Microvascular anatomy of testes in the adult pipid frog,Xenopus laevis Daudin: A scanning electron microscopic study of vascular corrosion casts

The three-dimensional microvascular anatomy of the testes of adult Xenopus laevis was studied by scanning electron microscopy of vascular corrosion casts. Results showed that testicular arteries branch off from urogenital arteries and approach the testes via the mesorchium. At the dorsal surface of testes, arteries course towards the medial and lateral surfaces of the ovoid testes, pierce the tunica albuginea and run in the subalbugineal space and then penetrate the testicular parenchyma. In the parenchyma, they branch in all directions. At sites where larger branches arise, sphincters are present. Intimal cushions are found at the origin of smaller branches. Terminal arterioles capillarize and form a wide-meshed capillary network around convoluted seminiferous tubules. Inter- and peritubular capillaries cannot be differentiated reliably. Arterio-venous transition distances are short. Arterio-arterial anastomoses and veno-venous anastomoses are present. Testicular venules empty into a venous subalbugineal plexus which shows veno-venous anastomoses of different lengths and calibres. Signs of the ongoing non-sprouting angiogenesis, particularly intussusceptive branch remodelling, reflect the dynamics of the testicular parenchyma. The present study is the first that demonstrates the testicular microvascular anatomy in an anuran species and shows that X. laevis and men share the intricate convoluted seminiferous tubules with associated vascular patterns as a feature in common.     

Renal microvasculature in the adult pipid frog,Xenopus laevis: A scanning electron microscope study of vascular corrosion casts

We studied the opisthonephric (mesonephric) kidneys of adult male and female Xenopus laevis using scanning electron microscopy (SEM) of vascular corrosion casts and light microscopy of paraplast embedded tissue sections. Both techniques displayed glomeruli from ventral to mid-dorsal regions of the kidneys with single glomeruli located dorsally close beneath the renal capsule. Glomeruli in general were fed by a single afferent arteriole and drained via a single thinner efferent arteriole into peritubular vessels. Light microscopy and SEM of vascular corrosion casts revealed sphincters at the origins of afferent arterioles, which arose closely, spaced from their parent renal arteries. The second source of renal blood supply via renal portal veins varied interindividually in branching patterns with vessels showing up to five branching orders before they became peritubular vessels. Main trunks and their first- and second-order branches revealed clear longish endothelial cell nuclei imprint patterns oriented parallel to the vessels longitudinal axis, a pattern characteristic for arteries. Peritubular vessels had irregular contours and were never seen as clear cylindrical structures. They ran rather parallel, anastomosed with neighbors and changed into renal venules and veins, which finally emptied into the ventrally located posterior caval vein. A third source of blood supply of the peritubular vessels by straight terminal portions of renal arteries (vasa recta) was not found.     

Microvascular anatomy of the esophagus in larval and adult Xenopus laevis Daudin: a scanning electron microscope study of microvascular corrosion casts and correlative light microscopy

Larval to adult microvascular anatomy of the esophagus was studied in the South African Clawed Toad, Xenopus laevis (Daudin) by scanning electron microscopy of vascular corrosion casts and correlative light microscopy of paraplast embedded stained tissue sections. Analyses of vascular corrosion casts of tadpole esophaguses at premetamorphosis revealed a wide‐meshed, but mature looking capillary bed which during following prometamorphosis increased in density and gained the adult‐like pattern during late metamorphic climax by sprouting and nonsprouting angiogenesis. In adult Xenopus, the esophageal mucosa possessed a dense subepithelial capillary bed fed by one or two esophageal arteries that originated from right and/or left thoracic aorta just distal to the origin of the subclavian arteries. In the adult undistended esophagus, esophageal arteries revealed an undulating course, a pattern that guarantees a continuous blood supply when the esophagus is extremely wide expanded as it is the case when adult Xenopus swallows large prey.     

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.     

Microvascular anatomy and histomorphology of extrapulmonary bronchi in adult Xenopus laevis Daudin (Lissamphibia; Anura) point to a role in aerial gas exchange – histomorphology of tissue sections and scanning electron microscopy of vascular corrosion casts

Studies on the amphibian respiratory tract microvascular anatomy are few. Using scanning electron microscopy (SEM) of vascular corrosion casts (VCCs) and light microscopy of perfusion‐fixed tissue sections, we studied the bronchial microvascular anatomy in the adult South African Clawed Toad, Xenopus laevis Daudin. Histomorphology showed that the bronchial wall consists (from luminal to abluminal) of squamous epithelium, subepithelial capillary bed, cartilage rings or cartilage plates, a layer of dense connective tissue, a layer of smooth muscle cells, and squamous epithelium (serosa). SEM of VCCs reveals that bilaterally a ventral, a dorsal (Ø 77.21 ± 7.61 μm), and a caudal bronchial artery supply the bronchial subepithelial capillary bed. The ventral bronchial artery has 3–4 branching orders (interbranching distances: 506.3 ± 392.12 μm; branching angles of first‐ and second‐order bifurcations: 24.60 ± 10.24° and 29.59 ± 14.3°). Casts of bronchial arteries display imprints of flow dividers and sphincters. Cranial and caudal bronchial veins (Ø 154.78 ± 49.68 μm) drain into pulmonary veins. They lack microvenous valves. The location of the dense subepithelial capillary meshwork just beneath the thin squamous bronchial epithelium and its drainage into the pulmonary veins make it likely that in Xenopus, bronchi assist in aerial gas exchange.     

Microvascularization of the thyroid glands in larval and adult Xenopus laevis‐ histomorphology and scanning electron microscopy of vascular corrosion casts

This study demonstrates gross arterial supply, venous drainage and microvascular patterns of larval and adult thyroid glands in the African Clawed Frog, Xenopus laevis by scanning electron microscopy of vascular corrosion casts and light microscopy of stained serial tissue sections. Results confirm published findings gained by microscopical dissections with respect to gross arterial supply. However, in adult frogs one rather than two thyroid veins are found. This study reveals for the first time that bilaterally located thyroid glands in premetamorphosis have immature capillary networks, lack a clear hierarchy of blood vessels, and show many signs of sprouting angiogenesis. During metamorphic climax, blood vessels gain a clear hierarchy and capillaries form closed networks around thyroid follicles. From climax onwards, non‐sprouting angiogenesis (intussusceptive microvascular growth) becomes the prevailing mode of angiogenesis intensifying follicle capillarization. Due to narrow interfollicular spaces, thyroidal arterioles remain superficial while draining venules are located interfollicularly. In contrast with the mammalian thyroid gland where most thyroid follicles have their own capillary beds, most thyroid follicles in Xenopus share their capillary beds with neighbouring follicles. Consequently, the concept of individual morphological and functional angiofollicular units applicable to adult mammalian and human thyroid glands is not applicable to larval and adult amphibian thyroid glands.     

Microvascularization of the interhyoid muscle in larval Xenopus laevis (Daudin): Scanning electron microscopy of vascular corrosion casts and correlative light microscopy

The interhyoid muscle in tadpoles of Xenopus laevis (Daudin) is an important part of the buccal pump, a functional unit that provides unidirectional flow of water through mouth and pharynx. In anuran tadpoles, this flow is crucial in both respiration (gas exchange) and food intake (ingestion). The microvascular anatomy of the interhyoid muscles of 43 tadpoles of X. laevis from developmental stages 49–60 was examined by scanning electron microscopy of vascular corrosion casts and correlative light microscopy of paraplast embedded Goldner stained serial tissue sections. Analysis of vascular corrosion casts of the interhyoid muscle showed that several descending branches of external carotid arteries supplied the interhyoid muscle. Arteries splitted into many arterioles at the dorsal surface of the interhyoid muscle and formed sheaths of longitudinally orientated capillaries around muscle fibers. Postcapillary vessels formed perpendicularly orientated arrays of collecting venules (mean diameter: 15.6 μm), which drained the interhyoid muscle from the ventral surface into external jugular veins. Cast analyses revealed sprouting angiogenesis at the capillary level and nonsprouting angiogenesis at distal domains of the venous system. Both means of angiogenesis that persisted throughout the developmental periods examined are thought to represent a superposition of concurrent developmental and physiological processes. The dense microvascular bed of the interhyoid muscle reflects its high demand for supply with oxygen and nutrients. J. Morphol., 2011. © 2010 Wiley‐Liss, Inc.     

A morphometric study of bone and tooth volumes in the pipid frog Xenopus laevis (Daudin), with comments on the importance of tooth resorption during normal tooth replacement

Volumetric estimations of teeth and bone on serial sections using a semiautomatic image analyzer indicate that, in the polyphyodont dentition of the pipid anuran Xenopus laevis (Daudin), the mean volume of the dentine composing the teeth is about 23.5% of the volume of the supporting maxillae and premaxillae. During tooth replacement, osteoclasts resorb up to 98% of the dentine. Teeth may be resorbed rather than shed in order to conserve tooth constituents because, if shedding of complete teeth did occur, a quantity of calcified tissue equal to perhaps 45 times the volume of the bone of the upper jaw might be lost over an animal's projected life span of about 13-15 years.     

Microvascular architecture of the pampiniform plexus-testicular artery system in the rat: a scanning electron microscope study of corrosion casts

Because the architectural and biochemical properties of skeletal muscle dictate its force, velocity, and displacement properties, the major extensors (triceps brachii) and flexors (biceps brachii, brachialis, and brachioradialis) of the elbow in a primate (cynomolgus, monkey) were studied. Functional cross-sectional areas (CSA) were calculated from muscle mass, mean fiber length (normalized to a 2.20 microns sarcomere length), and angle of fiber pinnation measurements from each muscle. Fiber-type distributions were determined and used as a gross index of the biochemical capacities of the muscle. The extensor group had a shorter mean fiber length (31 vs. 47 mm), a larger CSA (13 vs. 8 cm2), and a higher overall percentage of slow-twitch fibers (47 vs. 26%). Consequently, the elbow extensors had a relatively greater potential for force production and force maintenance than the flexors. In contrast, the flexors were designed to optimize their length-velocity potentials; i.e., they had relatively long fibers and a higher fast-twitch fiber composition than the extensors. These morphologic differences between antagonistic muscle groups should be considered when evaluating the motor control mechanisms regulating reciprocal movements about the elbow.     

The Vascularization of the Anuran Brain Rhombencephalon and Medulla spinalis: A scanning electron microscopical study of vascular corrosion casts

Albrecht, U., Lametschwandtner, A., Adam, H. 1980. The vascularization of the anuran brain. Rhombencephalon and medulla spinalis. A scanning electron microscopical study of vascular corrosion casts. (Department of Zoology, University of Salzburg, Austria.) — Acta zool. (Stockh.) 61 (4): 239–246. The vascularization of the rhombencephalon and the medulla spinalis of Bufo bufo (L.) is demonstrated by scanning electron microscopy of vascular corrosion casts. The arterial supply of the rhombencephalon is performed by central arteries. The same is shown in the medulla spinalis. The venous pathways are represented by venae craniales occipitales and by a posterior and bulbar group of the encephaloposthypophysial portal vein, by veins draining into the venae craniales occipitales, by venae spinales ventrales (for the rostral regions of the medulla) and by venae spinales laterales (in the caudal medulla). In the regions examined so far a centrifugal course of the arterial vessels is reported.     

The Vascularization of the Anuran Brain Diencephalon and Choroid Plexus: A scanning electron microscopical study of vascular corrosion casts

Albrecht, U., Lametschwandtner, A., Adam, H. 1979. The vascularization of the anuran brain. Diencephalon and choroid plexus. A scanning electron microscopical study of vascular corrosion casts. (Department of Zoology, University of Saulzburg, Austria.) — Acta zool. (Stockh.) 61(4): 203–220. The vascularization of the diencephalon (with choroid plexus of the third ventricle, epithalamus and pineal region, thalamus and hypothalamus) of the toad, Bufo bufo (L.) has been studied by means of scanning electron microscopy of vascular corrosion casts. To localize angioarchitectonic patterns of distinct diencephalic regions the authors refer to critical point dried specimens and to histological sections. In the choroid plexus a supply via one choroid artery, which arises from the posterior telencephalic artery, was found. Its strict dichotomous branching is pointed out. In generally a similar vascular pattern like that in the choroid plexus of the fourth ventricle has to be reported. Furthermore the epithalamic region with the epiphysial area was under investigation. No special angioarchitecture of the epiphysis was found. There are also no prominent vascular connections with thalamic or hypothalamic regions. The thalamic region is supplied by branches of the posterior telencephalic artery as well as by branches of the preoptic artery. Epithalamic and thalamic regions are drained via the posterior diencephalic vein. Special attention was also paid to the preoptic, the chiasmatic and the retrochiasmatic area. No special vascular connections, however, were found.     

The Vascularization of the Anuran Brain: Olfactory Bulb and Telencephalon: A scanning electron microscopical study of vascular corrosion casts

Lametschwandtner, A., Albrecht, U., Adam, H. 1980. The vascularization of the anuran brain. Olfactory bulb and telencephalon. A scanning electron microscopical study of vascular corrosion casts. (Department of Zoology, University of Salzburg, Austria.) — Acta zool. (Stockh.) 61(4): 225–238. The vascularization of the olfactory bulb and the telencephalon of the anuran brain is studied by means of scanning electron microscopy of vascular corrosion casts.—The olfactory bulb is supplied via a terminal branch of the ramus hemisphaerii medialis ventralis, while the drainage is via the lateral telencephalic vein. The vascular plexus which caps the olfactory bulb shows “basket-like” vascular formations facing the rostral olfactory bulb. This plexus is supplied via two sources which are a) terminal branches of the ramus hemisphaerii medialis ventralis and b) a branch of the inner carotid artery. — In the telencephalon the vascular pattern of medial and lateral cortex, the striatum, the septum, and the amygdala are described. It is demonstrated that in the cerebral cortex of the anuran brain the centrifugal blood flow is not present in that strictness found in the other parts of the brain. The arterial supply is via the ramus hemisphaerii medialis ventralis and the posterior telencephalic artery (ramus hemisphaerii medialis dorsalis) and their branches as well as by branches of the preoptic artery. The venous drainage of the telencephalon is by the lateral telencephalic vein.     

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.     

Thymic vascular system of the European common frog,Rana temporaria: a scanning electron-microscopic study of vascular casts

Vascular corrosion casts of the thymus of adult individuals of the European common frog, Rana temporaria, were analysed by scanning electron microscopy. The main arterial vessel, which is derived either from the temporal artery or from the auricular ramus, approaches the central territory of the gland and branches into twigs that, on penetrating the parenchyma, give rise to capillaries. Most of these capillaries run vertically towards the surface of the gland; they either join the superficial capillary plexus or follow this plexus for a variable distance and then run back towards the medulla, forming capillary loops. The former capillaries link with the extensive venous plexus composed of irregular meshes, whereas the latter capillaries join the venules at the cortico-medullary boundary and finally escape into collecting veins on the gland surface. The venous twigs, which join together near the gland, form the main thymic vein, which empties into the external jugular vein. The details of the thymic vasculature of the anuran amphibian, R. temporaria, are compared with those described in mammalian species, viz. the mouse, rat and guinea pig.     

Retinal vascularization in the grass goby,Zosterisessor ophiocephalus: a scanning electron-microscopic study of vascular corrosion casts

Synopsis The retinal vascularization ofZosterisessor ophiocephalus is described by scanning electron microscopy of vascular corrosion casts. The retina is vascularized sclerad by the choroidal body and the choriocapillaris, and vitread by the lentiform body and by a dense network of hyaloid vessels. In the bodies there is a parallel arrangement of capillaries indicating a counter current exchange mechanism. The well developed vascularization and its correlation with the hypoxic conditions of the muddy habitat of the species are discussed.     

Rhinoglena frontalis (Rotifera,Monogononta): a scanning electron microscopic study

Females and males of Rhinoglena frontalis (Monogononta, Epiphanidae) are observed by SEM and their external morphologies are compared. The two sexes differ in size and shape of the body. The female body is fusiform with a short, conical foot, while the male body is more slender and has a rather long foot. The rotatory apparatus (or corona) of both sexes is similar with only minor differences and consists of rows and tufts of cilia arranged around the mouth opening. The corona is made of two paired lobes lateral to the mouth and of a third prominent dorsal lobe, usually called proboscis. The three lobes are lined externally by dense rows of cilia, which constitute the cingulum, used for swimming. The central surface of the proboscis is covered with numerous longitudinal rows of cilia bent towards the mouth. The lateral lobes show, on their central surfaces, two concentric arcs of cirri (made of tightly packed cilia) bent towards the mouth. The similar organization of the rotatory apparatus of both sexes is related to the fact that the male, in this species, is able to feed and has a developed mastax and digestive system. The trophi of both sexes are illustrated and compared.     

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.     

Vascularization of the brains of the Atlantic and Pacific hagfishes, Myxine glutinosa and Eptatretus stouti: a scanning electron microscope study of vascular corrosion casts

The microvascularization of the brains of the hagfishes, Myxine glutinosa L. and Eptatretus stouti, were studied by scanning electron microscopy (SEM) of microvascular corrosion casts. Sections of these casts were used to determine the vascular territories of defined brain areas. Histological serial sections (10 microm) of the brains served for correlation of findings. Analysis of the microvascular casts of both species revealed that the blood supply to and from these brains arose ventrally and dorsally, respectively. Neither species possesses an arterial circle (Circulus Willisi) and both have similar microvascular patterns. The only difference between Myxine and Eptatretus was that the posterior cerebral artery in Myxine divides into mesencephalic and rhombencephalic branches, and in Eptatretus a third branch, termed telencephalic branch, arises from the posterior cerebral artery. 3D-morphometry revealed that luminal diameters of: 1) intracerebral arteries and arterioles range from 35.11 +/- 5.66 microm (mean +/- SEM) in the hypothalamus to 92.69 +/- 14.48 microm in the thalamus; 2) capillaries range from 17.8 +/- 0.44 microm in the olfactory bulb to 21.70 +/- 0.87 microm in the basal ganglia; and 3) intracerebral venules and veins range from 49.38 +/- 4.17 microm in the hypothalamus to 75.58 +/- 6.59 microm in the rhombencephalon. Interbranching distances of arteries and arterioles range from 179.19 +/- 11.32 microm in the optic tectum to 235.19 +/- 94.64 microm in the hypothalamus. Capillaries range from 91.07 +/- 6.22 microm in the hypothalamus to 116.15 +/- 9.45 microm in the thalamus, and venules and veins range from 137.30 +/- 18.11 microm in the hypothalamus to 189.83 +/- 17.47 microm in the optic tectum. Intervascular distances range from 70.58 +/- 3.58 microm in the olfactory bulb to 89.52 +/- 5.74 microm in the optic tectum. Branching angles of arteries and arterioles range from 38.39 +/- 10.9 degrees in the olfactory bulb to 100.73 +/- 9.4 degrees in the optic tectum, and the branching angles of capillaries range from 74.40 +/- 5.42 degrees in the optic tectum to 90.24 +/- 4.66 degrees in the olfactory bulb. Finally, the branching angles of the venules and veins range from 67.84 +/- 6.83 degrees in the tegmentum of the mesencephalon to 92.30 +/- 6.35 degrees in the optic tectum.     

Brain-capillary architecture of the newt,Triturus cristatus carnifex (Caudata: Salamandridae): Scanning electron-microscopical study of vascular corrosion casts

The brain-microvascular architecture of the newt (Triturus cristatus carnifex) was studied by scanning electron-microscopical examination of microvascular corrosion casts. It is characterized at the leptomeningeal level by a superficial network of single vessels that leave the meningeal sheath to form hairpin-shaped capillary loops. These loops penetrate the nervous parenchyma to varying depths and are variously bent, inclined, and twisted. Each hairpin-like loop consists of descending and ascending limbs connected by a distal U-shaped segment. The limbs are of equal diameter and lack physical differentiation. Some loops branch in a secondary loop, but there are no intraparenchymal connections with analogous surrounding structures. On vascular casts we observed detailed imprints of endothelial cell nuclei. This microvascular architecture is present in the whole brain except in leptomeninx and choroidal plexuses. The vascular pattern of T. cristatus carnifex resembles that of apodans. However, it differs from the anuran condition, which is characterized by a three-dimensional parenchymal network and from that of Ambystoma mexicanum which displays an intermediate condition between a single-capillary network and a capillary-loop model. At the level of paired capillaries, a counter-current exchange system may occur between the two limbs of the same loop, an arrangement that could promote uniformity of extracellular fluid composition in parenchyma.