Phases in the early development of the human islet organ.

The study included morphometric examination and biochemical investigation of 41 human pancreata taken from 14th to 26th weeks of fetal development. 3 phases of development were observed. Phase I (weeks 14 to 16) is characterized by the presence of mainly islet buds. They were originated from the ducts and are vascularized during week 16. During phase II (17th to 20th weeks) the islet buds were detached from the ducts and they formed new mantled islets with the B cells in the centre. Non-B cells are situated on the periphery around the insulin producing cells. Phase III lasts from week 21 to week 26. During this phase B cells and non-B cells become more irregularly positioned within the islet, a cytology, which is similar approximating that of as also found in adult human islets. The changes of islet structure during pancreatic development are accompanied by other typical phenomena: Islet size increases during phases I and II, but decreases again during phase III. The proportion of isolated B cells outside of the islets varies during this stage of fetal development, but they generally account for about 15% of the total islet organ. This should be taken into account when assessing the islet function De Pablo et al. (1985) on a morphological basis.