Ellis C G, Mathieu-Costello O, Potter R F, MacDonald I C, Groom A C
Department of Medical Biophysics, University of Western Ontario, London, Canada.
Microvasc Res. 1990 Jul;40(1):63-72. doi: 10.1016/0026-2862(90)90008-f.
It is generally assumed that when a muscle is shortened or extended the total length of capillaries does not change, implying that capillaries are nondistensible, longitudinally. On the basis of stereological estimates of capillary anisotropy versus sarcomere length, we propose that as long as capillaries are in a tortuous configuration muscle extension will merely decrease the tortuosity, leaving vessel length unaltered. Once capillaries have been pulled into a straight configuration, further extension of the muscle will cause the vessels to stretch. By means of intravital videomicroscopy we have demonstrated that stretching of individual capillaries does indeed occur over a sarcomere length range of 2.1 to 2.9 microns in rat extensor digitorum longus muscle. In vivo measurements of the lengths of six capillaries together with the sarcomere lengths of adjacent fibers were made in muscles positioned at various degrees of extension. Normalized data indicated that four capillaries stretched to the same degree as the muscle, one stretched more and another less. This may reflect differences in distensibility or tortuosity of capillaries in series with one another. The elastic stretching of capillaries during muscle activity may have important consequences in terms of shifts in permeability and increases in capillary surface area.
一般认为，当肌肉缩短或伸展时，毛细血管的总长度不变，这意味着毛细血管在纵向是不可伸展的。基于毛细血管各向异性与肌节长度的体视学估计，我们提出，只要毛细血管呈曲折形态，肌肉伸展只会降低曲折度，而血管长度不变。一旦毛细血管被拉成直线形态，肌肉的进一步伸展将导致血管拉伸。通过活体显微镜观察，我们已经证明，在大鼠趾长伸肌中，单个毛细血管在2.1至2.9微米的肌节长度范围内确实会发生拉伸。在处于不同伸展程度的肌肉中，对六条毛细血管的长度以及相邻纤维的肌节长度进行了体内测量。标准化数据表明，四条毛细血管与肌肉伸展程度相同，一条伸展程度更大，另一条更小。这可能反映了相互串联的毛细血管在可伸展性或曲折度上的差异。肌肉活动期间毛细血管的弹性拉伸可能在通透性变化和毛细血管表面积增加方面产生重要影响。
