The pulmonary arteries of the yak.

A quantitative histological study was carried out on the pulmonary arteries of a female yak (Bos grunniens), a member of the genus Bos which comprises the various types of cattle. A characteristic feature of cattle is a muscular pulmonary vasculature which responds sensitively to alveolar hypoxia by constriction. The yak studied had thin-walled pulmonary arteries and showed no evidence of right ventricular hypertrophy. It is suggested that this may be a feature of adaptation (as contrasted to acclimatisation) to a life in the hypobaric hypoxia of high altitude.