The primary function of the small intestine is to continue the process of digestion that began in the mouth and the stomach. The small intestine absorbs water and nutrients, and it prepares the food for the next step in digestion, the large intestine.
In the small intestine, partially digested food, which has been reduced to a slurry called chyme, is mixed with intestinal juices and pancreatic juice, which contains the enzymes amylase, trypsin and lipase. Trypsin continues to break down proteins, amylase changes starches into simple sugars, and lipase divides fats into fatty acids and glycerin. Bile from the liver is also added to help break down fats. Bile and pancreatic juice are delivered through the hepatopancreatic duct. Peristalsis, which is the contractions that move food through the digestive system, helps to mix these juices and enzymes in the small intestine.
The small intestine is lined with tiny projections called villi and microvilli. These projections are specialized to absorb different types of nutrients, which are then released into the blood stream to provide fuel for the body. After this, the digested food is moved into the large intestine, or colon.
The small intestine is a long organ that's divided into the duodenum, which is connected to the stomach, jejunum and ileum. The average small intestine is about 22 feet long.