Circulatory pathways in the sinusal spleen of the dog, studied by scanning electron microscopy of microcorrosion casts

Scanning electron microscopy of microcorrosion casts was used to visualize circulatory pathways in the sinusal spleen of dog. The examination of contracted versus dilated organs and variations of the volume of material injected gave an indication of flow dynamics. Minimal injections of material into contracted spleens produced filling of mainly the fastest routes for flow, whereas injections into dilated spleens primarily filled slower routes. This procedure yielded a more complete, three-dimensional picture of the arterial, intermediate, and venous pathways as a whole, and of the relative amounts of flow through different arterial routes. Evidence of flow from capillary lumina out into ellipsoid sheaths was plentiful in casts from dilated spleens, but rare in casts from contracted organs. The pattern of flow within and out of the marginal sinus has been elucidated: A circumferential filling occurs first, followed by a flow that radiates outward into the marginal zone and red pulp. Venous sinuses filled via two routes in addition to the generally accepted path from the reticular meshwork via fenestrations in sinus walls. First, many venous sinuses extending out from the marginal sinus and surrounding marginal zone originated as open-ended tubes continuous with the reticular spaces of the marginal sinus or marginal zone. Second, direct connections of arterial capillaries with venous sinuses in the red pulp were found. Evidence indicating that some mechanism is controlling the flow via these routes is discussed. The strikingly different arrangement of venous sinuses in the subcapsular region is demonstrated.     

Healing of microvascular arterial anastomoses, as seen on corrosion casts by scanning electron microscopy.

We made 44 microsurgical anastomoses in the femoral artery in rats. The healing was studied from one day to 4 months, by making an acrylic cast of the lumen of the femoral artery and the surrounding vessels, and examining the cast by scanning electron microscopy. The method proved to be easy and relatively quick, and it limited the possibility of artifacts. The high depth of focus permitted simultaneous study of the main lumen and of the perivascular structures after microvascular anastomoses.     

Microvascularization of the spleen in larval and adult Xenopus laevis: Histomorphology and scanning electron microscopy of vascular corrosion casts

Microvascular anatomy and histomorphology of larval and adult spleens of the Clawed Toad, Xenopus laevis were studied by light microscopy of paraplast embedded serial tissue sections and scanning electron microscopy (SEM) of vascular corrosion casts (VCCs). Histology showed i) that white and red pulp are present at the onset of metamorphic climax (stage 57) and ii) that splenic vessels penetrated deeply into the splenic parenchyma at the height of metamorphic climax (stage 64). Scanning electron microscopy of VCCs demonstrated gross arterial supply and venous drainage, splenic microvascular patterns as well as the structure of the interstitial (extravasal) spaces representing the “open circulation routes.” These spaces identified themselves as interconnected resin masses of two distinct forms, namely “broccoli‐shaped” forms and highly interconnected small resin structures. Arterial and venous trees were clearly identified, as were transitions from capillaries to interstitial spaces and from interstitial spaces to pulp venules. Venous sinuses were not diagnosed (nonsinusal spleen). The splenic circulation in Xenopus laevis is “open.” It is hypothesized that red blood cells circulate via splenic artery, central arteries, penicillar arteries, and red pulp capillaries primarily via “broccoli‐shaped” interstitial spaces, pulp venules and veins into subcapsular veins to splenic veins while lymphocytes circulate also via the interstitial spaces represented by the highly interconnected small resin structures in vascular corrosion casts. In physiological terms, the former most likely represent the fast route for blood circulation, while the latter represent the slow route. J. Morphol. 277:1559–1569, 2016. © 2016 Wiley Periodicals, Inc.     

Luminal morphology of small arterial vessels in the contracted spleen,studied by scanning electron microscopy of microcorrosion casts

Unique luminal configurations exhibited by small arterial vessels in contracted spleens of dog and cat were studied by means of vascular corrosion casts examined by scanning electron microscopy. Concertina-like pleating was seen in casts of trabecular arteries/arterioles, whereas within lymphatic nodules arteriolar casts lacked pleating and were smooth and uniformly cylindrical (as were all small arterial vessels in distended spleens). Morphological details of arterial vessels observed in histological sections indicated that pleating is not due to contraction of specially arranged vascular smooth muscle but to overall shortening of trabecular arterial vessels, caused by contraction of longitudinal smooth muscle in trabeculae. Another phenomenon observed in casts from contracted spleens was an almost complete "pinching-off" of many arteriolar lumens; histological evidence indicated that this is due to contraction of vascular smooth muscle, which selectively diverts flow away from certain regions of the organ. Also noted was a markedly convoluted, tortuous configuration of arterioles (penicilli) in the red pulp of contracted spleens.     

The intermediate circulation in the nonsinusal spleen of the cat, studied by scanning electron microscopy of microcorrosion casts

Scanning electron microscopy of microcorrosion casts was used to visualize circulatory pathways of the intermediate circulation in nonsinusal spleen of cat. The marginal sinus (MS) around lymphatic nodules is a distinct vascular space which fills preferentially before the filling of the marginal zone (MZ) and surrounding red pulp occurs. The MS, which has a plentiful vascular supply, does not usually enclose the nodule completely. From the MS, flow occurs radially outwards into the MZ. Corrosion casts and histological sections both showed that a diversity of forms of the MZ exists: The thickness of MZ and the arrangement of its reticulum vary among nodules and between different areas of the same nodule, from a complete absence to a region of up to 50 microns in width. No direct arteriovenous connections were found (in contrast to dog spleen: Schmidt et al., '83b). Aside from capillary endings in the MS and MZ, all arterial capillaries terminate in the reticular spaces of the red pulp, i.e., the circulation appears to be entirely "open." From each capillary termination a great variety of flow pathways through the reticular meshwork to the pulp venules is available; some of these routes are quite long but others may involve distances as short as 15-25 microns. Evidence of flow into ellipsoid sheaths was abundant in casts from dilated spleens, but scarce in contracted spleens. In contrast to the extensive system of interconnected venous sinuses in dog spleen, the pulp venules found in cat spleen are nonanastomosing, shorter, and much smaller in caliber, and all receive flow freely from the reticular meshwork via open ends and fenestrations in their walls.     

Direct arteriovenous connections and the intermediate circulation in dog spleen,studied by scanning electron microscopy of microcorrosion casts

Summary The exact nature of the circulatory pathways in dog spleen, particularly with reference to the intermediate circulation and the possible existence of direct arteriovenous connections, has been studied by scanning electron microscopy (SEM) of microcorrosion casts. A new casting procedure was developed in which minimal amounts of material were injected into contracted spleens, thus filling preferentially the faster channels for flow. Extensive filling of the red pulp was thereby avoided, leaving an open view of blood vessels and their connections. The depth of focus of the SEM, incomparably greater than those of transmission electron or light microscopes, enabled vascular pathways to be traced over considerable distances.Using this approach, we have obtained clear evidence for abundant connections between arterial capillaries and venous sinuses (i.e., closed circulation). Typically, the terminal arteriole bifurcates repeatedly, in quick succession, giving rise to as many as twelve short capillaries, each leading directly to at least one sinus. However, an open circulation also exists, inasmuch as the majority of all capillaries end in the marginal zone around lymphatic nodules. In the dilated spleen, direct connections to sinuses are rarely visible but endings in the red pulp are found, in addition to those going to the marginal zone.     

Microvasculature of the bear heart demonstrated by scanning electron microscopy

Morphological features of the coronary microvasculature were examined in ten Black bears (Ursus americanus). Tissue samples were collected for scanning electron microscopy from five animals, and vascular casts of the coronary vessels were prepared from five. Each portion of the microvasculature examined had specific morphological characteristics which may contribute to the control of blood flow. All indications from the present study suggest that the structure of the coronary microvasculature in the Black bear is similar to that of mammalian species previously examined.     

The angioarchitecture of estrous, pseudopregnant and pregnant rabbit ovary as seen by scanning electron microscopy of vascular corrosion casts

Ovarian angioarchitecture was studied by scanning electron microscopy of vascular corrosion casts in estrous, pseudopregnant (stimulated with human chorionic gonadotropin) and pregnant rabbits. In all samples, the proper ovarian branch of the ovarian artery (ramus ovaricus) entered the ovarian hilus near the caudal pole of the organ and ran parallel to the major axis of the hilus. The extraovarian venous drainage was formed by several vessels emptying into a distal large vein. The ramus ovaricus exhibited various degrees of coiling and branched in the medulla. The coiling of the ramus ovaricus and its ramifications were maintained in all samples. A venous meshwork and/or flat vein branches closely enveloped the arterial coils found in the hilus and outer medulla. At this level numerous arteriovenous contacts were demonstrated in all samples. The coiled arteries, prior to entering the ovarian cortex, supplied several small peripheral follicles which were drained by the hilar veins. In the cortex the coiled arteries branched in numerous thin, straight or slightly undulated arterioles which supplied developing estrous follicles and pseudopregnant corpora lutea. The arterioles supplying the pregnant corpora lutea were long, large and tightly spiraled. The venous drainage followed the modifications of the arterial supply. These data demonstrate that ovarian cycle and pregnancy induced significant changes in the cortical vessels, which adapted their structure to the temporary functional needs of the recruited follicles or corpora lutea. Hilar and medullary vessels have permanent structures that may represent morphological devices for (a) a continuous control of the blood flow (spiral arteries) and (b) a local recirculation of endocrine products (arteriovenous contacts) comparable to the ”countercurrent mechanism” previously shown to operate in ovaries of other species, but not yet found in rabbits. Received: 19 June 1996 / Accepted: 7 October 1996     

Development of the vascular bed in the rabbit ear: scanning electron microscopy of vascular corrosion casts

The development of the vascular bed in the rabbit ear was investigated using vascular corrosion casts from animals of various ages. Examination of the casts revealed that the arrangement of the major auricular arteries and veins was determined before birth and was maintained during postnatal growth of the ear. Furthermore, the number of arteries branching off the central ear artery and the lateral arteries did not increase with increasing ear length. Scanning electron microscopic examination of lateral segments of adult ear casts revealed many anastomoses between marginal arteries and veins. These arteriovenous anastomoses (AVAs) occurred singly, in pairs, or in clusters of three to six. Their size and shape were variable, even in the same cast. The central segment of many AVA casts showed surface impressions of endothelial cell nuclei which were different from the impressions on adjacent arteries and veins. Arteriovenous anastomoses were also detected in ear casts from animals as young as 8 days. The density of AVAs in lateral ear segments ranged from 95-165 cm-2 in 8- to 11-day-old rabbits to 80-115 cm-2 in adults. However, estimates of the total number of AVAs in the lateral ear margin indicated that AVAs continued to be formed at a steady rate during growth of the ear. During the early neonatal period the cutaneous capillary plexuses developed prominent tufts projecting toward the skin surface, which were apparently associated with developing hair follicles. These capillary tufts were not seen in casts from fetal or adult rabbits.     

A scanning electron microscopy study of vascular casts from senile human brains.

A scanning electron microscope study was performed of vascular casts from 26 senile human brains. In 15 of these, three types of arterial deformities (glomerular loop formations, vascular wickerworks and bundles) were frequently encountered. They were compared with the appearance in microangiograms and histological sections.     

The vasa nervorum: microcorrosion casts for scanning electron microscopy

Studies on the vasa nervorum have a long history, not least because of their beneficial application in surgical practice and in understanding the pathogenesis of some neuropathies. In the present study a method is described for the preparation of microcorrosion casts of the vasa nervorum suitable for examination by scanning electron microscopy. The results confirm the findings of earlier investigations but also demonstrate the advantages of an immediate three-dimensional representation of the vascular architecture together with the additional magnification and resolving power of electron microscopy.     

Hypophyseal angioarchitecture of common tree shrew (Tupaia glis) revealed by scanning electron microscopy study of vascular corrosion casts.

The vascular corrosion cast technique in conjunction with scanning electron microscopy (SEM) was used for the study of pituitary microvascularization in the common tree shrew (Tupaia glis). The pituitary vascular casts were obtained by infusion of low viscosity methyl methacrylate plastic (Batson's no.17) mixture. It was found that the blood supplies to the pituitary complex were from branches of the circle of Willis and could be divided into two groups. The first group consisted of two to four superior hypophyseal arteries (SHAs) branching off from the internal carotid artery supplying each half of the median eminence (ME), infundibular stalk (IS), and pars distalis (PD). The SHAs supplying the ME branched into internal and external capillary plexi. The internal plexus had a larger capillary size (approximately 15 microns in diameter), was deeper in position, and had denser and more complex capillary loops than those in the external plexus. The capillaries of the external plexus were approximately 10 microns in diameter. The two plexi drained into 15-20 hypophyseal portal veins (HPVs) which were located mainly along the ventral and ventrolateral surfaces of the IS before breaking up into large capillaries (approximately 18 microns in diameter) with an anteroposterior arrangement within the PD. The second group consisted of one inferior hypophyseal artery (IHA) on each side branching off from the internal carotid artery. These arteries gave off branches to pierce the dorsolateral and ventrolateral aspects of infundibular process (IP) before branching off to form a capillary network. They also gave rise to radiating capillaries to supply the pars intermedia (PI) surrounding the cortical area of the IP. The hypophyseal cleft separating the PI from the PD was clearly seen with very few blood vessels. The capillaries in both PD and IP joined to form confluent hypophyseal veins draining the blood into the cavernous sinus.     

Pancreatic microcirculation in the common tree shrew (Tupaia glis) as revealed by scanning electron microscopy of vascular corrosion casts.

Pancreatic vascular casts of the common tree shrew (Tupaia glis) were prepared by infusion of Batson's No. 17 plastic mixture into the blood vessels and examined by scanning electron microscopy (SEM). Routine histological study of the pancreas was also performed. It was found that the A and D cells appeared to occupy the core whereas the B cells were found at the periphery of the islets of Langerhans. With SEM, the insular arteriole, a branch of the interlobular artery, was shown to penetrate deeply into the core of the islets before branching off into the glomerular capillary network supplying the islets. These capillaries reunited at the periphery of the islets to become vasa efferentia and then gave off capillaries to anastomose with those in the exocrine part of the pancreas, the insuloacinar portal system. Such an insuloacinar portal system found in the pancreas of the tree shrew was similar to that found in the horse and monkey. However, there were some intralobular arterioles which did not end in the islets but directly branched into the interacinar capillary network and periductular plexus. The capillaries in the exocrine part not only gathered into intralobular venules which confluently formed the interlobular vein but also supplied the duct system. The periductular plexus also collected blood into the intralobular venule and interlobular vein, respectively.     

Microvasculature of the mouse eye: Scanning electron microscopy of vascular corrosion casts

Purpose

For drug safety assessment, ophthalmic fundus examination is of diagnostic importance in experimental animals. Interim blood samples are usually collected from the orbital venous sinus in the mouse. This report characterizes the angioarchitecture of the mouse eye.

Methods

In 10 mice, the microvasculature of the eyes of was investigated using scanning electron micrographs of corrosion casts.

Results

The mouse eye was characterized as having a rich vasculature with many thick retinal arteries and a well-developed orbital venous sinus. The eye receives its primary blood supply from the external ophthalmic artery, which is divided into three branches: the central retinal artery, as well as the medial and lateral long posterior ciliary arteries. The central retinal artery is divided into 8-9 radiating retinal arteries. The mouse has an orbital venous sinus around the orbit rather than a well-developed orbital venous plexus in the retrobulbar space as is in the rat. The orbital venous sinus is formed by the episcleral veins, the ophthalmic vein, the superior palpebral vein, inferior palpebral vein and numerous anastomotic veins among these veins.

Conclusions

The mouse ocular vasculature is quite similar to that of rats. It is recommended that the best location for insertion of a capillary tube for collecting blood is in the lateral canthus around the eye where the sinus is larger and is most readily accessible. Functional significance of the vascular patterns of the eye is discussed.     

Renal vasculature of the trout demonstrated by scanning electron microscopy, compared with canine glomerular vessels.

In order to gain additional information regarding renal circulatory patterns, we have used both ink and resin injections to study the arterial supply to the mesonephric kidney of trout. Arterial injections through the dorsal aorta with ink were made for histological preparations in which the length, termination and relationship of glomerular vessels were examined. Similar injections with methyl methacrylate were made in preparation of corrosion casts to provide us with gross replicas of the aortic branches to the kidney as well as casts of glomerular structure for scanning electron microscopy. The sequence of vessels through which arterial blood passed to the renal corpuscle and ultimately to the uriniferous tubules was traced. Each afferent arteriole was found to terminate in three to six branches which formed anastomosing circuits of capillaries; these vessels reunited at the hilum to form a single efferent arteriole. The efferent arterioles in trun traveled a short distance to peritubular capillary beds and sinusoids. Morphological evidence was found for preglomerular sphincter-like action only. The glomerular vessels were found to be similar to, although less complex than, those of the outer and mid-cortical regions of the dog kidney.     

The vasculature of Octopus arms: A scanning electron microscope study of corrosion casts

Summary Vascular corrosion casts of the brachial circulation in Octopus were observed under the scanning electron microscope. The angioarchitechture, particularly of the smaller vessels, was revealed with a clarity not previously attained. The casts are very similar in appearance with those obtained from vertebrate tissues, emphasizing the convergent development of the closed system in the two groups, and form a useful basis for further study of vascular structure and function in Octopus.The casting materials were kindly made available by Dr. B. Gannon of Flinders University, South Australia, in whose laboratory the cannulations were performed with the invaluable assistance of Mr. P. Rogers. I also thank Dr. K. Bartusek of the Electron Optical Centre, University of Adelaide, for his assistance with the electron microscopy