[Microvascular anatomy of the skin and its appendages]

The microcirculatory bed of the skin has traditionally been divided into small arteries, precapillary arterioles, capillaries and venules. Also the most recent classification emphasize that the blood supply of the human dermis is a microcirculatory bed. Therefore, considering for example the skin of the lower limbs, there are too much anatomic and topographic peculiarities of the skin and subcutaneous tissue, so that a generalization of the microcirculatory patterns appears to be illusory and misleading. In fact, the foots plant is a "special microcirculatory region", and so the finger tips and the nail beds. Rich on arterio-venous anastomoses, on endoarterious blocking devices regulating the capillary blood flow, this "microcirculatory region" is characterized by haemodynamic patterns which are not comparables with those of other regions where AVA or other "special vessels" are absent. The microangiotectonic, i.e. the distribution in the tridimensional space of the dermis, adipose tissue and muscle of the smallest blood vessels show relevant differences in the foots, legs, knees or thighs. Normally, it is admitted that the majority of the papillary dermal vessels are postcapillary venules, but the ultrastructure of the arterioles and venules in the mid and lower dermis differs from the ultrastructure of comparable vessels of the deeper layers or of the subcutaneous fat. For these reason and on the basis of bioptic specimens of the skin, adipose tissue and muscles of the whole lower limbs, the subdivision in "microcirculatory regions" is proposed. The criteria are the presence or absence of AVA, the structure and localization of the endoarterious blocking devices, the structure of valve-containing venules and the microvessels-tissue relationship. Computerized Laser-Doppler Flowmetry and infra red Photo-Pulse Plethysmography, computerized Telethermography with physical stimulations, High Performance Contact Thermography and continuous registration of the skin temperature associated with pharmacological vasoactive stimulation, are helpful to identify and characterize functionally the "microcirculatory regions" of the lower limbs.