Your rectum and anus

Your rectum and anus are the very last stop in your digestive system.  They are at the end of your large intestine and receive the waste products that are left over from the food you have eaten, about 24 hours after you first ate it.  At this stage, all of the nutrients have been absorbed by your small intestine and the last few vitamins, minerals and water has been absorbed by your large intestine.  All that is left is the solid waste called faeces, which is sometimes known as a stool or poo!

Faeces are solid but they still contain mostly water (up to 75%) as well as bacteria (alive and dead), undigested nutrients like protein or fats, mucus from the intestines and fibre (which humans cannot digest).  Although you cannot digest fibre, it is really important in digestion as it helps to bulk up your food and move it along your intestines at the right rate to keep them healthy. 

Faeces can loose lots of water if you are dehydrated (when you don’t have enough water in your body) which makes them very difficult to move along your intestines and very difficult to push out from your anus.  Dehydration is sometimes the cause of constipation.  On the other hand, if your faeces have too much water, they will pass through your large intestine too quickly – a condition known as diarrhoea.  Diarrhoea can be very dangerous as it causes very quick dehydration and your body also expels lots of a particular type of salt from your body, which can make it malfunction.  

You may notice that faeces can smell pretty bad.  This smell comes from the bacteria that help you to digest the food you eat - they produce gas as they ferment your food.  The smell and build up of gas really depends on what you eat!  Some foods like beans and processed food (a lot of the stuff that comes ‘ready-made’) make sure that lots of gas builds up while others have no effect at all.  You know what happens when there is a build up of gas in your body – it is expelled at great speed and usually with a loud noise from your body!  If you have eaten lots of food that make your faeces smell, this will also make your gas smell really bad.  Also, if you don’t chew your food really well, it can go through your digestive system in large lumps.  This means that nutrients are not absorbed properly and also that bacteria ferment even more – which can cause smells to get worse.  In general, however, if you have a healthy diet, with lots of natural foods, you won’t have many problems!