THE CUTANEOUS MICROCIRCULATION - ULTRASTRUCTURE AND MICROANATOMICAL ORGANIZATION

The cutaneous microcirculation is organized as two horizontal plexuses . One is situated 1-1.5 mm below the skin surface, and the other is at the dermal-subcutaneous junction. Ascending arterioles and descending venules are paired as they connect the two plexuses. From the upper l ayer. arterial capillaries arise to form the dermal papillary loops th at represent the nutritive component of the skin circulation. There ar e sphincter-like smooth muscle cells at the point where the ascending arterioles divide to form tile arteriolar component of the upper horiz ontal plexus. At the dermal subcutaneous junction, there are collectin g veins with 2-cusped valves that are oriented to prevent the retrogra de flow of blood. Laser Doppler flowmetry (LDF) has demonstrated vasom otion of red cell flux localized to the sites of ascending arterioles. The simultaneous recording by LDF of red cell flux and the concentrat ion of moving red blood cells from individual sites allows one to cons truct by computer topographic maps of these tno valves. The two maps, based on initial studies using correlative shin biopsy specimens. can define 1-mm(3) volumes of skin that are predominantly arteriolar in co mposition, predominantly venular in composition, or essentially devoid of all microvascular elements. The electron and light microscopic fea tures that define the microvascular segments: when coupled with the ab ility of LDF to define the predominant microvascular segments under th e probe, will allow one to study both tile mechanisms of normal physio logical states and the pathogenetic mechanisms underlying pathological skin disorders in which the microvasculature plays a predominant role .