Pohl U, De Wit C, Gloe T
Institute of Physiology, Ludwig-Maximilians-University Munich, Germany.
Acta Physiol Scand. 2000 Apr;168(4):505-10. doi: 10.1046/j.1365-201x.2000.00702.x.
Although it is generally assumed that small arterioles form the major site of vascular resistance, microcirculatory studies revealed that 40-55% of the total network resistance can reside in large arterioles and small arteries. Thus, the mechanisms that control smooth muscle tone in these vessels have a major impact on the overall conductance of the vascular network. These control mechanisms are different from those in small arterioles: Aside from an apparently reduced sensitivity to metabolites, the large resistance vessels are normally too far away from the capillary areas which they feed to be reached by diffusing metabolites from dependent cells within a reasonable period of time. Rather, recent intravital microscopic studies suggest that large resistance vessels are under tight control of endothelial factors such as nitric oxide and endothelium-derived hyperpolarising factor (EDHF). Nitric oxide opposes myogenic constrictions of large arterioles that potentially would impair tissue perfusion and oxygenation. Moreover, nitric oxide and EDHF play an important role in the co-ordination of large and small resistance vessel behaviour that is pivotal for the adaptation of blood flow to altered tissue oxygen demands.
尽管通常认为小动脉是血管阻力的主要部位，但微循环研究表明，总网络阻力的40%-55%可能存在于大动脉和小动脉中。因此，控制这些血管平滑肌张力的机制对血管网络的整体传导性有重大影响。这些控制机制与小动脉中的不同：除了对代谢物的敏感性明显降低外，大阻力血管通常离它们所供血的毛细血管区域太远，以至于在合理时间内依赖细胞扩散的代谢物无法到达。相反，最近的活体显微镜研究表明，大阻力血管受到内皮因子如一氧化氮和内皮衍生超极化因子（EDHF）的严格控制。一氧化氮可对抗大动脉的肌源性收缩，这种收缩可能会损害组织灌注和氧合。此外，一氧化氮和EDHF在协调大、小阻力血管的行为中起重要作用，这对于使血流适应组织氧需求的变化至关重要。
