The first part of the small intestine is called the duodenum. The duodenum is only 25 cm long, but most of the digestion takes place in this region.

Small amounts of chyme are ejected approximately every 20 seconds from the stomach into the duodenum.

Also opening into the duodenum are ducts from the pancreas and the gall bladder. These allow enzyme-rich pancreatic juice and bile to be released and mixed with the chyme.

Chemical breakdown of carbohydrate, protein and fats into smaller absorbable molecules takes place.

Peristaltic waves of muscular contraction mix and move the chyme down the duodenum and into the jejunum, measuring about 2.5 m long.

Peristaltic waves of muscular contraction move the chyme through the jejunum until it reaches the ileum.

The jejunum has a huge surface area created by finger-like structures called villi. These assist with the absorption of nutrients into the bloodstream.

Villi play an important role in absorbing the breakdown products of digestion. The increase in surface area, allows for ready absorption of these products of digestion.

With villi Flat surface Nutrients to bloodstream

Each villus has a rich blood supply, allowing nutrients to be readily absorbed and transported to the liver. A lacteal is also present; absorbing fat nutrients and carrying them to the circulatory system.