General Anatomy/Gastrointestinal System/Small Intestine

In biology the small intestine is the part of the gastrointestinal tract (gut) between the stomach and the large intestine and includes the duodenum, jejunum, and the ileum. It is where the vast majority of digestion takes place.

Size and sections In humans over 5 years old it is approximately 7 m (21 ft) long and can vary from 4–7 m (13.12-22.97 ft).

It is divided into three structural parts:


 * duodenum 25 cm (9.84 in) in length
 * jejunum 2.5 m (8.2 ft)
 * ileum 3.5 m (11.5 ft)

Although the small intestine is much longer than the large intestine (typically 4-5 times longer), it is referred to as such due to its comparatively smaller diameter. On average, the diameter of the small intestine of an adult human measures approximately 2.5–3 cm, and the large intestine measures about 7.6 cm in diameter.