Thyrotropin-releasing hormone and luteinizing hormone-releasing hormone present.
Winters AJ, Eskay RL, Porter JC. 1974. Concentration and distribution of TRH and LRH in the human fetal brain. Journal of Clinical Endocrinology & Metabolism 39(5):960-963.
Thyroid-stimulating hormone (TSH) detected.
Duration: 2 weeks
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.
Differentiation of the thyroid gland occurs.
Duration: 1 week
Sadler TW. 2000. Susceptible periods during embryogenesis of the heart and endocrine glands. Environ Health Perspect 108 (suppl 3):555-561.
Skeletal: Ossification becomes evident in the vertebral arches and continues through 25 years of age
Moore KL, Persaud TVN. 1998. The Developing Human: Clinically Oriented Embryology. 6th ed. Philadelphia: WB Saunders Co.
Definitive erythroblasts enter the bloodstream and gradually outnumber circulating primitive erythroblasts.
Duration: 30 weeks
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
Craniofacial: Most membrane bones of skull are present.
O’Rahilly R, Muller F. 2001. Human embryology & teratology. Third edition. New York: Wiley-Liss.
Glucagon and somatostatin are expressed in isolated epithelial cells, and insulin expressing cells are clustered and more prevalent.
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.