中文摘要：

为了研究牦牛肺脏对高原低氧的适应性过程的结构基础，通过多种组织化学方法和透射电镜技术对1日龄、5月龄和成年牦牛肺脏显微结构和超微结构进行研究。研究发现：1日龄、5月龄和成年组牦牛肺动脉中膜肌层所占管径的比例（MT%）均较高，分别为10.71%、12.53%和11.18%；1日龄牦牛细支气管管壁已形成一层完整的平滑肌层。牦牛呼吸道杯状细胞的分泌颗粒电子密度高，在颗粒中心有低电子密度的区域；Clara细胞的分泌物是有膜包裹的致密分泌颗粒、少量致密分泌颗粒和灰白色物质混合的分泌滴。1日龄、5月龄牦牛肺动脉受低氧的影响较大，内皮细胞增殖明显，呈立方状，突入管腔呈栅状排列；平滑肌细胞肥大呈立方状、细胞器显著增多；各年龄组牦牛血-气屏障厚度均很薄，与低海拔地区大鼠接近，1日龄、5月龄和成年组厚度分别为0.445、0.506和0.423μm。以上结果表明，低氧对肺动脉内皮细胞、平滑肌细胞和细支气管平滑肌有明显的影响，这种影响在5月龄牦牛表现最为显著，但随着年龄的增长，低氧对牦牛肺脏结构的影响逐渐减弱。这种结构与年龄相关的变化表明牦牛在生长发育过程中其肺脏逐渐适应了高原低氧的环境。

英文摘要：

Histology methods and transmission electron microscope technique were used to investigate the pulmonary morphological structure and adaptive changes in one-day-old yak, five-month-old yak and adult yak. The results showed that the percentage of media muscle thickness of pulmonary artery （MT%） were thicken, the mean value of one-day-old group, five-month-old group and adult group were 10. 71%, 12.53% and 11.18%, respectively. There was a complete smooth muscle layer in bronchiole wall in one-day-old yak. In gas-conducting airways, the secretory granules of goblet cells were dense; there was sparse area in granules central. The secretory granules of Clara cells were dense secretory granules or a mixture of dense secretory granules and pale secretory droplets. In pulmonary artery, endothelial cells were cubic and proliferated, some of them intruded lumen. Smooth muscle cells are cubic, organelles increased. The thickness of blood-air barrier in yak was very thin. The thickness of blood-air barrier in different age group were 0. 445（one-day old）,0. 506（five-month old） and 0. 423（adult） μm, respectively. These results indicated that hypoxia affected the structure of lung in yak; it was significant in five-month- old group, but as the increasing of age, the affection was decreasing. The changes of structure affected with age indicate that the lung of yak has adapted to the hypoxia.