How does digestion begin?
When you digest your food, you break it down so your body can extract the nutrients and absorb them. This digestive process begins in the mouth where the teeth and tongue chop large pieces of food into smaller ones. The salivary glands release saliva into your mouth to mix with the food. An enzyme in saliva called salivary amylase starts to digest carbohydrates such as sugars and starches.



How does food move down into the stomach?
Once the food is chewed and softened in the mouth, the tongue pushes it to the back of the throat, where muscles propel it down the oesophagus (or gullet). The food passes from the oesophagus into the stomach through a muscular one-way valve, the lower oesophageal sphincter.

What does the stomach do?
The stomach is a short-term food-storage container. This means you can eat a large meal quickly and digest it over an extended time. When full, your stomach can hold about one litre of chewed up food. The stomach has three main functions.
It stores food so that you can eat enough at one go to last you for several hours.
It churns and crushes food and produces powerful acids and enzymes that help break down the constituents of food into simpler chemical compounds.
Stomach acid works on food for several hours to destroy most of the bacteria and other micro-organisms that may have contaminated it.

Where does food go when it leaves the stomach?
After the food has been liquidised by the stomach it is pushed onwards through another valve, the pylorus, into the duodenum. The duodenum is immediately outside the stomach and is the first few inches of the small intestine. In the duodenum:
More chemicals are added to neutralise the stomach acid
The pancreas produces enzymes that are sent to the duodenum to help digest carbohydrates, fats and proteins
Bile from the liver enters the duodenum to help digest fats.

What happens in the rest of the small intestine?
Food passes from the duodenum into the rest of the small intestine which is six metres long. It is called the small intestine because even though it is long, its diameter is smaller than that of the large intestine.
In the small intestine:
The chemical breakdown of food is completed
The chemical constituents of the meal are absorbed into the blood and lymphatic vessels.

What happens in the large intestine?
The main jobs for the large intestine are:
To reabsorb the water that is used in digestion
To eliminate undigested food and fibre.

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