At approximately day 1

Normal fetal weight: 14 gm

Reference

Moore KL, Persaud TVN. 1998. The Developing Human: Clinically Oriented Embryology. 6th ed. Philadelphia: WB Saunders Co.

At approximately day 1

The small intestine elongates and the primary intestinal loop retracts into the abdominal cavity, rotating an additional 180 degrees by week 11.

Duration: 1 week

Reference

Larsen WJ. 1997. Human Embryology. New York: Churchill Livingstone Inc.

At approximately day 1

Ciliated columnar epithelium appears.

Reference [PubMed Link]

Montgomery RK, Mulberg AE, Grand RJ. 1999. Development of the human gastrointestinal tract: twenty years of progress. Gastroenterology 116(3):702-731.