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Large Intestine

The large intestine (or large bowel) is the part of the digestive system where waste products from the food you eat are collected and processed into faeces.

The large intestine is about 1.5 m long and consists of the caecum, appendix, colon and rectum - which are distributed in the abdominal cavity.

What does it do?

The large intestine performs the following functions:

  • reabsorbs water and maintains the fluid balance of the body
  • absorbs certain vitamins
  • processes undigested material (fibre)
  • stores waste before it is eliminated.

Caecum

The caecum is the first part of the large intestine. Shaped like a small pouch and located in the right lower abdomen, it is the connection between the small intestine and the colon.

What does the caecum do?

The caecum accepts and stores processed material from the small intestine and moves it towards the colon. As the processed food approaches the end of the small intestine, a valve separating the small and large intestines opens, the caecum expands and the material enters. At this stage, the mixture normally contains:

  • undigested food (fibre)
  • a little bit of water
  • some vitamins
  • some minerals or salts

Appendix

The appendix is a small projection emerging from the caecum.

In human beings, the appendix has no known function and is thought to be a remnant from a previous time in human evolution.

In some people, the appendix becomes infected or inflamed (a condition known as 'appendicitis'), and the appendix needs to be removed (via surgery).

Colon

Shaped like an inverted 'U', the colon is the longest part of the large intestine.

Where is the colon?

The colon has four sections that are located in the abdominal cavity.

  • Ascending colon - starts at the caecum at the bottom right hand side of the abdomen and ascends (ie, goes upwards) towards the liver.
  • Transverse colon - transverse means 'across'. This part of the colon extends across the abdomen from right to left.
  • Descending colon - descends (goes downwards) on the left hand side of the abdomen.
  • Sigmoid colon - it is the last part of the large intestine, and is located on the bottom left hand side of the abdomen. It is the S-shaped connection between the descending colon and the rectum.

What does the colon do?

Within the colon, the mixture of fibre, small amounts of water, and vitamins, etc, mixes with mucus and with bacteria that live in the large intestine - and starts to form faeces.

As faeces travels through the colon, the lining of the colon absorbs most of the water and some vitamins and minerals.

The bacteria in the colon chemically break down some of the fibre to produce nutrients for their own survival and to nourish the cells lining the colon. Thus, the fibre in your diet is extremely important to maintain the long-term health of the colon.

Through muscular movements of the colon, faeces is pushed along until finally, the walls of the sigmoid colon contract, causing the faeces to move into the rectum.

Rectum

The rectum is the final part of the large intestine. It is where stool (faeces) is stored before being passed as a bowel motion.

Problems/disorders of the large intestine

A number of problems could arise in large intestine - some are easily treated, while others can be more serious. Information leaflets on some conditions of the large intestine are available by clicking below.