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This book presents an overview of a new group of progenitor stem cells. Their origins were originally detected in light- and electron microscopical sections of plastic embedded human embryonal and fetal organs.

The distribution of these cells can result in a large quantity of ectopic stem cells. The observation of these ectopic stem cells leads us to postulate the existence of a basic wave of stem cell progenitors. This process proceeds earlier and independently from germ cell migration. This first wave of progenitor stem cell migration initially reaches the peri-aortal AMG-region (Aortal-Mesonephric-Gonadal region). From here, some of these progenitor cells enter the aorta, are distributed through the vascular system and become the embryonal stem cells (reserve cells) in many peripheral tissues. A second part delivers progenitor cells for the adrenal 'anlage'. Within the peripheral Zona definitiva of the adrenal cortex the progenitor cells multiplicate and subsequently leave the adrenal cortex through a gate of the capsule. The progenitor cells arrive at the pre-aortal sympathic plexus ('second brain'). Within the plexus ganglia they form new organ-like clusters, the paraganglia. In a second process the progenitor cells (Chromaffine cells) enter sympathetic nerve bundles. Here an 'axonal migration' starts, which guides the progenitor cells to several peripheral organs. During this migration process the stem cells develop into their final state. In the adrenal cortex the ingrowing nerves guide the stem cells to the adrenal medulla. In the pancreas the ingrowing nerve fibers guide the stem cells to the islets.

These newly detected stem cells represent a specific developmental step which is found only in humans.