subpleural pulmonary microvasculature in newborn yak (Bos grunniens)

Yak is a unique domestic animal of Qinghai-Tibetan Plateau. Its unique adaptability to the high altitude environment has been hypothesized due to special pulmonary microvasculature. However, the anatomical evidence is still less. The present study characterized the subpleural pulmonary microvascular architecture of newborn yak by vascular corrosion cast and the scanning electron microscopy. The results showed the dense vascular network occurred in subpleural area in newborn yak. Subpleural vascular network was found in most of observed areas, while the sparse vascular network crept onto the subpleural network in some fields of view. The subpleural microvessels and their branches made up of the subpleural microvascular network. According to the branching sequence of vessels, the subpleural arterioles could be divided into four grades: the arteriole, terminal arteriole, precapillary arteriole and capillary. The subpleural capillary network in the local area could be classified into three different forms, including sheetlike vascular network, wrinkled vascular network and weblike vascular network. It was the specific characteristics on the cast surface of the microvessels that was the adaptable peculiarities. Anastomoses were found between the pleural microvessels and the interlobular capillaries, or between the pleural microvessels and the subpleural capillaries, or between the interlobular capillaries and the subpleural capillaries. Therefore, there was significant difference on the subpleural pulmonary microvasculature between newborn yak and other adult mammals.