In humans, the small intestine is about 20 feet long, and the large intestine is about 5 feet long. Both are situated in the abdomen and form a continuous tube from the stomach to the anus.
The small intestine is about an inch in diameter. It is made up of three sections called the duodenum, the jejunum and the ileum. The primary function of the small intestine is to absorb nutrients from digested food through the intestinal wall, allowing them to enter the bloodstream. The large intestine, also called the colon, is about 3 inches in diameter. Its function is to absorb water from the waste products of the digestive process, creating stool.