The small intestine is the longest part of the digestive system.
The length of the small intestine is 7 meters (22 feet).
The main functions of the small intestine are to complete the digestion of food and to absorb nutrients.
Passage of food through the small intestine normally takes three to six hours.
Bile, pancreatic enzymes, and alkaline juice (HCO3–) are the three main substances that are received by the small intestine.
The small intestine is good for absorption since it has a large inner surface area.
This is formed due to the plicae circulares which project many tiny finger-like structures of tissue called villi. The individual epithelial cells also have finger-like projections, which are called known microvilli.
Approximately 80% of water is absorbed by the small intestine, 10% of water is absorbed by the large intestine and the remaining 10% excreted in the faeces.
The small intestine is divided into the duodenum, jejunum, and ileum.
Iron is absorbed in the duodenum, most are absorbed in the jejunum and Vitamin B12 and bile salts are absorbed in the latter part of the ileum.