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

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Abstract
Light microscopy of 1 .mu.m thick epoxy resin sections of human skin preserved in fixative normally used for EM allowed division of the microvasculature of the reticular and superficial dermis into several distinct segments. More precise delineation of these components was achieved by correlative study using EM. Measurement of vessel diameter in tissue sections was of limited value in vessel classification because there was a wide overlap between different vascular segments and results were 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, was considered preferable for identifying individual vascular segments. Differences in body region did not appear to have any obvious influence on vessel structure although there were 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. Closed fenestrae and other structures thought to be transendothelial channels were found at the tips of capillary loops adjacent to the epidermis.