Maina J N
School of Anatomical Sciences, Faculty of Health Sciences, The University of the Witwatersrand, 7 York Road, Parktown, 2193 Johannesburg, South Africa.
Anat Embryol (Berl). 2003 Sep;207(2):119-34. doi: 10.1007/s00429-003-0333-6. Epub 2003 Jul 11.
The lung buds were first conspicuous on day 3 of embryogenesis. They fused on day 4 and the common growth divided into left and right primordial lungs on day 5. Progressively, the lungs elongated, diverged, and advanced towards the respective dorsolateral aspects of the body wall, reaching their definitive topographical locations in the coelomic cavity on day 6. On day 7, they rotated, attached onto the ribs, gradually started to slide into them, and were deeply inserted by day 8. The primary bronchus (PB) first appeared as a solid cord of epithelial cells (day 4) that successively canalized as it invaded the surrounding mesenchyme, extending along the proximal-distal axis of the lung. From day 8, the secondary bronchi (SB) begun to sprout from the PB in a craniocaudal sequence. On day 9, the parabronchi (PR) started to bud from the SB, projecting into the adjacent mesenchyme. They commenced to canalize on day 10 and greatly increased in length, number, and diameter. By day 13, the PR had anastomosed profusely and totally masked the SB. The luminal surface of the PR was lined by a columnar epithelium from which the atria (day 15), infundibulae (day 16), and air capillaries (ACs) (day 18) developed. At hatching (day 21), the ACs were well developed and had anastomosed profusely with the blood capillaries. Of the air sacs (ASs), the abdominal ones appeared earliest (day 5) followed by the cervical ones on day 6. In quick succession, the other ASs were well formed by day 10. After hatching, no further consequential structures formed: only shifts in topographical locations and an increase in size and number occurred. Morphogenetically, the avian respiratory system differs from the mammalian one in certain key aspects: besides the ASs that are unique to it, the lung is exceptionally complex in structure and is essentially mature at the end of the embryonic life.
肺芽在胚胎发育第3天首次显现。它们在第4天融合，共同生长在第5天分为左右原始肺。逐渐地，肺伸长、分开，并朝着体壁各自的背外侧延伸，在第6天到达体腔中其最终的位置。在第7天，它们旋转，附着于肋骨，逐渐开始滑入肋骨，并在第8天深深嵌入。初级支气管（PB）最初表现为上皮细胞的实性索（第4天），在侵入周围间充质时依次形成管腔，沿肺的近-远轴延伸。从第8天开始，次级支气管（SB）开始以头尾顺序从PB发出。在第9天，副支气管（PR）开始从SB发出，伸入相邻的间充质。它们在第10天开始形成管腔，长度、数量和直径大幅增加。到第13天，PR大量吻合，完全遮盖了SB。PR的管腔表面衬有柱状上皮，心房（第15天）、漏斗部（第16天）和空气毛细血管（ACs）（第18天）从这里发育而来。在孵化时（第21天），ACs发育良好，并与毛细血管大量吻合。气囊（ASs）中，腹部气囊最早出现（第5天），其次是颈部气囊在第6天出现。很快，其他ASs在第10天发育良好。孵化后，没有进一步形成重要结构：只是位置发生了变化，大小和数量有所增加。在形态发生上，鸟类呼吸系统在某些关键方面与哺乳动物不同：除了其特有的ASs外，肺的结构异常复杂，在胚胎期结束时基本成熟。
