At approximately day 1

Thyrotropes (which produce TSH) present.

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

Gonadotropes for FSH present.

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

Lateral tuberal nucleus becomes visible; fornix continues to mature; intermediate nucleus is well defined; mammillary complex is well-differentiated by week 15.

Duration: 2 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

Craniofacial: Ossification of the skull begins, following a defined sequence.

Reference

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

At approximately day 1

Primitive islet structures express all four pancreatic hormones (insulin, glucagon, somatostatin, and pancreatic polypeptide).

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 1

Fetal zone cells show immunostaining for human growth hormone receptors.

Duration: 1 week

Reference [PubMed Link]

Simard M, Manthos H, Giaid A, Lefebvre Y, Goodyer CG. 1996 Aug. Ontogeny of growth hormone receptors in human tissues: an immunohistochemical study. J Clin Endocrinol Metab 81(8):3097-102.