The small intestine is a pink tube-shaped organ lined with muscle. It is about 20 feet long on average (can vary from 15 to 30 feet) and about one inch in diameter. The top is connected to the stomach and the bottom is attached to the large intestine. To move food along, the intestines normally contract about a dozen times a minute. Digestion begins by chewing and breakdown in the stomach, but the majority of further digestion and nutrient absorption occurs in the small intestine where various additional enzymes that break down nutrients are introduced.