How the bowels work

The digestive system: What it is, what it does, and why it is important 

The digestive system performs a fascinating but complex process. It consists of all the organs involved in breaking down food, absorbing nutrients, and eliminating waste products. 

The small intestine 

The digestive process starts in your mouth when you take a bite of food. As you swallow your food, it travels through your oesophagus into the stomach, where it is broken down into smaller pieces and mixed with digestive fluids. This is then passed into the small intestine, where most nutrients, vitamins and minerals are absorbed. 

The large intestine 

When the small intestine has done its job, the large intestine takes over. In the large intestine, the remaining water and salts are absorbed, which changes the remaining waste products from liquid to a firmer consistency. The stool is then pushed through the intestine towards the rectum by a series of muscle contractions, known as peristalsis. A healthy bowel will typically have 3 to 4 major peristaltic movements per day, which are typically triggered after meals. 

The time it takes for food to pass through the digestive system is called the ‘transit time’. It changes from person to person, but the average transit time is 2.4 days for women and 1.9 days for men. 

The rectum 

When stool reaches the end of the colon, it is passed into the rectum, where it is stored. As the rectum fills with stool, it expands. This triggers nerve signals that are sent to our brain, making us aware that it’s time to find a toilet. At the same time, the internal sphincter relaxes by reflex and stool moves down towards the anus. When the individual is ready, they consciously allow the external sphincter to relax and stool is expelled. 

Both the internal and the external anal sphincters are contracted between toilet visits, helping to keep the individual continent and preventing leakage.