Observation The Histological Structure And Distrbution Of Bronchial Arteries Of The In Different Age Yak(Bos Grunniens)

Histological and morphometric methods were used to study the histological and morphological structure of yak's bronchial arteries in different ages. The results showed that almost directly after emerging from the aorta, the branch of yak's bronchial arteries was distributed from bronchus to respiratory bronchioles and pleura , interlobular septum, lymph nodes, pulmonary arteries and veins, the perineurium of vagus and near the tracheal gland .The media of the bronchial arteries bcome principally muscular. There is a little longitudinal muscular fibers in the intima of bronchial arteries from aorta. But when they have penetrated the bronchial wall, a subendothelial layer of longitudinal muscular fibers appears in the intima. The elastic interna in between splits, and forms fibrillae which surround the longitudinal muscular fibers. Near the tunica intima , bundles of longitudinal smooth muscle were observed and increased with the process of age, even it could expand to media and made the media thin, then the intima was thicken . The percentage of medial muscle thickness of pulmonary artery (MT%) variation was different, and the mean of MT% was 28.01±10.65%(newborn),29.81±11.17%(juvenile),34.05±10.87%(one-year-old)and 33.30±11.03%(adult), respectively , and the thickness of media was thickest in one-year-old group.?Compared in the same age, the MT% of bronchial arterioles whose diameter was less than 50μm were largest. In the groups that the diameter of bronchial arterioles was 14.88±3.87μm ( newborn ),17.18±3.10μm(juvenile),17.70±3.23μm(one-year-old)and17.54±1.87μm(adult),we observed that there were smooth muscle ,and even discontinuous internal elastic membrane in arterioles. With the growth of yak, it suggested that the hypoxia could also influence significantly the bronchial arteries of the yak, especially whose diameter was less than 50μm.? The? author thought the structural rebuilding of bronchial arteries which lead to media thicken, and the increase of smooth muscle was a structure adaptation to the hypoxia.