Functional and morphological characteristics of venous system with special references in cardiovascular regulation

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To elucidate the mode of venous transport, we have undertaken to study regional differences in mechanical characteristics of the isolated canine veins and the principles in the distritution of venous valves. There were marked regional differences in the venous distensibility. The non-uniform distensibility of venous walls was understood in terms of local differences in the architecture of elastic fiber components and the content of smooth muscle cells in the venous walls. The largest distensibility in all isolated canine veins was observed in the hilar portal vein. Activation of venous smooth muscles in the portal vein also caused the largest reduction of the distensibility in all veins. The anatomical and functional principles in the localization of venous valves were summarized as follows: (1) In the human, monkey, dog and rabbit venous systems the valves were always observed at the positions of the venous angles and the inguinal ligaments, but (2) were not found in the superior and inferior caval veins. (3) The numbers of venous valves in the deep intramuscular veins of human and monkey legs were greater than those in dog and rabbit legs. (4) When venous valves existed, a confluence of tributaries always could be found in the upstream compartmentof the main vein. (5) The venous valves were always found at the positions where the veins were compressed by extrinsic forces produced by the movement of joints and the stretch of tendons and fasciae. Regional and spieces differences in distribution of aminergic nerve fibers in monkey, dog and rabbit veins were als investigated by use of glyoxylic acid technique. In all animals, aminergic nerve fibers with varicoses innervated most densely in abdominal caval veins and portal veins. The decreasing order of the innervation density was as follows: monkey> dog> rabbit.