Scanning and transmission electron microscope study on the terminal blood vessels of the rat skin.

The microvasculature in the subepidermal layer of the rat foot was examined by scanning electron microscopy of corrosion casts and by transmission electron microscopy of serial ultrathin sections. Three-dimensional observation of the casts demonstrated that, in the walking pads (pressure areas) with a thick epidermis, terminal vessels formed tortuous capillary loops that penetrated vertically into well-developed dermal papillae. In other regions of the foot (non-pressure areas) with a thin epidermis, terminal vessels formed a horizontally arranged capillary network and each capillary of the network fitted into a shallow groove along the dermal epidermal boundary base. These differences in the pattern of vascular distribution might be of significance from the view point of the blood flow; in pressure areas, the vertically arranged, tortuous vessels might allow vertical mobility of the skin without injury to them and might keep the blood flow normal against the force of compression. In thin sections, however, capillaries of both the loops and networks were similar in spite of the differences in the vascular distribution and the architecture of the epidermal-dermal junction. Vessels located in close proximity to the epidermis exhibited endothelial fenestrations along their proximal margins. In vessels away from the epidermis, on the contrary, fenestrations were not apparent. Since endothelial fenestration is an anatomical property related to rapid material exchange, it may be concluded that the pattern of distribution and the fine structure of subepidermal capillaries adjusts to the metabolic needs of the epidermis.