The Vasculature Of Venules In The Pulmonary Parenchyma On Yak And Sheep Under Scanning Electron Microscope (SEM)

Lungs of yaks and sheep were cast by pulmonary venous perfusion and then prepared for observation in SEM. The results showed that the vasculature of venules in the pulmonary parenchyma on yak is similar with that on sheep. At low magnification, the outline of the comblike alveolar cavities, the alveolar sacs, the alveolar ducts, the respiratory bronchioles and the terminal bronchioles were described. The alveolar cavities were made of single-layer capillary networks and the alveolar cavities varied in size. The alveolar cavities were half-hollow spheres, concave to outside and base to inside. The meshes of the alveolar capillary networks varied in size and shape. The shapes of the meshes of the alveolar capillary networks were polygonal, circular, elliptical, and irregular, etc. The venules and their branches proceeded in the alveolar septa, or ran among the several alveoli. The postcapillary venule, the collecting venule and the venule could be described in the section. The branches of the venules were"dendritic". From the"treetop"to the"stem of tree", the structures were followed: the pulmonary alveolar capillary network, the postcapillary venule, the collecting venule and the venule. The main refluxing pattern of the venules was from the alveolar capillary network to the postapillary venule, to the collecting venule, till the venule. And the capillaries were also directly drained into the collecting venule or the venule. The circular constructions of the smooth muscle cells were found on the cast surface of the venules in yak and sheep, and the number of the constructions would decrease gradually as the diameter of the venules decreased. At the junction of the postcapillary venule and the alveolar capillary, the postcapillary venule constricted significantly in size. The circular imprints of the endothelial nuclei were also found on the cast surface of the alveolar capillaries. The distribution and the refluxing pattern of the venules in the pulmonary parenchyma on yak and sheep were described in the present study, and these contents provided the new data for the comparative anatomy.