At approximately day 1

Nephrons (definitive urine-forming units) begin to form from the metanephric blastema, increasing in number to approximately 1 million per kidney at birth (presumed complete).

Duration: 32 weeks

Reference

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

At approximately day 1

Circular muscle is present in esophagus.

Reference [PubMed Link]

Mitsui T, Sugiyama N, Maeda S, Tohyama C, Arita J. 2006. Perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin suppresses contextual fear conditioning-accompanied activation of cyclic AMP response element-binding protein in the hippocampal CA1 region of male rats. Neurosci Lett 398(3):206-210.

At approximately day 4

Parenchymal and bile duct cells show immunostaining for human growth hormone receptors.

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.

At approximately day 4

Kidney tissues show positive 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.

At approximately day 4

Smooth muscle layers of the intestinal wall 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.