At approximately day 1

Craniofacial: The face is recognizably human.

Reference

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

At approximately day 1

Cell differentiation initiated.

Reference [PubMed Link]

Fisher DA, Dussault JH, Sack J, Chopra IJ. 1976. Ontogenesis of hypothalamic-pituitary-thyroid function and metabolism in man, sheep, and rat. Recent Prog Horm Res 33:59-116.

At approximately day 1

Basophils and corticotropes present; adrenocorticotropin detected.

Reference [PubMed Link]

Kaplan SL, Grumbach MM, Aubert ML. 1976. The ontogenesis of pituitary hormones and hypothalamic factors in the human fetus: maturation of central nervous system regulation of anterior pituitary function. Recent Prog Horm Res 32:161-243.

At approximately day 1

Neural crest cells differentiate into the adrenal medulla.

Duration: 1 week

Reference

Nussey SS, Whitehead SA. 2001. Endocrinology: An Integrated Approach. Oxford, UK: BIOS Scientific Publishers, Ltd.

At approximately day 1

Lateral and posterior areas begin to differentiate; dorsomedial nucleus is well defined; medial preoptic nucleus and medial mamillary body can be identified; hypothalamic sulcus is an obvious feature of the ventricular wall.

Duration: 1 week

Reference [PubMed Link]

Koutcherov Y, Mai JK, Paxinos G. 2003 Dec. Hypothalamus of the human fetus. J Chem Neuroanat 26(4):253-70.

At approximately day 1

Inferior parathyroid glands disconnect from the pharynx and migrate down to the neck with the thymus; superior glands attach to the dorsal part of the thyroid.

Reference

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

At approximately day 1

Craniofacial: Lateral palatal shelves elongate and ascend, gradually fusing together.

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

Craniofacial: Paired cartilages of the chondrocranium begin to fuse.

Duration: 5 weeks

Reference

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

At approximately day 1

Limbs: Limbs rotate in opposite directions

Reference

Sadler TW. 2004. Langman’s Medical Embryology. Ninth Edition. Maryland: Lippincott Williams & Wilkins.

At approximately day 3

Thyroid gland descends to lower part of neck.

Duration: 1 week

Reference [PubMed Link]

Fisher DA, Dussault JH, Sack J, Chopra IJ. 1976. Ontogenesis of hypothalamic-pituitary-thyroid function and metabolism in man, sheep, and rat. Recent Prog Horm Res 33:59-116.

At approximately day 3

Tubular structures visible containing insulin-immunoreactive epithelial cells.

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.

At approximately day 5

Small intracellular canaliculi develop into colloid material then into organized follicles by week 12.3.

Duration: 5 weeks

Reference [PubMed Link]

Fisher DA, Dussault JH, Sack J, Chopra IJ. 1976. Ontogenesis of hypothalamic-pituitary-thyroid function and metabolism in man, sheep, and rat. Recent Prog Horm Res 33:59-116.

At approximately day 7

Limbs: Cell death leads to separation of digits.

Duration: 1 week

Reference

Sadler TW. 2004. Langman’s Medical Embryology. Ninth Edition. Maryland: Lippincott Williams & Wilkins.