Small intestine

The small intestine or small bowel is the part of the gastrointestinal tract between the stomach and the large intestine, and is where most of the digestion and absorption of food takes place. The small intestine has three distinct regions – the duodenum, jejunum, and ileum. The duodenum receives bile and pancreatic juice through the pancreatic duct, controlled by the sphincter of Oddi. The primary function of the small intestine is the absorption of nutrients and minerals from food.

This article is primarily about the human gastrointestinal tract. The information about its processes is directly applicable to most placental mammals. A major exception to this is the digestive process in ruminants – notably cows. In invertebrates such as worms, the term "large intestine" is often used to describe the entire gastrointestinal tract.

Structure

The average length of the small intestine in an adult human male is 6.9 m (22 ft 8 in), and 7.1 m (23 ft 4 in) in an adult female. It can vary greatly, from as short as 4.6 m (15 ft) to as long as 9.8 m (32 ft). Recent studies indicate that small intestine may be shorter, around 3.5 m (11 ft 6 in), and that the length is less affected by age after childhood than expected.