How the bowels and anus work
The colon (large bowel) is the lower part of the gut. It is more than 1 metre long. Its job is to store faecal material and remove fluid from it, so that faeces are fairly solid and the body does not waste water. The colon may absorb 1 litre of fluid a day. The colon contains lots of helpful bacteria that break down food residues (turning some of them into wind and manufacture some vitamins. The muscles of the colon gently contract and relax all the time, rolling the waste matter about like clothes in a washing machine. Several times a day, usually after meals, the colon makes some big muscular contractions to dump the faecal material in the rectum beyond it.
The rectum and anal canal. The large bowel (colon) leads into the last part of the gut, which is called the rectum. It is about 12–15 cm long. The final 3 cm of the gut is called the anal canal.
When faeces arrive in the rectum, it sends a message to the nerve centres in the spinal cord, and these send a message to the sphincter muscles of the anal canal, making them relax to open the anus. If it is inconvenient for us to have our bowels open, the brain sends a message to the spinal cord to prevent the ‘open anus’ message being sent. We are not aware of this until the rectum becomes very full, when we have to make a conscious effort to keep the anus closed. When we allow the anus to open, the muscles in the wall of the large bowel and rectum contract to push the faeces out. The wall of the anal canal wall is very muscular. The muscles keep the anus closed, except when faeces (‘stools’) are passed.
- The ring of muscle at the top of the anal canal is called the ‘internal sphincter’. This muscle is not under our conscious control.
- The ring at the opening of the anus is called the ‘external sphincter’. This muscle is more like the sort of muscle that we have in our arms and legs, and we are able to control it (until the urge to pass faeces becomes overwhelming).
It is obvious that in babies the system of nerve messages that keep the anus shut is not in place – babies pass faeces as soon as the rectum fills. After about 18 months of age, the system develops, but in some children this can take a long time.
A network of small veins lies under the lining of the anal canal. These veins form a soft, spongy pad that acts as an extra seal to keep the canal closed until you go to the lavatory. The lining of the gut is very slimy (so that faeces can pass along easily); the extra seal stops the slime (mucus) from leaking out. The spongy pads can become swollen. When this happens they are called piles (haemorrhoids).
Written by: Dr Margaret Stearn
Edited by: Dr Margaret Stearn
Last updated:
Saturday, February 13th 2010
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Posted by Charlie on 07/02/2010 at 06:20:00 pm
Life long sufferer from IBS.For peace of mind,always have to be within 2 minutes of a toilet. My lifesaver is Imodium,(Loperamide Hydrochloride,2mg capsules)Two of these taken on the evening before an outing,ensure reasonable safety. Note. This medicine is used for social purposes and is not a cure. Good luck.
Posted by kaz on 06/02/2010 at 11:21:00 pm
i had an hysterctomy 3 years ago and then further surgery to correct and during this op my bowel was perforated and then i had further surgery and had small bowel removed and since have been in constant need of opening my bowels after every thing i eat or drink - have you got any advice or tips please - iv'e no life can't do anything or go anywhere unless i take immodium and i am in constant pelvic pain.
Posted by Anonymous on 04/01/2010 at 05:01:00 am
So many of the comments I see here relate to improper digestion, and elimination, of the foods we eat, and the inability for nutrients to be absorbed into the blood. Helene Silver has several GREAT books about all this, one is called "The Body-Smart System", another is called "Rejuvenation". Even if you don't have the stamina to do her 21 day detoxification program, the info (in the Body-Smart System in particular) is critical reading. Due to the type of eating habits we all have become accustomed to, our bodies are very toxic, resulting in the kinds of "symptoms" noted here. We are sorely in need of detoxifying our bodies and bloodstream and changing what and how we eat. Hope this helps. (I come from a family with several members who died of colon cancer, and have been making changes all my adult life. Keeping the colon clean, nourished, and eliminating efficiently is paramount.
Posted by Anonymous on 25/12/2009 at 03:22:00 am
I have a problem with my head. Whenever am reading through the comments i feel great headache because i see only querries wit no replies or solutiom
Posted by Tom on 22/12/2009 at 09:45:00 am
Hi, i have a problem every now and then with my anus sweating and stinging, also when i wipe its as if i havent wiped properly as its always faecas coloured, its as if my anal area is weeping, but it is getting more regular mainly when im working, hope you have some good advise for me Thanks Tom
Posted by mona on 06/11/2009 at 10:28:00 pm
I have aproblem w/ my vowel movements..i don't have the muscle around it so i always have to carry an extra pair of pants because i might have an accident...do you know any doctors that perform this type of surgery. I was told that in the US we don't have these services but that there are doctors in other countries.
Posted by Anonymous on 22/10/2009 at 02:51:00 pm
I am passing bright red blood but I am also experiencing real back pain in the pit of my stomach and sometimes my back but find this topic very embarrassing
Posted by kumari on 07/10/2009 at 12:41:00 pm
Because of medication I get constipated and sometimes the stools get stuck half in and out as they are so hard, I have had to use my fingers to remove the stools, but then get blood, is this just small broken veins.
Posted by Shane on 27/08/2009 at 08:16:00 am
I have been emitting a clear fluid from my anus these last few weeks and it seems to be on the increase ...? It seems particularly bad when I'm asleep.
Posted by Andy on 25/08/2009 at 02:39:00 pm
Because of medication I get constipated and sometimes the stools get stuck half in and out as they are so hard, I have had to use my fingers to remove the stools, but then get blood, is this just small broken veins.
Posted by Anonymous on 07/08/2009 at 01:06:00 am
I've had anal bleeding for a few years now, and I've been checked about 5 times in the last few years by my GP, but they still have no idea what causes my bleeding. Does anyone have any info on this?
Posted by Anonymous on 07/08/2009 at 12:46:00 am
I have great pain this the muscle area of the anus, do you or anyone know of a cure?
Posted by John on 22/06/2009 at 11:12:00 pm
Some time ago I had haemorrhoids removed. Now my anus leaks when I am standing up. I would like a product or process to stop the leak. Any Ideas?
Posted by Elsie on 18/05/2009 at 12:56:00 am
I have diveticulitis, a twisted bowel and irregular spasms that seem to have nothing to do with defaecation. It ruins my sleep and agitates my day. Will preparation H help? Can anything promote regularity and peace?
Posted by gary on 18/03/2009 at 06:30:00 am
i have had two colonoscopys plus banding of haemorrhoids, i now get a red rash around my bum witch is very itchy,could this be caused by leaking fluids from the anus???
Posted by Pat Crowley on 25/02/2009 at 10:56:00 am
I have hyperthyroidism in the form of a toxic multinodular goitre. For past 2 years I have occasional periodic episodes of a thin colorless near odorless fluid leaking from anus during sleep. Once dry the fluid leaves a shiny surface. I've had "piles" since childhood. Thank you
Posted by dave on 20/02/2009 at 02:05:00 am
ichie after bowl movement and i put cream on it ich is there all the time
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How the bowels and anus work
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Fascinating facts
An average person on a typical Western diet passes about 150 g (5 oz) of faeces each day. Faeces consist of about one-third solids and two-thirds water
The solid matter in faeces is cellulose from vegetables, dead cells cast off from the lining of the gut, bacteria, some salts and pigment from bile (which gives them their brown colour)
Most of the waste matter from food is passed out in the faeces within 72 hours, but in healthy people up to 30% may remain in the colon for a week or more
We think one stool a day is healthy, but this is because of the way we have trained ourselves - our bodies are designed to pass faeces more often. Other primates (such as chimps and monkeys) pass soft stools several times a day
Defaecation is a very efficient process, normally taking only 10 seconds. Presumably it has to be quick - animals (and primitive man) cannot run from a predator easily if they are in the middle of passing a stool. This is probably why it is even quicker when we are frightened
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