The duodenum is about 25 cm (10 inches) long; the jejunum is about 2.5 m (8 feet) long and the ileum is about 3.6 m (12 feet) long. ... These are called the plicae circulares.

Light micrograph of a section through the wall of the human jejunum, part of the small intestine. The lining has many folds, known as plicae circulares or Kerckring's valves, in this region.