The small intestine is that portion of the digestive tract extending from the duodenojejunal junction to its termination at the ileocaecal valve which is the start of the large intestine. The total length of this tube-like structure is about six metres and it consists of two parts, the jejunum and the ileum. The jejunum is the more proximal part and passes imperceptibly into the ileum which forms the distal half of the small intestine. Both parts are mobile within the abdominal cavity, being attached to the posterior abdominal wall by a curtain of tissue called the mesentery. The ileum terminates distally in the ileocaecal valve where the small intestine enters the caecum, the first part of the large intestine or colon.