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)

摘要： 本实验选取40 份不同胎龄的牦牛肺脏样本,通过组织学和组织化学的方法对牦牛肺发育过程进行研究,旨在为发育生物学提供形态学资料。结果表明,牦牛胚胎肺发育可分为5 个时期:(1)胚胎期(30 ～ 50 d),胚胎出现肺芽,其分支形成主支气管,进一步分出叶支气管,上皮均为假复层柱状上皮; (2) 假腺期(50 ～120 d),支气管树发育明显,末端终蕾结构似腺体,为假复层柱状上皮;(3)小管期(120 ～180 d),呼吸部发育明显,终蕾腺泡样结构消失,可见多处管状分支,上皮为单层柱状或单层立方; (4)囊状期(180 ～220 d),终囊管壁由较厚肺泡隔及原始肺泡组成,少数原始肺泡上皮分化为扁平的肺泡Ⅰ型细胞和立方形的肺泡Ⅱ型细胞;(5)肺泡期(220 ～ 260 d),形成肺泡,大部分上皮细胞分化为扁平的肺泡Ⅰ型细胞和立方形的肺泡Ⅱ型细胞。胚胎期和假腺期支气管和终蕾上皮的糖原含量丰富,从小管期开始,上皮细胞糖原含量开始急剧减少。之后的几个时期,只有导气部个别上皮细胞PAS 反应呈阳性。实验结果表明:牦牛胎儿的肺脏发育的特点与普通牛的基本相似,主要不同点是牦牛的囊状期较短,肺泡期较长,即牦牛胎儿的肺脏更早发育成熟。

关键词: 牦牛, 胎儿, 肺, 组织学, 发育