Dermis: Organization and Matrix Weeks 14-17

Elastic fibres are formed

Elastic fibers are first seen in the reticular dermis in the 14th - 17th weeks of gestation and in the papillar dermis in the 36th week of gestation. The elastic fiber network is not fully mature until about 2 years after birth.

This transmission electron micrograph taken of human skin at 14-17 weeks EGA clearly shows the microfibrillar component of elastin. The top of the picture shows a basal keratinocyte resting on the dermal-epidermal junction (DEJ). Can you identify the lamina licida and the lamina densa? The banded fibrils are collagen. Can you identify a structure composed of type VII collagen? Hint: look for the arrowhead. The elastin microfibrillar component is seen as a group of fibrils running diagonally across the image (arrows).