The organ that is behind the belly button is the small intestine. It is part of the body's digestive system.
Partially digested food from the stomach enters into the small intestine via the pyloric valve. The most vital part of food digestion takes place in the small intestine. Measuring approximately 21 feet in length, it is coiled loosely in the abdomen.
The small intestine is comprised of ileum, duodenum and jejunum. Food is broken down in the duodenum, the intestine's upper portion. To cater to the body's energy and health requirements, important nutrients like fats, minerals, vitamins, carbohydrates and proteins are absorbed in the jejunum and ileum. Villi, tiny finger-like projections line the small intestine, giving additional surface area and thus, better food absorption.