| Objects：Yak as a unique native species of the living in Qinghai-Tibet plateau, the pulmonarycirculation has fully adapted to the plateau low oxygen environment. In order to accuratelydetermine the nature and positioning of lung pulmonary artery branch segments of the yak,so pulmonary artery of the yak was systematic studied by means of gross anatomy, X-rayimaging, optical microscope and transmission microscope technology. At the same time,by comparison with tissue structure of plain cattle pulmonary artery, for the sake ofproviding a morphology basis for the adaptability of pulmonary artery of yak to plateaulow oxygen.Methods：1. Acquainting the whole lung specimens and different diameter pulmonary arterytissue samples of newborn yak,5months yak, adult yak and plain cattle, observing the yakpulmonary artery branch distribution and measuring initial diameter size through posturesmicroscope micro-dissection, barium sulfate perfusion and X-ray transmission. Makinglens tissue section and using the dyeing methods of H-E staining, Verhoeffe ’s Van gessionstaining and Massion three color to observe structure of yak pulmonary artery branches atall levels and all ages of newborn yak,5months yak, adult yak and adult cattle pulmonaryartery. Making ultra-thin tissue section and observing superfine organization structurechange of the yak pulmonary artery wall in all ages and all levels.2. Through the Image-Pro express software to measuring and calculating MT quantityof all ages and yaks and adult cattle pulmonary membrane, statistic and analysis throughthe EXCEL2010software.Results：1. The right pulmonary artery branch is better than left pulmonary artery branch ofyak, there are16-17pulmonary artery segment of left pulmonary artery branch of grade1 to3, correspond forming16-17pulmonary arterial branch, there are20-22pulmonaryartery segment of right pulmonary artery branch of grade1to3, correspond forming20-22pulmonary arterial branch.2. The yak’s pulmonary artery is divided into five types according to its tissuestructure characteristics; it is respectively classical elastic pulmonary artery (CE),transitional elastic pulmonary artery (TE), transitional muscular pulmonary artery (TM),classical muscular pulmonary artery (CM), pulmonary muscular arteriole (PMA). Thediameter of pulmonary artery above2000μm was defined as a classical elastic pulmonaryartery in the newborn yak, belonging to the first and second level pulmonary artery branchsegments. The diameter of pulmonary artery between1000μm to2000μm was defined astransitional elastic pulmonary artery, belonging to the third and fourth level pulmonaryartery branch segments. The lobus cardiacus, ventral side of lobus diaphragmaticus, andlobus apicalis belong to the fourth level pulmonary artery branch segment. The dorsalsection was a third level branch section. The diameter of pulmonary artery below1000μmwas defined as muscular pulmonary artery.3. In the tunica media of elastic pulmonary artery segment, the CE intrapulmonaryartery comprises a large number of elastic membrane and smooth muscle cells scatteredamong elastic membranes. Near the lumen surface, elastic membranes are denselydistributed, and elastic fibers gradually became sparse on to the outer membrane along thepulmonary artery wall near the outer membrane. In the clearly artery outer membrane ofhilus of pulmonary artery, there are massive smooth muscle, elastic membranes are unevendistributed, near the lumen surface, the elastic membrane gradually became parallelarrangement, there are small amount collagen fibers on both sides of elastic membrane.The TE intrapulmonary artery exhibit two main forms, one type is the CE artery extension,whereby the smooth muscle cells are still irregularly arranged in the tunica media.However, the number of smooth muscles increased significantly. In the adventitia of thisTE artery, smooth muscles are found bundled in parallel with the long axis of thepulmonary artery. These smooth muscles were wrapped in rich elastic fiber and collagenfiber in the adventitia membrane-rich collagen fibers. This type of TE pulmonary artery is often observed in adult yak intrapulmonary artery and is rarely observed in newborn yaksand5month yaks. Between the elastic membrane, there are three conjunctive forms, oneis small branch from both sides and another small branch from the top of the dominantelastic fibers and linked smooth muscles, the third form is that the TE arterial wallexhibited smooth muscle hiatus phenomenon, where in the absence of smooth muscleareas, both sides of smooth muscles are linked by collagen and elastin fibers. Smoothmuscle distribution is the differentiating characteristic of the second type of TE artery. Thesecond type transition section structure characteristic of pulmonary artery is that thecircular arrays of smooth muscles and elastic membrane exist along the pulmonary artery.Near the lumen surface, elastic membranes are arranged closely together, but near theadventitia, elastic membranes are loosely arranged.By TEM observation of the tunica media of the CE intrapulmonary artery, smoothmuscle cells are flat, and have more protuberances with various lengths. Smooth musclecells are interconnected by the protuberances and connected with the collagen fibers andelastic membranes (or elastic fibers). In the smooth muscle cells, few glycogen granulesand mitochondria were found. In the TE intrapulmonary artery, collagen fiber contentincreased in the surrounding smooth muscle cells, and collagen fibers were massivelydistributed. Numerous protuberances were found in the surface of the smooth muscle cells,which contained more mitochondria, and microfilaments were likewise observed.However, in the CE pulmonary artery, the microfilament was not found in smooth musclesof the tunica media. Furthermore, the smooth muscle of TE intrapulmonary artery tunicamedia contained more glycogen granules.4. In the muscular pulmonary artery segment, two transitional forms exist betweenthe TE pulmonary artery and the TM pulmonary artery. One mechanism postulates thatelastic membranes and fibers increased gradually in the transitional position. The numberof smooth muscles dramatically decreased, almost completely replaced by elasticmembranes and elastic fibers that converged a few layers parallel to the elastic membranes,which subsequently entered the TM intrapulmonary artery and gradually changed into twoto three layers. Another phenomenon was that the elastic membrane gradually changed into a bunch, and then produced one to two layers of elastic membrane before going intothe TM artery. In the TM artery, a great number of plicas were observed due to the elasticmembrane promontory. The integrated internal and outer elastic membrane was still found,but it was not continuous in tunica media of TM artery, where the elastic fiber sizes wereuneven. The main features of CM segment have three to eight layers smooth muscle, theinternal elastic membrane structure integrity was preserved in the media but the originalexternal elastic membrane was not retained. The outer membrane was consisted of a fewelastic and collagen fibers. Integrated smooth muscle cells about one to two layers werestill found in tunica media of the intrapulmonary arteriole under50-μm diameter PMA.Elastic fibers disappeared between smooth muscle cells, but internal elastic membranewas still intact.At the point where the TM intrapulmonary artery begins, because of elasticmembrane discontinuity through the smooth muscle, elastic membrane and collagen fibersare interwoven between smooth muscle, collagen fibers can be found in regions withoutelastic membrane. The smooth muscle cells rely on many filamentous apophysis, morecollagen fibers were found between smooth muscle cells, and there were glycogenosomewithin the cells. In a CM intrapulmonary artery, smooth muscle parallel distribution, thecell surface has more apophysis, and more glycogenosomes can be found within smoothmuscle.Conclusion:1. In the pulmonary artery of yak, right pulmonary artery segment relative to the leftlung pulmonary segment developed, especially, the difference is more obvious betweenthe pulmonary artery segment of lobus apicalis and lobus cardiacus, beginning from thegrade4thbranches, the diameter of pulmonary artery segment of lobus apicalis, lobuscardiacus, accessory lobe and ventral diaphragmatic lobus is below1mm, turning intomuscular artery. But in the dorsal diaphragmatic lobus, beginning from the grade3thbranches, the diameter of every pulmonary artery segment is below1mm, turning intomuscular artery (Including transitional muscular pulmonary artery and classical muscularpulmonary artery). 2. The yak’s pulmonary artery is divided into five types according to its tissuestructure characteristics; it is respectively classical elastic pulmonary artery (CE),transitional elastic pulmonary artery (TE), transitional muscular pulmonary artery (TM),classical muscular pulmonary artery (CM), pulmonary muscular arteriole (PMA).3. In the transitional elastic pulmonary segments, there are three kinds of connectionsbetween elastic fibers and smooth muscle, mainly for the top connections of the elasticfibers, elastic fibers on both sides of the branch to connecting, and directly join smoothmuscle on both ends of the elastic fibers. In the process of transformation of elastic totransitional muscular artery, there are two main forms of changes, a kind of transitionalelastic artery is that elastic fibers increased gradually at close to the transition of elasticmembrane, and smooth muscle significantly reduce in the transition place, it is replacedby elastic membrane and elastic fiber, then joining into a few layer parallel elasticmembrane, turning into the transitional muscular artery and gradually become severallayers elastic membrane. Another transitional form is that transitional elastic artery elasticmembrane gradually gathered into a bundle of elastic membrane, and then forming1to2layer elastic membrane, turning into the transitional muscular pulmonary artery.4. The adult plain cattle smooth muscle of pulmonary artery wall loss under100μmdiameter, but the external elastic membrane is integrity, when the diameter of the yakpulmonary micro artery is under50μm, it can be still observed the integrated smoothmuscle layer and internal elastic membrane. The MT value differences of adult yaks andadult cattle mainly reflects on the pulmonary artery under200μm, when the diameter isgreater than200μm, the MT value changing of adult yaks and adult cattle is the same,namely, in the pulmonary artery portal, the MT are basically the same, Illustrating theinfluence of hypoxia on pulmonary artery structure mainly reflects on the pulmonaryarterioles, the larger MT value of pulmonary arteriole of adult yak may be its adaption tohypoxic condition of structure foundation. |
