The Microvasculature of the Larynx: A Scanning Electron Microscopic Study

In ten adult guinea pigs, the microvascular architecture of the larynx was evaluated using microvascular corrosion casts and scanning electron microscopy. The vocal cords were provided with a subepithelial capillary network. The capillaries, freely anastomosing with each other, were supplied and drained via strongly undulating arteries and veins. The undulation of the latter vessels may explain their adaptability to volume changes of the larynx during phonation. The vasculature of the internal perichondrium of the thyroid cartilage was interrupted at the anterior commissure where an avascular zone was present at the origin of the vocal cords. This avascular area is common to both guinea pigs and humans and may explain the particular mode of tumor spreading, i.e., that the tumors remain unilateral for a long time. The rich vascular supply of the laryngeal mucosa prevents the organ from ischemic complications during surgical procedures. Our results show that the guinea pig may serve as a model for study of laryngeal disorders

Luminal Constrictions on Corrosion Casts of Capillaries and Postcapillary Venules in Rat Exocrine Pancreas Correspond to Pericyte Processes

The rat exocrine pancreas was studied as a model to demonstrate morphological features of different types of capillaries, using scanning electron microscopy of vascular corrosion casts and transmission electron microscopy of tissue sections. Two types of capillaries were discerned. The first type represents less undulated, slender, straight capillaries with numerous, shallow, circular or semilunar furrows on its cast\u27s surface. In tissue sections, this type probably corresponds to non-fenestrated capillaries. The numerous grooves on its cast correspond to pericyte processes beneath the endothelial lining. The second type comprises capillaries of an undulated course and variable diameter with less numerous furrows. In addition, these casts showed circumscribed, smooth surfaced bulging areas defined by the grooves described. In tissue sections, this type probably corresponds to fenestrated capillaries, the bulging areas on its cast correspond to fenestrated regions of the endothelium. Fenestrated areas of capillary endothelium are less reinforced; pericyte processes are not present beneath these regions in tissue sections. The hypothesis that pericyte processes are responsible for surface indentations on capillary casts was supported by observations on postcapillary venules. Casts of these vascular segments showed also numerous circularly running furrows. Accordingly, the wall of postcapillary venules is provided with pericytes while smooth muscle cells are missing

Appearance of Venous Sphincters in the Pulmonary Microvascular Bed of Normotensive and Spontaneously Hypertensive Rats

The appearance of pulmonary venous sphincters was studied in normotensive and spontaneously hypertensive rats using scanning electron microscopy of microvascular corrosion casts and transmission electron microscopy of tissue sections. Vascular casts were prepared either after lavage with Tyrode solution or after glutaraldehyde prefixation. Pronounced pulmonary venous sphincters were more frequently identified in spontaneously hypertensive rats as compared to corresponding circular indentations in normotensive rats. Tissue sections established venous sphincters in hypertensive animals as consisting of multiple layers of smooth muscle cells in the venous walls. We did not observe any autonomic nerve terminals in close proximity to these bundles of smooth muscle cells. The effect of various casting procedures on the appearance of venous sphincters is discussed. It is concluded that glutaraldehyde prefixation is an appropriate method to demonstrate sphincter functioning, because it causes deepening of sphincter indentations. Pulmonary vascular sphincters are thought to be governed by blood-born substances, vasoactive metabolites, or by tension of oxygen and carbon dioxide. Venous sphincters may influence microvascular flow in general and probably substitute for venous valves in the pulmonary vascular bed where valves are missing

Casting with Mercox-Methylmethacrylic Acid Mixtures Causes Plastic Sheets on Elastic Arteries. A Scanning and Transmission Electron Microscopic Study

Lungs and systemic vessels of rats were cast with Mercox, both undiluted and diluted with monomeric methylmethycrylate (MMA; v:v/4:1), and studied by scanning electron microscopy (SEM). A sheet, less than 5 μm thick, surrounded the surface of cast pulmonary arteries and the aorta, when using diluted Mercox. This envelope was absent when casts were prepared with undiluted Mercox. Transmission electron microscopy (TEM) of unmacerated cast arteries showed all constituents of the vascular wall. Sections of thoroughly macerated vascular casts, however, still showed elastic lamellae in the vascular wall region, whereas muscular components and endothelial lining were completely digested. It is suggested that dilution of Mercox with MMA leads to phase separation during polymerization. An unidentified compound is released which penetrates the vascular wall, and makes preferentially the elastic lamellae resistant against tissue digestion. This assumption is supported by occurrence of such covering sheaths exclusively around elastic arteries

Different Forms of Corrosion Casts

We have previously described artifacts in corrosion casts prepared with Mercox®, diluted with methylmethacrylic acid (MMA). Using scanning electron microscopy (SEM) of casts and light microscopy (LM) of tissue sections, we found new forms of artifacts in casts prepared with both undiluted and MMA-diluted Mercox®. When undiluted Mercox® was used, most of the casts did not show artifacts. Artifacts were rarely seen and comprised empty casts consisting of a rim, while endothelial cell nuclear imprints and other vascular wall structures were replicated. Other casts sometimes showed vessels with a fine granular surface or some with conglomerates in their internal structure, however, surrounding vessels were well cast. When using MMA-diluted Mercox®, beside casts consisting only of a rim of resin, casts with granular surface, or casts composed of conglomerates, we found casts which were partially collapsed, casts with artifacts on many vessels, casts which only rudimentarily mimicked vascular structures, and finally casts which did not reveal any vascular structures. Light microscopy confirmed these findings and showed that the number of artifacts increases toward the periphery of an individual microvascular bed, demonstrated in intestinal villi as a model. The number of artifacts was higher when MMA-diluted Mercox® was used, regardless of the tissue or species used. Casts which did not replicate vascular structures were never found when undiluted Mercox® was used. Therefore, we recommend the use of undiluted Mercox® for the preparation of vascular corrosion casts

The Vascularization of the Digestive Tract Studied by Scanning Electron Microscopy with Special Emphasis on the Teeth, Esophagus, Stomach, Small and Large Intestine, Pancreas, and Liver

The periodontal vessels in adult rats show a ladder-like pattern; in guinea pigs molars, by contrast, they present a honey-comb pattern. The vascular architecture in human teeth seems to be similar to that of rabbits. In guinea pigs, rats, rabbits and humans esophagus circumferential vessels give off perforating vessels. In human esophagus the number and diameter of the vessels in the submucous venous plexus decrease from proximal to distal. In the stomach the subepithelial capillary network shows a honey-comb pattern reflecting the arrangement of the gastric pits. A local portal system between the gastric glands and the surface mucosal cells for the transport of HCO3- ions has been suggested. In the small intestine of humans and rabbits the existence of a dual blood supply of the villus has meanwhile been established. It consists of pericryptal capillaries for the lower portion of the villus (tuft pattern) and a direct arterial supply up to the villus tip (fountain pattern). The colonic microvasculature closely resembles that of the stomach. In the pancreas the insulo-acinar portal system is physiologically significant in that it connects the venules draining the islets with the acini. Venous sphincters in the vascular system of the exocrine pancreas of the rat are of particular functional importance. The hepatic sinusoids are supplied both by the hepatic artery and the branches of the portal vein. The peribiliary plexus is supplied by the afferent vessels of the hepatic artery, the efferent vessels drain the plexus either into the sinusoids or into the lobular vein

Microvascularization of the Pleura in Rats and Guinea Pigs

The microvascularization of the visceral and parietal pleura was studied in rats and guinea pigs using vascular corrosion casts and scanning electron microscopy. The visceral pleura was shown to be devoid of a vascular bed of its own. The capillary meshwork observed on the surface of the lung belongs to the pulmonary parenchyma. The parietal pleura, by contrast, possesses its own capillary network with an appropriate arterial supply and a venous drainage. The parietal pleural capillaries cover the costal regions completely, whereas the intercostal spaces are only provided by interspersed small patches of capillaries. That the feeding arteries of the parietal pleura are connected to the systemic circulatory system, supports the well-known fact that the parietal pleura is the main site for production of pleural fluid

The Microvasculature of the Guinea Pig Ureter. A Scanning Electron Microscopic Investigation

In 24 albinotic guinea pigs (Cavia porcellus) the gross vasculature and the microvascular architecture of the ureter were studied by light microscopy of tissue blocks and by scanning electron microscopy of vascular casts. The guinea pig ureter is supplied by the renal artery proximally, by the aorta and the internal iliac artery in its mid-segment, and by the uterine and prostatic as well as by the vesical arteries distally. The main arterial trunks run alongside the ureter before they branch to send perforating arterioles to the muscular coat and the mucosal lining. The draining venules are found on both sides of the ureter and form transverse anastomoses. Communications between the arterioles are also located on both sides, but longitudinally arranged. The capillary network of the mucosal lining shows an undulating pattern with tortuous vessels and lies just below the epithelium. The muscular coat and the adventitia have no prominent capillaries of their own. Large arteries are embedded in the adventitia, large veins in the lamina propria. In analogy to human anatomy the vascular arrangement found suggests that, if the ureters are excised in transplant surgery, a lateral incision should be used for the abdominal portion, while the pelvic portion is best approached by a medial incision

Esophageal Vasculature in the Guinea Pig: A Scanning Electron Microscope Study of Vascular Corrosion Casts

The esophageal vascularization of adult male and female albinotic Guinea pigs (Cavia porcellus) is studied by means of light microscopically evaluated serial sections and by scanning electron microscopy (SEM) of vascular corrosion casts. Bronchoesophageal artery (cervical portion), direct branches of tha aorta, recurrent branches of the intercostal arteries (thoracic portion) as well as of the left gastric artery (abdominal portion) supply the esophagus; internal jugular vein, inferior thyroid vein (cervical portion), azygos vein, intercostal veins (thoracic portion) and portal vein, gastroepiploic vein and cranial pancreatoduodenal vein (abdominal portion) drain it. Longitudinally arranged arterioles, venules and capillaries lying at the level of the lamina propria of the esophageal mucosa around the whole circumference of the organ are the most striking vascular features, whereby the venules are considered as those vessels from which esophageal varices arise under pathological conditions

Sphincters in the Rat Pulmonary Veins. Comparison of Scanning Electron and Transmission Electron Microscopic Studies

The microvasculature of the rat lung was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of vascular corrosion casts and tissue sections. Particular emphasis was placed on postcapillary venules, pulmonary venules and small pulmonary veins (small interlobular veins). Casts of lung capillaries appeared inconspicuous with smooth surface. On the casts of pulmonary venules and small pulmonary veins, by contrast, series of narrow annular constrictions, present at regular distances of 20-25 μm, were seen. These constrictions may be drastic, narrowing down the caliber of the vessel up to 50%. In the constrictions the marks of circularly running tubular structures were seen and were interpreted as being caused by circular bands of smooth muscle cells. Tissue sections of the corresponding vascular wall showed the presence of single or grouped smooth muscle cells which regularly formed myoendothelial junctions. These smooth muscle cells are interpreted as sphincters, responsible for the constrictions seen on cast preparations. Axon terminals were not found in spatial relationship to these sphincters. It is suggested that the described venous sphincters are governed by blood-borne and/or endothelium-derived substances and may significantly influence the blood flow