Structural organization of pulmonary veins in the rat lung, with special emphasis on the musculature consisting of cardiac and smooth muscles

Abstract

Recent physiological studies have indicated the significant role of pulmonary veins in the total resistance of pulmonary vasculature. The structure of pulmonary veins in the rat was reinvestigated to clarify the different venous segments and their ultrastructure with regard to the musculature including cardiac muscles and smooth muscles with light and electron microscopy. The cardiac muscles were located in the axial and the primary branches of the pulmonary veins within a certain distance limit from the hilum (CM segment) and not in the peripheral region (non-CM segment). The smooth muscles were found indifferent to the presence of cardiac muscles as a continuous layer in segments larger than 180 microm (continuous SM segment) or as a discontinuous layer of circular smooth muscle cells in segments between 50 and 180 microm (partial SM segment). The smooth muscle layer was extremely thin in the CM segments, whereas it became conspicuously thick in the non-CM segment with an irregularly undulating luminal outline, especially in the partial SM segments. There were two elastic laminae in the CM segments: a conspicuous one on the interstitial side of the smooth muscles, and a weaker one between the endothelium and smooth muscles. In the non-CM segment, one elastic lamina was found on the interstitial side of the smooth muscles. Considering the limited range of contraction of cardiac muscles and the thinness of smooth muscle cells in the CM segments, it was concluded that vasoconstriction in the pulmonary veins is executed by smooth muscle cells in the non-CM segments thicker than 50 microm.

Structural Organization of Hepatic Portal Vein in Rat with Special Reference to Musculature, Intimal Folds, and Endothelial Cell Alignment

“…Some veins near left or right atrium contain cardiac muscle outside of CSM (Cullinan et al,1986; Endo et al,1994; Endo et al,1997; Hashizume et al,1998; Hosoyamada et al,2010). Yokota and Yamauchi (1985) clearly showed cardiac muscle in the wall of mouse HPV by light and transmission electron microscopy.…”

“…Unlike arteries, some veins possess longitudinal smooth muscle (LSM) in their wall inside or/and outside of the layer of CSM (Ferraz‐de‐Carvalho et al,1994; Wali et al,2003). Moreover, veins near left or right atrium contain cardiac muscle outside of CSM in a variety of mammals (Cullinan et al,1986; Endo et al,1994; Endo et al,1997; Hashizume et al,1998; Hosoyamada et al,2010). The structural diversity of venous wall is likely to result from an influence of surrounding environment including external forces (Bloch and McCuskey,1973), what factors are involved in the determination of structural organization in each vein is not yet fully understood.…”

Lung, Pleura, and Mediastinum

“…The pulmonary venous system drains the pleura, alveoli, bronchioles, and most bronchi. The confluence of veins from the pulmonary lobules form pulmonary veins, one from each lobe, that join to form a single pulmonary vein drain into the left auricle (Nakakuki, 1983;Hosoyamada et al, 2010). The bronchial veins drain the trachea, esophagus, lungs, bronchi, and associated lymph nodes and enter the superior vena cava.…”

“…The cardiac muscle is present in the axial vein and its primary branches closer to the hilum. As the pulmonary vein branch and go deeper, they lose cardiac muscle layer (Almeida et al, 1975;Hosoyamada et al, 2010). Disease processes that affect cardiac muscle can affect that of the pulmonary veins as well.…”

Organ Specificity and Functional Relevance of the Arterial Structure: A Comparative Study in the Kidney and the Skeletal Muscle with Electron Microscopy

“…The structure of these minute vessels has been well visualized and studied with advanced microscopic techniques, including transmission and scanning electron microscopy and confocal microscopy. These studies elucidated the common basic structure of the arterial and venous wall, including the endothelium, the inner elastic lamina, smooth muscle cells in the media and adventitial connective tissue [1,2,3,4,5,6], as well as the different configuration of endothelial cells in the arteries [7] and in the capillaries [8]. …”