关键词: 牦牛, 胎儿, 肺, 组织学, 发育

Abstract: Lung tissue from 40 yak fetuses of different age groups were collected to investigate their development process using histological and histochemical methods. The aim is to provide morphological data on developmental biology and find the hypoxia adaptive structure of the lung in yak fetus.The results showed that the developmental period of yak lung can be divided into five stages. (1)Embryologic stage (30 -50 days):a lung bud was found. Its branches formed into the primary bronchi,and then into the lobar bronchus.The bud had the pseudostratified columnar epithelium. (2)Pseudoglandular stage (50 - 120 days):the bronchial tree clearly developed and its terminal bud shaped like the gland.The bud possessed the pseudostratified columnar epithelium. (3)Canalicular stage (120 - 180 days):the respiratory region has rapidly grown,no glandular structure is found in terminal buds. There were many tubular branches with the single-walled columnar epithelium or cuboid epithelium. (4) Saccular stage (180 - 220 days):terminal sac (original alveolar)was formed by the ridge of dissepiment,and a few primitive alveoli epithelia differentiated into flat type I alveolar cells and cubical type Ⅱ alveolar cells.(5) Alveolar stage (220 - 260 days):the alveolus was formed. Much of the epithelium differentiated into flat type I alveolar cells and cubical type Ⅱ alveolar cells. We concluded from the present study that the epithelium of bronchial and terminal buds were full of glycogen in the Embryologic stage and the Pseudoglandular stage,and beginning from the Canalicular stage,the glycogen declined sharply. Several epithelium cells in the air conductivity portion were positive for PAS in the later stages.The developmental process of lung in yak fetuses is similar to that in cattle,although the yak has a longer saccular stage and a shorter alveolar stage The results suggest that the lung of yak fetus matures even earlier than that of cattle.

Key words: Development, Histology, Lung, Yak fetus(Bos grunniens)