle that creates the first curve in the rectum. It's one of the most powerful muscles in the body after the tongue. The muscle responds to pressure or poking by clamping down to close the rectum and this can prove painful when getting fucked, fingered or toyed with. It's when a cock stabs this that you get that 'whoa get the fuck out of me' sensation. Straightening out the rectum a bit by adopting a position where the knees are drawn up will help avoid this. Try squatting down over the cock, lying on your back or your side with your knees drawn up to your chest, or on your knees bringing your chest as close to the bed/floor as you can.
The prostate gland produces fluids that are added to cum and, because it surrounds the urethra, it also helps control the flow of piss. A lot of the pleasure we can feel when getting fucked comes from the cock rubbing against the prostate, and for this reason it is often referred to as the male g-spot. Here's how to find your partner's prostate:
Get your man to lie on his back with his legs drawn right up, his knees held to his chest. Lubricate his arse, and then insert a well-lubricated middle finger into the arsehole. As the finger goes in, curl it up so that the tip of the finger is hooking up and pointing behind the pelvis towards the cock. The prostate is there about an inch and a half in. It feels warm, rubbery and smooth. Flick or run the tip of your finger crossways against the prostate. This usually gives the owner sensations of intense pleasure.
Sigmoid colon⁄anal fold
This is the collection place for shit before it passes through the rectum into the anal canal and on into the world. The nerve endings here are similar to those in the rectum, responding only to sensations of pressure. It's also able to expand to larger than its normal size. When a cock, or something similar, is put up your arse, usually only the anal canal and the rectum are involved. However dicks, dildos or anything longer than nine or ten inches may pass through the rectum into the lower colon. This usually occurs without difficulty, as the muscles tend to relax at the same time as the other anal and rectal muscles.
1 Roehr B, Gross M, Mayer K. Creating a research and development agenda for rectal microbicides that protect against HIV infection: report from the workshop: Baltimore, Maryland, 7-8 June 2001.
2 Zuckerman RA, Whittington WLH, Celum CL, Collis TK, Lucchetti AJ, Sanchez JL, Hughes JP, Sanchez JL, Coombs RW. Higher concentrations of HIV RNA in rectal mucosa secretions than in blood and seminal plasma, among men who have sex with men, independent of antiretroviral therapy. Journal of Infectious Diseases, 2004;189:156-161.
3 Phillips DM, Sudol KM, Taylor CL, Guichard L, Elsen R, Maguire, RA. Lubricants containing N-9 may enhance rectal transmission of HIV and other STIs. Contraception, 2004;70(2):107-110.