Human Digestive System

digestive system diagram

The human digestive system breaks down food so it is available to the body for energy, cell growth, and repair. Here we explain the organs and processes that enable our bodies to convert food into sports performance.


Digestive system function

Video explaining the structure, function, and passage of food through the digestive system.

Breaking down food for use as energy, cell growth and repair is the primary function of the digestive system. It does this mechanically and chemically with enzymes. A number of organs and processes combine to break food down into smaller molecules.

Digestion occurs in a series of tubes as food passes through the body. A number of other organs contribute to digestion by providing enzymes for the breakdown of food.

Organs of the digestive system

The following are digestive system organs:


The mouth is the starting point of digestion. Here the process of chewing starts to break down food and enzymes such as salivary lipase and amylase also start to chemically break down the food.


Once you swallow the food moves into the Oesophagus where continual waves of involuntary contraction push the food into the stomach.


The stomach has both a mechanical and a chemical function in digestion. The stomach muscle is smooth, involuntary muscle. This means it automatically contracts without us consciously telling it to. The upper part relaxes to store a large volume of food.

The lower muscle then contracts in a rhythmical manner in order to churn the food. It mixes it together with the gastric acid (mainly hydrochloric acid) and digestive enzymes. The digestive system enzymes Pepsin, Gelatinase, and Gastric Amylase, and Lipase break it down further.

The stomach contents then empty into the small intestine.

Small Intestine

Whilst in the small intestine food is subjected to yet more enzymes. These are from the Pancreas and from the glands within the intestine walls which break down carbohydrates and proteins.

The gall bladder stores and releases bile from the liver into the small intestine. Bile dissolves fat so that it can be digested by the other enzymes. Again, rhythmic smooth muscle contraction continues within the small intestine and pushes the digesting food through its narrow tube.

Once the food completely breaks down into its individual components, blood absorbs it through the intestinal walls. Specifically via capillaries which surround the intestine.

Intestine walls contain numerous folds covered in finger-like projections called villi. The process is faster because vastly increases the surface area of the intestine wall for molecules of digested food to pass through.

Large Intestine

The large intestine continues the food’s journey and is the body’s last chance to absorb any water and minerals still remaining. The rest of the contents of the large intestine is waste such as undigested pieces of food and fiber. This is passed through to the rectum where it is stored until you go to the toilet!

Labelled digestive system

The following labelled digestive system diagram shows the location of the major organs involved.

Digestive system

Digestive system facts

I bet you didn’t know.

At birth, we have about 10,000 taste buds on the surface of the tongue, in the throat, and on the roof of the mouth.

It is a myth that the tongue is the strongest muscle in the body. The tongue is made up of 16 different muscles and as yet there is no conclusive evidence that it is the strongest. If all the muscles in the human body had a weight lifting contest then the masseter or jaw muscle would come out top.

The appendix has no function in the human body. Charles Darwin thought that it was used for digesting leaves when we were primates.

An adult stomach has the capacity to hold around 1 litre of food and liquid. The stomach can expand though and it is believed to be able to increase its capacity to between 2 – 4 litres.

About 11 liters of fluid, digestive juices, and digested food are circulated around your digestive system.

On average 1 to 1.5 litres of Saliva is secreted into the mouth every day.

It doesn’t matter which way up you are for food to reach the stomach – you can be upside down and the food will still get there and throughout all the parts of the digestive system.

The role of the mouth is not only mastication (chewing) but also to get the pulp to a temperature that is acceptable for the rest of the digestive tract.

Gastric Acid contains Hydrochloric acid (about 0.5%) which can corrode metal, it has a PH value between 1 and 2. Anything with a PH less than 2 is considered as “strong acid” and can burn the skin.

The stomach lining is replaced continuously, and it is completely replaced approximately every 5 -10 days.

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