How the bowel works

 

It really is worth taking time to understand how the bowel is supposed to work so you have a better grasp of problems bowel works that can arise in MS and recognise ways to deal with them.

 

 

The digestive system

 

 

 

 

 Illustration showing the various elements of the digestive system

 

 

 

 

The bowel is part of the digestive system. Put simply, the digestive system absorbs the goodness from food that you eat, and expels the waste products from the food that the body cannot use. The small bowel (or small intestines) is the part of the bowel where the useful parts of food are absorbed. The large bowel or colon is the waste processing part of the system.

 

 

The colon (large bowel)

 

 

 

 

 An illustration showing the motion of contraction across the colon

 

The small bowel delivers 1 to 2 pints (500 to 1,000 mls) of waste to the colon per day. Waste is the consistency of thick pea soup when it enters the colon. It is the job of the colon to absorb fluid from the waste and gradually form it into stools (also called faeces).

 

Whether stools are soft or hard will depend on how much water has been absorbed from them: the longer the time spent in the colon, the harder the stools will be. Food usually takes one to three days for the body to process it, and 90 per cent of that processing time is spent in the colon.

 

You can think of the left side of the colon and the rectum as a storage tank at the end of the large bowel. Stool does not enter the rectum from the colon on a continuous basis. Instead, waves of contractions or mass movements happen from time to time along the colon to send waste to the rectum. Waves are often set off by the so-called ‘gastrocolic reflex’, where having a hot drink or a meal can set off a pressure wave. Stool entering the rectum will lead to a feeling that you need to empty the bowel, which doctors describe as ‘the call to stool’.

 

 

Anal sphincter muscles

 

 A diagrame showing the 'rings of muscle' in cross-section, and a side view.

 

 

 

 

 

The anal sphincter muscles are two rings of muscle around the anus – the exit from the bowel. They form part of the ‘pelvic floor muscles’.

 

When stool moves into the rectum, the internal anal sphincter relaxes automatically (a reflex or involuntary action) and allows stool into the top of the upper anal canal. Nerve endings in the anal canal can tell between wind (also called gas or flatus), loose or runny stools that need urgent attention, and a normal stool. A person can then decide when to use the external anal sphincter to open the bowel (a voluntary action). If it is not convenient, squeezing the external sphincter can push the stool back to the rectum. If it is convenient to pass the stool, you can relax the muscle.

 

Compliments of:MS Society, UK