The digestive tract

At around 9 metres long, the digestive tract stretches from the mouth to the anus. It’s divided into different sections and each section processes food in a specific way to prepare it for the next stage in digestion.

How the digestive tract works
When we swallow food, it passes through the pharynx into the oesophagus. The oesophagus contracts, gradually forcing the food down into the stomach, where a mixture of saliva and stomach acids creates a semi-liquid mass. The food mass then continues to the small intestine.

The small intestine
The small intestine, or ileum, is seven-eight metres long and digests and absorbs fats, carbohydrates and proteins. It’s divided into three sections: the duodenum, jejunum and ileum.

The small intestine uses enzymes and other secretions to digest food and absorb nutrients. The first part of the small intestine, the duodenum, is 25-30 cm long. In the duodenum, enzymes break down fats, carbohydrates and proteins, while bile emulsifies fat to help digestion and absorption. From the duodenum, the food mass continues to the jejunum, which makes up two fifths of the small intestine’s total length. The food mass then passes to the ileum, the final three fifths of the small intestine.

Nutrients are absorbed through the mucous membrane of the small intestinal wall. Made up of million of finger-like protrusions (villi), this membrane has a very large surface area – around 250 m2. This ensures a maximum absorption of nutrients from food.

The large intestine
Contractions in the wall of the small intestine (called peristalsis) force the food mass into the last section of the digestive tract, the large intestine (also called the colon). Around 1.5 metres long, the colon is divided into five main sections: the ascending colon, transverse colon, descending colon, sigmoid colon (S-shaped colon), and the rectum.

The colon absorbs water and fluids from the food and forms faeces. The colon reduces the mass of faeces, making it more solid and easier to pass.

The newly formed faeces collect in the sigmoid colon. When this part of the colon is full, the food mass begins to sink into the rectum (12 cm long).  A swelling of the rectal wall triggers a natural urge to defecate, and when the sphincter is relaxed the food mass exits the intestinal tract as faeces.

Find out more
This information is taken from a comprehensive textbook (also available as a CD-ROM) about basic stoma care.