[Structures ensuring blood flow control in the vessels of microcirculatory bed]

The aim of this study was to investigate the morpho-functional mechanisms of blood flow regulation in the vessels of the microcirculatory bed in various organs of man and animals (rabbitts and dogs). Ranvier's and Rasskazova's methods of silver nitrate impregnation, histological section staining with hematoxylin-eosin and after van Gieson, Gomori's method for demonstration of acid and alkaline phosphomonoesterases were used to detect the presence of the structures within the vessels of the microcirculatory bed that are capable of changing the blood flow through their lumen. These mechanisms can be temporary, and their activity is associated with the functional state of the endothelium (presence of microprojections, endotheliocyte swelling, changes of endotheliocyte orientation and laminar surface size). Permanent structures are located in microvessel walls (sphincters) and they possess high activity of acid and alkaline phosphomonoesterses. Arteriolar-venular anostomoses, direct transition of arterioles into the venules and peculiarities of microvessel branching are also attributed to the mechanisms of blood redistribution. Under pathological conditions some additional structures may develop that include polyp-like structures in capillaries and venules, intimal cushions, ampule-like expansions of the arterioles, varicose widening of venular orifices and vascular glomeruli.