Development of Human Embryonic and Fetal Dermal Vasculature.

Abstract

This report summarizes recent advances in the understanding of the structure and organization of the microvasculature in developing human skin. Previous observations suggested that the skin contains no blood vessels as late as eight weeks estimated gestational age (EGA). Computer reconstructions, in conjunction with light and transmission electron microscopy (TEM), however, demonstrated that specimens as young as 35-45 d show a level of vascular complexity previously unknown. The computer reconstructions showed that the vasculature was organized in one or two planes parallel to the epidermis. A simple, single plane was evident in specimens 40-50 d EGA, whereas specimens 50-75 d EGA showed two planes. Fewer vessels were continuous throughout the tissue sample in the younger specimens compared with the older specimens. Superior views highlighted the continuities and connections of vessels. The younger specimens showed more discontinuous segments of vessels when compared with the network established in the older specimens. In the earliest specimens examined morphologically (35-40 d), simple, capillarylike vessels were morphologically identifiable in presumptive dermis. The samples studied by TEM revealed detailed structure of the vessel wall including extreme attenuations and projections, plasmalemmal vesicles, and junctions similar to adult endothelial cells. Little or no basal lamina surrounded the vessel. The basal lamina first appeared in the form of amorphous deposits and eventually thickened and became continuous. By the end of the first trimester, the basal lamina still lacked the organization of adult cutaneous arterial and venous segments. These findings suggest that the major vascular organization of the dermis is defined in the first trimester of development.

Dermal Contributions to Human Interfollicular Epidermal Architecture and Self-Renewal

“…Given the important functional basis for the organisation of the dermal vasculature, it is likely that cues from the vasculature help to establish the architecture of the epidermal-dermal interface. The pattern of dermal capillaries emerges early during embryogenesis coincident with the development of the epidermis [ 35 , 36 , 37 ]. By birth, the skin possesses a mature capillary architecture; however, little is known about the mechanisms by which the epidermis organises around the capillaries to achieve this state.…”

Fish Scales Dictate the Pattern of Adult Skin Innervation and Vascularization

“…The vertebrate skin undergoes dramatic changes as animals develop from embryonic to adult stages. The epidermis grows from a simple mono- or bilayered epithelium to a stratified multi-layer epithelium, dermal vasculature elaborates, specialized sensory structures and dermal appendages appear, and the skin area greatly expands (Jenkins and Lumpkin, 2017; Johnson and Holbrook, 1989; Munger and Ide, 1988). How these events are coordinated, and how nerves and blood vessels remodel to accommodate these dramatic changes in the skin, has not been well characterized.…”

Fetal Kidney Transplantation for In Utero Fetuses

“…ECM is known to promote development and angiogenesis in kidney organoids that mimic embryonic organs 27). Additionally, some components of ECM have been reported to play a role in directing the migration of endothelial cells, contributing to angiogenesis 28). Thus, an analysis focusing on the unique ECM composition of the fetal subcutaneous space is necessary in the future to understand the difference between adult and fetal subcutaneous transplantation.…”