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Did you know..

..our intestines are over seven metres long? That's almost as tall as a two story house!

There are two main parts to the intestine: the small intestine and the large intestine. The small intestine completes the breakdown and digestion of food, and the large intestine absorbs the water from the contents of the small intestine.

Small intestine: About six of the seven metres that make up the intestine is small intestine, given its name because it is thinner than the large intestine. After leaving the stomach, chyme (semi-digested food) enters the duodenum, and then enters the small intestine. Here is where all our nutrients are absorbed into the blood stream.

The walls of the small intestine have many folds on their surface, and this is to increase the surface area of the intestinal wall so that more absorption is possible.

Say for example we had a piece of paper that was 1m squared. Then we take another piece of paper that measures 1m squared, but has been folded several times. Place them next to each other and they take up the same amount of space. However, if we take the second piece of paper and stretch it out, we see that it is a lot bigger than the first. This is how the walls of the small intestine work.

Villi: Lining the many folds of the small intestine are millions of tiny finger-like projections called villi. These provide even more surface for absorption. Villi are the structures that absorb the nutrients in our food. This is facilitated due to the blood vessels that are found inside each villus. Nutrients are absorbed straight into the blood stream and thus the content of blood vessels leaving the stomach is very rich in nutrients, and this is how our other organs are "fed".

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Large intestine: The main function of the large intestine is to absorb the water from the contents of the small intestine. Water is constantly being absorbed by the large intestine. There are three main parts to the large intestine: the ascending colon; transverse colon; and descending colon.

  • Ascending colon: After leaving the small intestine, that which hasn't been absorbed into the bloodstream enters the ascending colon of the large intestine.
  • Transverse colon: Bulk digested material then passes along the transverse colon, which is almost horizontal and goes from right to left.
  • Descending colon: The last part of the large intestine, bulk material then travels downwards where it is passed onto the rectum.

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Rectum: The rectum stores faeces until stretching of its walls cause its muscles to contract, and the anal sphincter (anus) relaxes to allow defaecation. 

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So, where does food go after we eat it?

After leaving the stomach, chyme, as it is now called, passes on to the duodenum. This is the first part of the small intestine. After the duodenum, the chyme enters the small intestine. Here, all the nutrients in the food (chyme) are absorbed into the bloodstream through villi. Villi are tiny finger-like projections, and they further increase the surface area available for absorption. Once the nutrients are absorbed into the bloodstream, they are distributed throughout the body.

That which remains is excess material which was unable to be absorbed into the bloodstream. Such things as cellulose (fibre) are good for you and your digestive system, however they are not absorbed into the bloodstream, and must be removed through defaecation. So the food then passes on to the ascending colon, the transverse colon, and finally the descending colon of the large intestine where the water is absorbed back into the body.

The bulk material then passes on to the rectum. Here, it is stored until the walls of the rectum are stretched. This causes its muscles to contract. The anal sphincter relaxes, and the undigested material passes out of the body.

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