Study On The Construction Characteristics Of Pulmonary Microvasculature In Yak Of Different Ages And Adult Cattle

The construction characteristics of pulmonary microvasculature in 180-day old yak, the adult yak (Bos grunniens) and the adult cattle (Bos Taurus) were studied using the technology of vascular corrosion cast and scanning electron microscopy, and compared with that of one-day old yak in a systematic way. The results showed that there were particular characters of construction of pulmonary microvasculature in yak of different ages themselves, as well as shared lots of common characteristics, and a lot of similarities and differences of the construction of pulmonary microvascular patterns were found between the adult yak and the adult cattle.The pleural surface of lung in 180-day old yak had double-layered vascular networks in density in varying degrees. The pleural superficial microvascular networks were much sparser than deep layer on the pleural surface. The superficial blood vessels could cross two or more pulmonary lobules, and the pleural superficial blood vessels and the interlobular blood vessels were mutual transitional. The outlines of lobules composed of vascular networks were various in size and form, and the lobular septa were also different in depth. The subpleural arterioles could be divided into arteriole, terminal arteriole, precapillary arteriole and capillary in turn according to the branching sequence of themselves. The plate-like, sieve-like and web-like vascular networks occurred in the subpleural microvascular networks. The outline of alveolus, alveolar sac, alveolar duct and respiratory bronchiole and terminal bronchiole, which made of microvascular networks, could be found in the cut surface at a low magnification. The pulmonary alveolar capillaries were collected into the postcapillary venule, collecting venule, and venule in turn in the pulmonary parenchyma. The pleural superficial blood vessels were smooth, while the circular and oblique constrictions of smooth muscle cells occurred on the surface of the subpleural arteriole, venule and parenchymal venule. The round imprints of endothelial nuclei were found on the cast surface of the arteriole and venule.The pleural double-layered vascular networks were also found in the lung of adult yak. The vessels from the lung parenchyma branched into the pleural superficial vessels, the interlobular vessels and the subpleural microvessels. The subpleural arterioles also could be divided into arteriole, terminal arteriole, precapillary arteriole and capillary in turn. Most subpleural capillary meshes were web-like, and also the small holes and sieve-like meshes occurred in the subpleural microvascular networks. The interlobular blood vessels and the superficial blood vessels were mutual transitional. The honeycomb vascular networks were various in size and form at a low magnification. The venule connected with the pulmonary capillary networks directly. In some fields of view, the pulmonary alveolar networks were plate-like and sieve-like. The pleural superficial blood vessels were smooth, while the round imprints of endothelial nuclei along the vascular axis and circular constrictions were found on the subpleural arteriole and the terminal arteriole. The round depressions occurred on the surface of the venule in the lung parenchyma.The pleural superficial and the subpleural vascular networks also occurred in the adult cattle lung. The subpleural arteriole and its branches were short. The subpleural capillary meshes were sparse and web-like, and small holes made of microvessels were found occasionally. The anastomosing occurred between the pleural superficial and the subpleural vascular networks on the capillary level or the precapillary level. The honeycomb vascular networks were also various in size and form at a low magnification. The venule connected with the pulmonary capillary networks directly at a high magnification. The single capillary networks were found in the alveolar septa. The longitudinal crests and dense round imprints of endothelial nuclei and the clear circular constrictions were found on the surface of the larger vessel in the lung parenchyma. The round imprints of endothelial nuclei also occurred on the subpleural venule and capillary.The analysis and comparison on the pulmonary microvasculature showed that there were many common characters among 180-day old yak, the adult yak and the adult cattle. The superficial microvascular networks were sparser, while the subpleural microvascular networks were denser. The superficial blood vessels and the interlobular blood vessels were mutual transitional, and the anastomosing between the superficial blood vessels with the subpleural vessels. According to the branching sequence of the subpleural arteriole, it could be divided into the arteriole, terminal arteriole, precapillary arteriole and capillary in turn. The subpleural capillary networks were mainly web-like, while small holes were also found on the cast. The honeycomb vascular networks were various in size and form at a low magnification. The outline of alveolus, alveolar sac, alveolar duct and respiratory bronchiole and terminal bronchiole, made of microvascular networks, could be found in the cut surface. The pleural superficial blood vessels were smooth, while the constrictions of smooth muscle cells and round imprints of endothelial nuclei occurred on the surface of the subpleural and parenchymal arteriole and venule. However, the pulmonary microvascular networks were sparser, and the vascular were larger in diameter with aging. The results from comparison of the pulmonary microvascular construction among 180-day old yak, the adult yak and one-day old yak showed that the plate-like vascular networks occurred in 180-day old yak lung, while the web-like alveolar capillary networks were found in the adult yak lung. Moreover, the significant differences on the pulmonary vascular networks were found between the adult yak and cattle lung. The pleural superficial, subpleural and parenchymal vacular networks were denser, and the range of the microvessels in diameter were larger, and the proceeding distance of the subpleural arteriole and its branches were longer in the adult yak lung than those in the adult cattle lung. However, the anastomosing between the pleural superficial and the subpleural vascular networks were more often found in the adult cattle lung than that in the adult yak.In conclusion, the pulmonary microvascular networks in the yak were much denser than that in the cattle, and the distributing range were much wider in the yak than the cattle. And the microvascular networks decreased gradually in density with aging in the yak. Therefore, the distribution of dense microvascular networks was one of the important characteristics in the yak lung, which could be one of the important adaptive structures of yak to the highland and hypoxia environments.