Cytogenesis of human fetal pancreas has been studied electron microscopically. In a 10 weeks fetus, hardly any indication for differentiation of the pancreatic epithelium cells has been observed. Neither α and β granules nor zymogen granules have been found in the cytoplasm, Golgi apparatus is not well developed and rough endoplasmic (rER) reticulum was scarecely observed. The cytoplasm is filled with a large member of glycogen granules and with free polyribosomes.
In a 13 weeks fetus, differentiated exocrine cells start to appear which are characterized by well developed rER in paralell lamellar array or in whorle structure, by increased amount of Golgi membrane and by a number of zymogen granules. In a 22 weeks fetus, almost all the exocrine cells have been differentiated and the cytoplasm is filled with expanded profils of rER. In some cells rER is transformed to vesicular form and a number of zymogen granules are accumulated in the apical cytoplasm, suggesting extensive synthesis and storage of the secretory proteins,
Differentiated endocrine cells also appear around 13 weeks of gestation, and α and, β granules have been found in the fetus of 13 weeks and 18 weeks, respectively.
