Fine structure of the mouse portal vein in relation to its peristaltic movement

The hepatic portal vein has been known to make a spontaneous peristaltic movement in some mammals, including the mouse and rat. To investigate the fine structure of the portal vein in relation to its physiological characteristics, we observed the mouse portal vein by using various histological techniques including conventional light microscopy, videomicroscopy, transmission and scanning electron microscopy, and real-time confocal laser scanning microscopy. The mouse hepatic portal vein was provided with a spiral fold which was produced by the inner layer, i.e. the endothelium and smooth muscles of the wall protruding into the lumen. Longitudinal smooth muscle cells spanned the interval of the fold, like a spirally arranged palisade around the vessel wall. The longitudinal muscle fibers ended at the spiral fold, being partly connected with a network of irregularly shaped smooth muscle cells. This network, hitherto unknown, was recognized to be restricted to the fold in distribution and characterized by numerous gap junctions connecting the muscle cells. Real-time confocal laser scanning microscopy using a Ca2+ sensitive fluorescent dye revealed that a transient and periodic increase in Ca2+ concentration occurred in the longitudinal smooth muscle cells and was transmitted spirally from the intestinal to the hepatic side. These findings indicate that, during the peristaltic movement, the contraction of smooth muscle cells is transmitted along the longitudinal smooth muscles of the portal vein wall toward the liver, presumably controlled by the network of the irregularly-shaped smooth muscle cells in the fold of the portal vein. Light microscopic observation in some specimens indicated an occurrence of cardiac muscle cells outside the smooth muscle layer. Restricted to the site of the porta hepatis in distribution, their involvement in the peristaltic contraction of the portal vein seemed unlikely.     

Scanning electron microscopy of an elastic fiber network which forms the internal elastic lamina in canine saphenous vein

Scanning electron microscopy (SEM) was used to study the arrangement of elastic fibers in the canine saphenous vein as the basis for further studies of veins used in by-pass grafting operations. The elastic fiber arrangement in distended and non-distended veins was examined in both immersion-fixed and perfusion-fixed vessels. Transmission electron microscope (TEM) observation of the SEM samples confirmed the identity of these fibrillar structures as elastic fibers. In addition, specific stains for elastic fibers (Verhoeff's iron hematoxylin and orcein) were used. The elastic fibers forming the internal elastic lamina were arranged in a fishnet-like pattern. Large-diameter fibers, running longitudinally along the vascular wall, were interconnected by smaller oblique fibers. Together the fibers formed an elastic cylindrical network between the endothelium and the smooth muscle cells. The thicker longitudinal fibers were the same diameter in distended and non-distended veins. By contrast, the oblique fibers were thinner and more complexly branched in distended veins. The architecture of the elastic fiber network contributes to vascular flexibility and allows circumferential distension. The interconnecting oblique fibers presumably serve to distribute internal pressure equally around the venous wall.     

Scanning and transmission electron microscopy of venous sphincters in the rat lung

The rat pulmonary microvasculature was studied using scanning and transmission electron microscopy of vascular corrosion casts and tissue sections. Special emphasis was placed on small pulmonary venous vessels. The shape of vascular casts was analyzed and interpreted concerning the wall composition of corresponding vessels studied in tissue sections. On the casts of pulmonary venules and small pulmonary veins, narrow or wider annular constrictions were regularly observed. Within these constrictions, marks of circularly running grooves were seen as an additional structural detail, which obviously mimic impressions of single or grouped smooth muscle cells. The depth of the constrictions varies; it may be more or less pronounced, occasionally narrowing down the luminal diameter to approximately 50%. These constrictions are caused by muscular sphincters. In tissue sections of small pulmonary veins, sphincter regions were identified as abruptly appearing single or grouped true smooth muscle cells. Smooth muscle cells may be arranged side by side in a group or bundle or even staked in two or three layers. Between the sphincter regions, the venous wall consists merely of endothelium and an accompanying connective tissue layer. The smooth muscle cells of a sphincter are regularly positioned between endothelial layer and elastic lamina. The smooth muscle cells next to the endothelium form myoendothelial junctions. Autonomic nerves near the sphincters were never seen. The venous sphincters described are suggested to be effective devices involved in blood flow regulation. Blood-borne substances or local tissue hormones might govern sphincter function. © 1992 Wiley-Liss, Inc.     

Scanning and transmission electron microscopy of venous sphincters in the rat lung.

The rat pulmonary microvasculature was studied using scanning and transmission electron microscopy of vascular corrosion casts and tissue sections. Special emphasis was placed on small pulmonary venous vessels. The shape of vascular casts was analyzed and interpreted concerning the wall composition of corresponding vessels studied in tissue sections. On the casts of pulmonary venules and small pulmonary veins, narrow or wider annular constrictions were regularly observed. Within these constrictions, marks of circularly running grooves were seen as an additional structural detail, which obviously mimic impressions of single or grouped smooth muscle cells. The depth of the constrictions varies; it may be more or less pronounced, occasionally narrowing down the luminal diameter to approximately 50%. These constrictions are caused by muscular sphincters. In tissue sections of small pulmonary veins, sphincter regions were identified as abruptly appearing single or grouped true smooth muscle cells. Smooth muscle cells may be arranged side by side in a group or bundle or even staked in two or three layers. Between the sphincter regions, the venous wall consists merely of endothelium and an accompanying connective tissue layer. The smooth muscle cells of a sphincter are regularly positioned between endothelial layer and elastic lamina. The smooth muscle cells next to the endothelium form myoendothelial junctions. Autonomic nerves near the sphincters were never seen. The venous sphincters described are suggested to be effective devices involved in blood flow regulation. Blood-borne substances or local tissue hormones might govern sphincter function.     

Ultrastructural changes of smooth muscles in varicocele veins

Background: Varicocele is a dilatation of the pampiniform venous plexus and internal spermatic veins. It affects about 15-20% of male population and can cause infertility. Objective: To describe the most significant ultrastructural changes of the smooth muscle cells in grade 3 varicocele veins. Methods: The authors analyzed 2- to 3-cm tracts of pampiniform venous plexus from 20 patients who underwent varicocelectomy for left varicocele. Light microscopic examination was performed with Van Gieson's stain. Ultrastructural examination was done using scanning and transmission electron microscopy. Results: Light microscopic examination revealed irregularity and separation of medial smooth muscle cells by abundant collagen fibers in varicocele veins. On scanning electron microscopy, the medial layer of varicocele veins showed hypertrophy, irregularity, and separation of the outer longitudinal smooth muscle cells and deposition of numerous fatty globules in between muscle fibers. Transmission electron microscopy showed marked indentation and chromatin condensation of the nucleus, presence of clear vacuoles and myelin figures in the cytoplasm and plasmalemmal projections and formation of ghost bodies. Furthermore, smooth muscle cells were found to have pseudopodia-like projections around adjacent elastic and collagen fibers. Conclusions: The degenerative changes observed in smooth muscle cells and presence of abundant collagen fibers in the medial layer may contribute to the development of the varicocele of pampiniform venous plexus. Further molecular studies are required to shed more light for the underlying mechanism.     

Electron microscopic research on the venous valves of the lower extremities in varicose veins

Electron microscopy of the venous valves in varicose disease shows that dystrophic changes develop on the external and internal surfaces of the valve cusps. Endotheliocytes on the external surface are located longitudinally in relation to valvular axis and on the internal surface they are perpendicular to it. Fragments of the elastic membrane, collagen fibres and smooth muscle cells are seen under the endothelial lining. Endothelium actively regulates proliferative processes of smooth cells secreting the so-called "growth factor of endothelial origin". The development of venous valve pathological changes in varicose disease is accompanied by endothelial damage, disturbance of morphofunctional state of smooth muscle cells and intercellular substance of the vascular wall.     

Architecture of the caudal vena cava wall of the dog at the level of the liver caudate lobe

The vascular segment of the caudal vena cava of the dog at the level of the caudate lobe was shown to be intimately related to hepatic tissue through the hepatic capsule and parenchyma. The tunica adventitia of the caudal vena cava was formed mainly by smooth muscle cells with collagen and elastic fibers arranged in bundles. The thin tunica media of the vein was also formed by smooth muscle cells, collagen and elastic fibers arranged in bundles. The tunica intima presented an elastic subendothelial network. The hepatic segment of the caudal vena cava showed a myoconnective architecture and propulsive characteristics in terms of its hemodynamic pattern.     

Ultrastructural Changes of Smooth Muscles in Varicocele Veins

Background: Varicocele is a dilatation of the pampiniform venous plexus and internal spermatic veins. It affects about 15–20% of male population and can cause infertility.

Objective: To describe the most significant ultrastructural changes of the smooth muscle cells in grade 3 varicocele veins.

Methods: The authors analyzed 2- to 3-cm tracts of pampiniform venous plexus from 20 patients who underwent varicocelectomy for left varicocele. Light microscopic examination was performed with Van Gieson’s stain. Ultrastructural examination was done using scanning and transmission electron microscopy.

Results: Light microscopic examination revealed irregularity and separation of medial smooth muscle cells by abundant collagen fibers in varicocele veins. On scanning electron microscopy, the medial layer of varicocele veins showed hypertrophy, irregularity, and separation of the outer longitudinal smooth muscle cells and deposition of numerous fatty globules in between muscle fibers. Transmission electron microscopy showed marked indentation and chromatin condensation of the nucleus, presence of clear vacuoles and myelin figures in the cytoplasm and plasmalemmal projections and formation of ghost bodies. Furthermore, smooth muscle cells were found to have pseudopodia-like projections around adjacent elastic and collagen fibers.

Conclusions: The degenerative changes observed in smooth muscle cells and presence of abundant collagen fibers in the medial layer may contribute to the development of the varicocele of pampiniform venous plexus. Further molecular studies are required to shed more light for the underlying mechanism.     

Structural identification and characterization of arteries and veins in the placental stem villi

The vascular wall structure in the human full-term placental villi of normal pregnancy was studied by means of light and electron microscopy with an improved technique of perfusion fixation and tissue preparation. We observed 81 sections of stem villi that showed cross-sectional profiles of paired vessels in their center. Both vascular walls contained a large amount of extracellular matrix and no elastic lamina between smooth muscle cells of the media, making identification of the artery and the vein quite difficult at first sight. We then noted that the density of the smooth muscle cell population was always considerably higher in one than the other, and identified the former as artery and the latter as vein on the basis of their connection with larger arteries and veins running on the chorionic plate. Between the paired vessels, the artery had a smaller caliber than the vein, and the ratio of venous to arterial caliber was distributed from 1.0 to 2.5. The thickness of media was usually thicker in the vein than in the artery. Clusters of elastic fibers were found occasionally in the media of arteries and veins, and basement membrane-like materials were associated frequently with the elastic fibers and were distributed widely in the media as well as in the adventitia. In the veins, the smooth muscle cells of the most superficial part of the media contained well-developed rough endoplasmic reticulum and Golgi apparatus, indicating differentiation to secrete extracellular matrices. The present study revealed the difference of wall structure between arteries and veins in the placental stem villi for the first time at the ultrastructural level, and suggested differentiation of venous smooth muscle cells, possibly by some influence from the luminal side.     

Scanning electron microscopy of aortic medial changes in aortic ascending dilatation

The study of cystic cavities and collagen fibers fragmentation is useful to for a better knowledge of pathogenesis and surgical therapy of medial ascending aortic degeneration. Thus, the aim of this study was to describe by scanning electron microscopy the surfaces and shape of the cysts, measure their area, and identify microcystic spaces related to this degenerative disease. Scanning electron microscopy analysis was performed in 16 out of 36 patients who underwent surgery for ascending aorta dilatation with associated aortic valve disease. The aortic medial wall showed a cribrose appearance at low magnification (×50-100) and the intima was effuse. At high magnification (×500-2000), small cavities (clefts) lined by normal or fragmented elastic fibers and large cavities (pseudocystes) with anfractuous borders lined by fragmented elastic fibers and smooth muscle cells were observed. Furthermore, in the outer media wall microvessels lined by endothelium were also observed. These changes were lacking or less pronounced in normal aorta. SEM allows one to better identify the pathological cavities and to differentiate them from microvessels. These pathological cavities are more numerous and larger in the convexity than in the concavity of the aorta in according to our previous morphological and morphometric findings in asymmetrical aorta dilatation.