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The bowel is part of the lower gastrointestinal tract, which is part of the digestive system. The digestive system starts at the mouth and ends at the anus. It helps the body break down food and turn it into energy. It also gets rid of the parts of food the body does not use.
The small bowel (small intestine)
This is a long tube (4–6 m) that absorbs nutrients from food. It is longer but narrower than the large bowel. It has three parts:
- duodenum – the first section of the small bowel; receives broken-down food from the stomach
- jejunum – the middle section of the small bowel
- ileum – the final and longest section of the small bowel; transfers waste matter to the large bowel.
The large bowel (large intestine)
This tube is about 1.5 m long. It absorbs water and salts, and turns what is left over into solid waste matter (known as faeces, stools or poo when it leaves the body). The large bowel has three parts:
- caecum – a pouch that receives waste from the small bowel; the appendix is a small tube hanging off the end of the caecum
- colon – the main working area of the large bowel, the colon takes up most of the large bowel’s length and has four parts: ascending colon, transverse colon, descending colon and sigmoid colon
- rectum – the last 15–20 cm of the large bowel.
This is the opening at the end of the bowel. During a bowel movement, the anal muscles relax to release faeces. Anal cancer is treated differently to bowel cancer.
The lower digestive system
Understanding Bowel CancerDownload resource
This information is reviewed by
This information was last reviewed January 2021 by the following expert content reviewers: A/Prof David A Clark, Colorectal Surgeon, Royal Brisbane and Women’s Hospital, and The University of Queensland, QLD, and The University of Sydney, NSW; A/Prof Siddhartha Baxi, Radiation Oncologist and Medical Director, GenesisCare Gold Coast, QLD; Dr Hooi Ee, Specialist Gastroenterologist and Head, Department of Gastroenterology, Sir Charles Gairdner Hospital, WA; Annie Harvey, Consumer; A/Prof Louise Nott, Medical Oncologist, Icon Cancer Centre, Hobart, TAS; Caley Schnaid, Accredited Practising Dietitian, GenesisCare, St Leonards and Frenchs Forest, NSW; Chris Sibthorpe, 13 11 20 Consultant, Cancer Council Queensland; Dr Alina Stoita, Gastroenterologist and Hepatologist, St Vincent’s Hospital Sydney, NSW; Catherine Trevaskis, Gastrointestinal Cancer Specialist Nurse, Canberra Hospital, ACT; Richard Vallance, Consumer.