At approximately day 1

Craniofacial: Frontonasal prominence is clearly visible.

Reference

O’Rahilly R, Muller F. 2001. Human embryology & teratology. Third edition. New York: Wiley-Liss.

At approximately day 1

Development of fetal cortex from mesoderm is initiated. Epithelial cells from urogenital ridge proliferate and penetrate the mesenchyme.

Reference [PubMed Link]

Sadler TW. 2000. Susceptible periods during embryogenesis of the heart and endocrine glands. Environ Health Perspect 108 (suppl 3):555-561.

At approximately day 1

Hypophysial pouch elongates, detaching from the oral epithelium by week 6.

Duration: 1 week

Reference

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

At approximately day 1

Epithelium of the dorsal parts of the 3rd and 4th pharyngeal pouches proliferates and forms small nodules.

Reference

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

At approximately day 1

Skeletal: Cartilage develops from mesenchyme.

Reference

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

At approximately day 1

Yolk sac is replaced by the fetal liver as the main hemopoietic site.

Duration: 1 week

Reference [PubMed Link]

Migliaccio G, Migliaccio AR, Petti S, Mavilio F, Russo G, Lazzaro D, Testa U, Marinucci M, Peschle C. 1986. Human embryonic hemopoiesis. Kinetics of progenitors and precursors underlying the yolk sac----liver transition. The Journal of Clinical Investigation 78(1):51-60

At approximately day 3

Second hepatic colonization of hematopoietic stem cells.

Reference [PubMed Link]

Baron MH, Isern J, Fraser ST. 2012. The embryonic origins of erythropoiesis in mammals. Blood 119(21):4828-4837.

At approximately day 5

Skeletal: All ribs are present in mesenchyme.

Reference

O’Rahilly R, Muller F. 2001. Human embryology & teratology. Third edition. New York: Wiley-Liss.

At approximately day 7

Craniofacial: Development of the primary and secondary palate begins.

Duration: 7 weeks

Reference

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

At approximately day 7

Dorsal and ventral buds extend into surrounding mesenchyme, rotate around the duodenal loop and fuse by week 8.

Duration: 3 weeks

Reference [PubMed Link]

Piper K, Brickwood S, Turnpenny LW, Cameron IT, Ball SG, Wilson DI, Hanley NA. 2004 Apr. Beta cell differentiation during early human pancreas development. J Endocrinol 181(1):11-23.