The Small Intestine

The small intestine is an organ located within the gastrointestinal tract. It is approximately 6.5m long in the average person and is where most of the end absorption of nutrients and minerals from food takes place. It lies between the stomach and large intestine and receives bile and pancreatic juices through the pancreatic duct, to aid digestion.

Absorption refers to the movement of nutrients, water and electrolytes from the lumen of the small intestine into the cell, then into the blood. Food components such as carbohydrates, protein and lipids are all digested differently as they require different enzymes in order to be broken down into simpler forms. They are then absorbed in the epithelial cells of the small intestine, where they proceed to enter the bloodstream or lymphatics.

The small intestine contains modifications to aid its function in the absorption of food. The mucosa and submucosa form large folds and contain microvilli, to increase the surface area, enabling for efficient absorption. The small intestine receives secretory products from other abdominal viscera, including bile, pancreatic enzymes and alkaline juice, which are vital for digestion.

In this section, learn more about the physiology of the small intestine- the process of digestion and absorption, and the histology and cellular function of the small intestine.