Thyroid gland approaches structural maturity.
Fisher DA. 1997. Fetal thyroid function: Diagnosis and management of fetal thyroid disorders. Clinical Obstetrics & Gynecology 40(1):16-31.
Islets develop with insulin cells in the center and glucagon, endorphin and pancreatic polypeptide cells surrounding them by week 20.
Duration: 3 weeks
Hahn von Dorsche H, Falkmer S. 2000. Ontogenesis of human islets of Langerhans. Review of light and electron microscopic data, immunohistochemical and functional data on fetal development of the endocrine pancreas. Journal of Evolutionary Biochemistry and Physiology 36(6):701-718.