Human dermal microvasculature: I. Its segmental differentiation. Light and electron microscopic study.

Light microscopic examination of I micrometer thick epoxy resin sections of human skin preserved in fixative normally used for electron microscopy allows division of the microvasculature of the reticular and superficial dermis into several distinct segments. More precise delineation of these components can be achieved by correlative study using electron microscopy. Measurement of vessel diameter in tissue sections is of limited value in vessel classification because there is a wide overlap between different vascular segments and the results are influenced by the type of fixative used for processing the tissue. Detailed observation of the morphological characteristics of the endothelium and its investment, including the elastic and basal laminae, is consider preferable for identifying individual vascular segments. Differences in body region do not appear to have any obvious influence on vessel structure although there are regional differences in vessel density and arrangement. In comparison with earlier studies on animal tissues or human skin, no structures resembling arteriovenous shunts or precapillary sphincters were observed in the present investigation. However, closed fenestrae and other structures thought to be transendothelial channels were often found at the tips of capillary loops adjacent to the epidermis.