Microvascular architecture of rat nasal associated lymphoid tissue

The blood vascular architecture of the rat nasal associated lymphoid tissue (NALT) was studied by scanning electron microscopy of corrosion casts. To examine the correlation of the vasculature with the distribution of lymphocyte subsets, the NALT was also studied by light microscopy of immuno-stained samples. The NALT was supplied by a branch of the inferior nasal artery which arose from the sphenopalatine artery. This branch reached the bottom of the NALT and ramified arterioles to the follicles and the parafollicular regions. These arterioles ascended toward the subepithelial region, giving off capillaries en route to form a coarse plexus within the follicles and the parafollicular regions. The arterioles reached the subepithelial region and formed a subepithelial capillary network consisting of a single layer of flat meshwork. The follicular, parafollicular and subepithelial capillaries anastomosed one another. The capillaries in each region were gathered into collecting venules, which in turn drained into high endothelial venules (HEVs) in the parafollicular region. The HEVs ran through the parafollicular regions around the follicular perimeters, and flowed into ordinary veins to leave the NALT. Lymphocytes labeled with an anti-T cell antibody were mainly distributed in the parafollicular regions, where HEVs were situated. B cells were mostly observed in the follicular and dome areas. The microvascular structure and its correlation with lymphocyte subset domains in the NALT were essentially similar to those in other mucosa associated lymphoid tissues (MALTs) such as tonsils and Peyer's patches.     

Microvascular organization of human palatine tonsils

We describe the three-dimensional organization of the microvasculature of human palatine tonsils as revealed by the vascular corrosion casting/scanning electron microscope method and light microscopy of sections. The tonsillar arteries travel in the connective tissue septa and give off many branches. They further branch into arterioles which in turn enter the follicle and the interfollicular region. These arterioles, giving off capillaries en route, reach the subepithelial region where they break up into sinusoidal capillaries. The subepithelial capillary network overlying the follicle protrudes hemispherically towards the crypt, while that overlying the interfollicular region has many switch-back loops of capillaries projected towards the crypt. The subepithelial sinusoids gather into the high endothelial venules (HEVs) which, collecting capillaries in the follicle and the interfollicular region en route, course down into the interfollicular region alongside the follicle. The HEVs surround the lateral and basal surfaces of the follicle and ultimately lead into the ordinary veins in the septa. The subepithelial sinusoids seem to be involved in taking up immunoglobulins secreted by plasma cells and any other substances released by lymphocytes and/or macrophages as well as supplying the tissues with necessary oxygen and nutrients. That the HEVs are downstream to the subepithelial sinusoids suggests that some substances which are taken up into the sinusoids and transported to the postcapillary venules induce differentiation of HEVs and maintain them.     

Blood vessels of the Peyer's patch in the mouse: I. Topographic studies

The topographic distribution of blood vessels in Peyer's patches of mice was studied by light and scanning electron microscopy with whole mounts of flattened gut segments and vascular corrosion casts. Peyer's patches are imbedded in the intestinal wall and share its blood supply. Two to four mural trunks may contribute to the area of the patch. In and around the lymphoid nodules the microcirculation is highly specialized. The nodule is permeated by a meshwork of fine capillaries that is supplied by arterioles entering on the serosal and lateral surfaces. Blood flow to the lymphoid nodule appears tobe monitored by arterial sphincters; the dense lymphatic tissue can also beby passed by arteriovenous communications. An extensive venous network encircles the nodule. Most of these venules are lined by high endothelium which is penetrated by lymphocytes. The geometry of these vessels suggests a slow and turbulent flow in these vascular segments that may aid margination of lymphocytes. A planar capillary plexus lies subjacent to the mucosal epithelium in the dome area.     

Developmental study of the anal tonsil in the laboratory shrew,Suncus murinus

The laboratory shrew, Suncus murinus, which lacks such gut associated lymph organs as the appendix and Peyer's plates, was recently demonstrated (Kubo and Isomura, 1996) to possess a pair of anal tonsils at the end of its rectum. The present paper deals with the development of this lymphoid organ as observed by light and electron microscopy. The anal tonsil was characterized by the initial postnatal development. On neonatal Day 1, a pair of epithelial crypts formed at the dorsal boundary between the anus and the ostium urogenitoanale. On Day 2 after birth, lymphocytes began to accumulate in the subepithelial mesenchymal tissue under the crypt. From Day 3 on, the lymphocytes increased to form a lymph nodule, from which, on Day 5, some lymphocytes began to penetrate into the crypt epithelium. The crypt and the nodule were fused together between Days 6 and 8. A germinal center-like structure was observed on Day 20 after birth. Around Day 40, the invading cells comprised cellular units consisting of large and small lymphocytes and plasma cells. High endothelial venules were observed in the parafollicular area at this time. These findings indicate that the anal tonsil originates from an accumulation of lymphocytes in the mesenchymal tissue close to a particular epithelium of the crypt, presumably in response to antigens in foods; the tonsilar structure is then gradually completed by fusion of the lymphoid and epithelial elements. This paper further reports on an electron microscope finding on Day 8 where the anal tonsillar crypt epithelium was seen to contain some basal-granulated cells of the open type.     

The blood vascular architecture of the salamander external gill: a scanning electron microscopic study of corrosion casts

The blood vascular architecture in three-paired external gills of salamander tadpoles, Hynobius dunni Tago, was demonstrated with special reference to metamorphosis by scanning electron microscopy of vascular corrosion casts. In the fully developed gill, each of the three-paired afferent branchial arteries gave off secondary afferent filament arterioles. The afferent filament arteriole drained toward the efferent filament arteriole, forming the loop at the posterior extremity of the gill filament. The branched capillaries from the afferent filament arteriole formed two plates of respiratory capillary networks with irregular honeycomb-shaped meshes. In addition, there were non-respiratory shunts as bypass of the blood circulation between the afferent and efferent branchial arteries without branching filament arterioles. Furthermore, the deep venous plexus and subepithelial capillary plexus were seen around each efferent branchial artery. The filament central venule in the central part of the filament merged into the venous plexus. Nutritive capillaries branched from efferent branchial arteries also drained toward the venous plexus. Such general vascular architecture is simpler than that of the fish. During metamorphosis, the pattern of the vascular distribution, especially filament net capillaries became irregular, and then markedly tortuous or convoluted blood vessels occurred in the absorbing gill. At the metamorphic climax, the capillary network practically disappeared in the remnant of the gill but the bypass shunt as a non-respiratory artery remained almost unchanged.     

扫描电镜对胎儿左心室壁内微血管构筑的观察

用血管铸型结合扫描电镜方法研究了5例胎儿左心室壁内微血管构筑。在心肌中层内,较大的微动、静脉伴行,呈“层状”分布。微动脉与微静脉的关系是:微动脉两次近似直角双叶状分支,毛细血管汇集成毛细血管后微静脉或直接以直角汇入微静脉。在心外膜下层,微动脉间吻合丰富,分出毛细血管有两种形式。在心内膜下层,微动、静脉不伴行,微静脉数目多见,而微动脉较少。毛细血管间吻合复杂。本文对不同心肌层内的毛细血管口径、间距进行了测量,并讨论了胎儿左心室壁内微血管构筑特征和微循环模式。     

The blood vascular architecture of the rat testis: a scanning electron microscopic study of corrosion casts followed by light microscopy of tissue sections

The blood vascular bed of the rat testis was studied by scanning electron microscopy (SEM) of corrosion casts and by light microscopy of tissue sections. The testicular artery penetrates the pampiniform plexus and gives rise to the intertubular arterioles. Each of these arterioles courses in the intertubular connective tissue column, and gives off intertubular and peritubular capillaries. The intertubular capillaries pass the intertubular connective tissue column, whereas the peritubular capillaries reach the peritubular connective tissue sheet. The intertubular and peritubular capillaries anastomose with each other and converge into the intertubular venules in the intertubular connective tissue columns. Thus, the blood vascular bed of the rat testis consists of hexago- or pentago-columnar capillary networks which commonly surround the seminiferous tubules. The Leidig's cells are preferentially observed in the intertubular connective tissue columns. One of the intertubular capillaries is consistently thick, and directly continues into the intertubular venules (arteriolo-venular capillary channels), which finally drain into the pampiniform plexus. These findings suggest that the male sex hormone, testosterone, as secreted by the Leidig's cells, is discharged into the intertubular capillaries and then mainly carried by the arteriolo-venular capillary channels and intertubular venules into the pampiniform plexus. This specialized drainage may ensure the presence of highly concentrated testosterone in the pampiniform plexus and allow the testosterone-exchange from the pamipiniform plexus to the testicular artery. The arteriolo-venular capillary channels may also eliminate blood congestion in the testis to enhance the efficiency of the heat-exchange mechanism between the testicular artery and pampiniform plexus. Many arterio-arterial and arterio-venous anastomoses occur, which may regulate the blood flow within the testis.     

Angioarchitecture of the coeliac sympathetic ganglion complex in the common tree shrew (Tupaia glis)

The angioarchitecture of the coeliac sympathetic ganglion complex (CGC) of the common tree shrew ( Tupaia glis ) was studied by the vascular corrosion cast technique in conjunction with scanning electron microscopy. The CGC of the tree shrew was found to be a highly vascularised organ. It normally received arterial blood supply from branches of the inferior phrenic, superior suprarenal and inferior suprarenal arteries and of the abdominal aorta. In some animals, its blood supply was also derived from branches of the middle suprarenal arteries, coeliac artery, superior mesenteric artery and lumbar arteries. These arteries penetrated the ganglion at variable points and in slightly different patterns. They gave off peripheral branches to form a subcapsular capillary plexus while their main trunks traversed deeply into the inner part before branching into the densely packed intraganglionic capillary networks. The capillaries merged to form venules before draining into collecting veins at the peripheral region of the ganglion complex. Finally, the veins coursed to the dorsal aspect of the ganglion to drain into the renal and inferior phrenic veins and the inferior vena cava. The capillaries on the coeliac ganglion complex do not possess fenestrations.     

Rearrangement of the metaphyseal vasculature of the rat growth plate in rickets and rachitic reversal: a model of vascular arrest and angiogenesis renewed.

The morphology of the metaphyseal microvasculature at the epiphysis was examined at both the light and electron microscopic level in rickets and rachitic reversal. The animals studied were normal, rachitic, and rachitic reversed at 8, 24, and 96 hours post-vitamin D administration. The overall architecture of the metaphyseal vessels was significantly altered throughout the intervals examined. In the rachitic animal, arterioles, venules, and capillaries were found adjacent to the growth plate, either directly apposed to the hypertrophic chondrocytes or separated from them by bone-forming cells. These vessels are in many ways similar to the larger arterioles and venules that normally supply the metaphyseal capillary sprouts, but in the normal growing animal are usually located 350-500 microns from the epiphyseal cartilage. The rachitic capillaries appear relatively well differentiated with a partial basement membrane and a perivascular cell lining. In early rachitic reversal, small vascular projections are induced to grow from the large diameter venules that border upon the hypertrophic chondrocytes. These vascular sprouts that invade the epiphyseal cartilage are quite undifferentiated, with no basement membrane or pericyte lining at the sprout apex and occasional abluminal endothelial cell projections. Within 96 hours, the metaphyseal microvasculature has returned to an apparently normal state with only capillaries at the cartilage-vascular interface and larger vessels (arterioles and venules) located several hundred microns deeper into the metaphysis. The sequential processes of differentiation and cessation of capillary growth followed by dedifferentiation and reinitiation of microvascular growth make the rachitic system a unique one in which to study angiogenesis.     

Rearrangement of the metaphyseal vasculature of the rat growth plate in rickets and rachitic reversal: A model of vascular arrest and angiogenesis renewed

The morphology of the metaphyseal microvasculature at the epiphysis was examined at both the light and electron microscopic level in rickets and rachitic reversal. The animals studied were normal, rachitic, and rachitic reversed at 8, 24, and 96 hours post-vitamin D administration. The overall architecture of the metaphyseal vessels was significantly altered throughout the intervals examined. In the rachitic animal, arterioles, venules, and capillaries were found adjacent to the growth plate, either directly apposed to the hypertrophic chondrocytes or separated from them by bone-forming cells. These vessels are in many ways similar to the larger arterioles and venules that normally supply the metaphyseal capillary sprouts, but in the normal growing animal are usually located 350–500 μm from the epiphyseal cartilage. The rachitic capillaries appear relatively well differentiated with a partial basement membrane and a perivascular cell lining. In early rachitic reversal, small vascular projections are induced to grow from the large diameter venules that border upon the hypertrophic chondrocytes. These vascular sprouts that invade the epiphyseal cartilage are quite undifferentiated, with no basement membrane or pericyte lining at the sprout apex and occasional abluminal endothelial cell projections. Within 96 hours, the metaphyseal microvasculature has returned to an apparently normal state with only capillaries at the cartilage-vascular interface and larger vessels (arterioles and venules) located several hundred microns deeper into the metaphysis. The sequential processes of differentiation and cessation of capillary growth followed by dedifferentiation and reinitiation of microvascular growth make the rachitic system a unique one in which to study angiogenesis.     

Blood vascular network of the rat lymph node: Tridimensional studies by light and scanning electron microscopy

Many aspects of the blood vascular network of the lymph node are unknown, and others need confirmation. We have studied the blood vasculature of rat peripheral lymph nodes by means of carbon perfusion and vascular cast corrosion techniques. At the hilus of the node, an artery gives off arterioles running in medullary cords towards the cortex. Some reach the peripheral cortex directly, branching there into slender cortical vessels. Other arterioles enter the periphery of the deep cortex units, and then head towards the peripheral cortex. Upon reaching it, they curve part way above the center of the deep cortex units and provide slender branches to the overlying peripheral cortex. Dense plexuses of capillaries arise from arterioles in the medullary cords, in the periphery of the deep cortex units, and in the outermost stratum of the extrafollicular zone of the peripheral cortex. In the cortex, the draining high endothelial venules are restricted to the extrafollicular zone and to the periphery of the deep cortex units. At the cortico-medullary junction, these peculiar venules transform into regular medullary venules which form the hilar veins. In contrast, the folliculo-nodules and center of the deep cortex units are little vascularized by a loose capillary network, while no vessels occur in the subsinus layer. These features of the node vascular network are of interest in relation to the node architecture.     

Three-dimensional organization of the perivascular glial limiting membrane and its relationship with the vasculature: a scanning electron microscope study

To examine the three-dimensional structure of the perivascular glial limiting membrane (Glm) and its relationship with the vasculature in rat/mouse cerebral cortices, serial ion-etched plastic sections were observed under the scanning electron microscope and their images were reconstructed. In the case of arterioles and venules close to the pial surface, cord-like principal processes predominantly formed the endfeet; whereas in the case of capillaries and venules, sheet-like secondary processes chiefly formed Glm. Moreover, it was found that several plate-like structures protruded from the basement membrane surrounding the arterioles to penetrate into the astrocytic somata. The perivascular Glm was formed by monolayers of astrocytic processes and/or somata irrespective of the types of blood vessel. However, the thickness of the perivascular Glm, varied greatly according to the type of blood vessel. The thickness of Glm decreased in the order of arterioles, venules and capillaries. The outer surface of the perivascular Glm was extremely irregular, and sheet-like processes arising from this Glm infiltrated into the surrounding neuropil.     

用注射复型扫描电镜方法观察足月胎儿胆囊微血管的构筑

用甲基丙烯酸甲酯铸型方法,将胎儿胆囊壁微血管制成铸型扫描电镜样品,脱水、干燥后,用EIKO IB-3型离子镀膜仪镀膜,在扫描电镜下观察。胆囊壁微血管明显分为三层,即浆膜层血管、肌层血管和粘膜层血管。其中浆膜和肌层血管与肠管壁相应层次的血管结构类似。而粘膜层血管则被分为两部分,一部分紧贴上皮细胞下,有一层丰富的毛细血管网;另一部分在固有膜内有管径粗大的静脉丛。毛细血管网与静脉丛之间直接以毛细血管相连。微动脉的数量相对较少,穿行于静脉丛之间,并逐级分支延续于毛细血管网。本文未见有动、静脉吻合。但在微动脉与静脉丛之间,常见有构成功能性毛细血管短路的毛细血管性交通支。     

Histochemical characterization of the aging microvasculature in the human and other mammalian and non-mammalian vertebrates by the periodic acid-Schiff reaction.

Prior histochemical studies with the periodic acid-Schiff (PAS) reaction have shown altered biochemical composition in a limited part of the microvasculature (MV) in aging in two species of laboratory animals. We therefore studied, with the PAS reaction, all the components of the MV in multiple tissues from various immature, adult and aged mammals, including human, and immature and aged nonmammalian vertebrates. We now demonstrate that there is an altered biochemical composition of capillaries, arterioles and venules in various tissues with aging. These are first detectable somewhat beyond half the life-span in man (greater than 45 years), marmoset (5 years) and dog (8 years) and seen in old fish, reptiles and birds. The capillary wall is increasingly PAS+; in arterioles there are focal PAS+ areas in the media which increase in size and number with age and become hyalinized masses. The non-muscular venules are increasingly PAS+ apparently due to a polysaccharide staining of connective tissue elements. These histochemical changes in the MV with aging are in the extracellular matrix and appear to be a specific manifestation of aging in vertebrates. The consequences of such changes in MV aging may be important physiologically.     

STUDY ON THE FUNCTION AND STRUCTURE OF BLOOD VESSELS OF THE SECONDARY NODULES IN LYMPH NODE

By means of the stereographic reconstruction technique, the distribution and arrangement of blood vessels in the lymphatic nodules, especially in the secondary nodules, of human and several species of experimental mammary animals were studied. As a result, it was shown that although the development of blood vessels in the secondary nodules varied with the degrees of maturation of the nodules and with the species of animals, the vascular distribution and arrangement of the lymphatic nodules were fundamentally identical among these subjects. The arterial system of the lymphatic nodules was divided into two groups; the secondary nodule arterioles and the mantle zone arterioles. Electron microscopically, the secondary nodule arterioles revealed the ultrastructure of meta-arterioles or precapillary arterioles. For the examination of the filtrating capacity of arterioles, various perfusion experiments were carried out by intra-arterial injection using various kinds of fluids. Transudation was scarcely demonstrated in the secondary nodule arterioles, and it was also noted that the capillaries and postcapillary venules developing fairly well in the mantle zone and its vicinity played an important role in plasma tansudation in lymph nodes.     

Anatomic pathway of pulmonary fluid leakage in endotoxemia induced in rats. The red blood cell packing method and its application.

The anatomic site of pulmonary fluid leakage in endotoxemia in rats was investigated using the red blood cell packing method and low-dose horseradish peroxidase as a tracer. To differentiate between arterioles and venules in a given section by light and electron microscopy, human red blood cells fixed with 4% paraformaldehyde were administered to the rat pulmonary arterial trunk at a pressure of 40 cm water. Fixed red blood cells were packed in the lumina of arteries, arterioles, and a few capillaries surrounding arterioles, while veins, venules, and almost all capillaries were void of red blood cells in the lumina. Fifteen minutes after the intravenous administration of 3 and 30 mg/kg of Escherichia coli endotoxin, extravascular leakage of horseradish peroxidase from venules (nonmuscular veins) was evident. Two hours after the intravenous injection of the same doses of endotoxin, some arterioles (nonmuscular arteries) and venules (non-muscular veins) showed extravascular leakage of horseradish peroxidase, while few capillaries showed this leakage. These results suggest that pulmonary fluid leakage occurs predominantly through venules in the early phase of endotoxemia (at 15 minutes), while the arterioles contribute to fluid leakage in addition to venules in the late phase of endotoxemia (at 2 hours).     

The microvascular architecture of the choroid plexus in fetal human brain lateral ventricle: a scanning electron microscopy study of corrosion casts

The microvascular architecture of developing lateral ventricle choroid plexus was investigated by corrosion casting and scanning electron microscopy in human fetuses aged 20 gestational weeks. The areas with different microvascular patterns corresponded to the particular parts of the mature plexus: anterior part, glomus, posterior part, the villous fringe and the free margin. In the posterior part, densely packed parallel arterioles and venules were surrounded by sheath-like capillary networks. Other areas contained compact capillary plexuses of the primary villi: the most prominent, protruding basket- and leaf-shaped plexuses were observed in the villous fringe, whilst less numerous and smaller plexuses occurred in the anterior part and glomus. The capillaries of the plexuses had a large diameter and sinusoidal dilations, and showed the presence of occasional short, blind sprouts indicative of angiogenesis. Short anastomoses between arterioles supplying the plexuses and venules draining them were only rarely observed. In the upper area of the choroid plexus, the superior choroidal vein was surrounded by a capillary network forming small, glomerular or rosette-shapes plexuses. The free margin of the choroid plexus was characterized by flat, multiple, arcade-like capillary loops. The general vascular architecture of the human choroid plexus at 20 gestational weeks seems to be similar to that of postnatal/mature plexus, still lacking, however, the complex vascular plexuses of the secondary villi.     

Distribution of oxygen tension on the surface of arterioles, capillaries and venules of brain cortex and in tissue in normoxia: an experimental study on rats

 The distribution of oxygen tension (PO₂) was studied in normoxia on the surface of arterioles, capillaries and venules of rat brain cortex, both longitudinally and in tissue radially from the wall of microvessels. Along the arteriolar tree, PO₂ decreased from 81.2±6.2 mmHg (mean±SD) on 1°A (first-order branch) arterioles to 61.5±12 mmHg on 5°A arterioles. Transmural flux of oxygen from blood to tissue increased markedly at the level of minute 4°A–5°A arterioles. At the arterial end of cortical capillaries, PO₂ averaged 57.9±10.6 mmHg, n=19, (or, in terms of blood oxygen saturation SO_2; 82±9%) and 258±19 μm downstream 40.9±11.5 mmHg, n=19, (SO₂ 59±18%). The averaged PO₂ drop on the capillaries studied was 17±9 mmHg, and the longitudinal PO₂ gradient was accordingly 0.07±0.04 mmHg/μm (SO₂ 0.1±0.06%/μm). The radial profiles of tissue PO₂ recorded near arterioles, capillaries and venules clearly demonstrated that all these microvessels supply oxygen to brain tissue. The PO₂ distribution on venules was characterized by pronounced heterogeneity. Received: 30 March 1998 / Received after revision: 28 July 1998 / Accepted: 25 November 1998