Figure 21.

Resolution of the pulmonary venous myocardium. With light microscopy, a myocardial sleeve in intrapulmonary veins can appear similar to smooth muscle, unless smooth muscle-specific probes are utilized. Light (A, scale 25 μm) and electron (B, scale 2 μm) micrographs of a small pulmonary vein (lumen diameter ~ 100 μm) from the same block of rat lung highlight this point. For light microscopy, a 1 μm section of plastic embedded glutaraldehyde-fixed lung prepared for transmission electron microscopy was stained with toluidine blue. The media in this image is notable only by its relative thickness and density. A transmission electron micrograph of an 80 nm section from the same block elucidated the presence of a cardiac myocyte rather than smooth muscle in the media. PV, lumen of the pulmonary vein; Alv, alveolar space.