At approximately day 1

Eosinophiles visible.

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

Fornix is visible; ventromedial hypothalamus is well defined; anlage of the paraventricular nucleus is apparent.

Duration: 3 weeks

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

Skeletal: Three primary ossification centers of the vertebrae are present.

Reference

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

At approximately day 1

Craniofacial: Palatal shelves fuse with the nasal septum.

Duration: 3 weeks

Reference

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

At approximately day 1

Limbs: Ossification of the bones of the extremities begins

Reference

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

At approximately day 5

Growth hormone (GH), follicle-stimulating hormone (FSH), luteinizing hormone (LH) and low levels of prolactin 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.