Schematic representation of developing human epidermis. (a) Two cell layers, peridermal cells and basal cells at the first trimester (8 weeks). (b) Three cell layers at 11 weeks. The periderm cells become elevated. (c) By 21–24 weeks all the cell layers of mature epidermis are present. Tight junctions are shown in blue, desmosomes in red, adherens junctions in yellow, and green indicates gap junctions. The density of junctions increases during the maturation.
