A vascular system consists of a supplying arterial and a draining venous part which are connected by a terminal vascular network. The arterial segment can be characterized according to the structural features of the vessel wall. However, it is sometimes difficult to distinguish the capillary from the postcapillary vessels on the basis of structural features alone. On the other hand, physiologic qualities such as permeability can hardly be associated with an equivalent histologic pattern of the vessel wall (Illig 1961; Rhodin 1967, 1968; Hauck 1971; Westergaard 1974). A definition of a vascular segment based on biologic significance should combine morphological and functional qualities of the vessel walls.
KeywordsVascular System Capillary Density Intracranial Artery Ontogenic Development Capillary Surface Area
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