The three-dimensional ultrastructure of the collagen fibers, reticular fibers and elastic fibers: a review]

Fibrous components of the connective tissue are light-microscopically classified into three types: collagen fibers, reticular fibers and elastic fibers. The present paper reviews the three-dimensional ultrastructure of these fibrous components, mainly based on our studies by scanning electron microscopy. The collagen fibers are shaped like tapes or cords about 1 to 20 microns in diameter. Each fiber is a bundle of fibrils running roughly parallel to each other. These collagen fibrils vary in diameter from 30 to 300 nm depending on their locating area of the body, and show a repeating pattern of depressed and protruding segments on the surface. The reticular fibers consist of collagen fibrils about 20-40 nm in diameter, which run singly or in small bundles. They are usually interwoven elaborately to form thin lace-like sheets or sheaths attaching to basal laminae of such cells as epithelial, endothelial and muscular cells. These fibers are considered to play an important role not only in adhering the cells to the collagen fibers, but also in constituting the skeletal framework suitable for individual cells and tissues. The elastic fibers consist of two different components: elastin and fibrillin. Elastin forms unit fibrils of 0.1-0.2 micron thickness which are arranged in bundles or laminae specific to individual organs and tissues. Fibrillin, on the other hand, forms microfibrils about 10 nm in diameter running in or along elastin bundles. These microfibrils also form delicate networks separate from elastin components. For a comprehensive understanding of the fibrous components in the connective tissue, the author proposed categorizing them into two systems: the collagen fibrillar system as a supporting framework of tissues and cells, and the fibrillin-elastin fibrillar system for distributing stressing forces uniformly in tissues.     

大鼠不同部位疏松结缔组织撕片的制备和观察

目的　对比大鼠皮下取材和肠系膜取材制备疏松结缔组织撕片的差异;观察同一部位取材的疏松结缔组织HE染色和醛复红-亮绿-橘黄G染色差异;分析不同部位取材的疏松结缔组织两种染色方法的结果差异。 方法　Wistar大鼠腹腔注射10 g/L苔盼蓝生理盐水溶液2.5 ml,1次/d,连续3 d,分别在皮下、肠系膜取疏松结缔组织,铺片。两个部位的铺片分别采用HE染色、醛复红-亮绿-橘黄G染色。 结果　皮下取材疏松结缔组织经HE染色可见大量成纤维细胞,肥大细胞明显,巨噬细胞可见,弹性纤维和胶原纤维可见,但不明显;皮下取材疏松结缔组织经醛复红-亮绿-橘黄G染色弹性纤维呈紫红色、胶原纤维呈橙色,细胞不易着色;肠系膜取材疏松结缔组织经HE染色,可见成纤维细胞、肥大细胞、巨噬细胞明显,弹性纤维呈蓝紫色、胶原纤维呈淡红色;肠系膜取材疏松结缔组织经醛复红-亮绿-橘黄G染色,弹性纤维被染成紫红色、胶原纤维染成鲜艳的绿色,肥大细胞被染成紫红色,核呈圆或椭圆形、棕黄色,巨噬细胞清晰可见、形态不规则,胞质中可见粗大呈蓝紫色的苔盼蓝颗粒,细胞核呈圆形、棕黄色;成纤维细胞胞质无着色,核呈棕黄色。 结论　大鼠肠系膜取材制备的疏松结缔组织撕片经醛复红-亮绿-橘黄G染色能够更好的显示各种类型细胞和纤维,各结构间对比明显。     

The connective tissue and glial framework in the optic nerve head of the normal human eye: light and scanning electron microscopic studies

The arrangement of connective tissue components (i.e., collagen, reticular, and elastic fibers) and glial elements in the optic nerve head of the human eye was investigated by the combined use of light microscopy and scanning electron microscopy (SEM). Light-microscopically, the optic nerve head could be subdivided into four parts from the different arrangements of the connective tissue framework: a surface nerve fiber layer, and prelaminar, laminar, and postlaminar regions. The surface nerve fiber layer only possessed connective tissue elements around blood vessels. In the prelaminar region, collagen fibrils, together with delicate elastic fibers, formed thin interrupted sheaths for accommodating small nerve bundles. Immunohistochemistry for the glial fibrillary acidic protein (GFAP) showed that GFAP-positive cells formed columnar structures (i.e., glial columns), with round cell bodies piled up into layers. These glial columns were located in the fibrous sheaths of collagen fibrils and elastic fibers. In the laminar region, collagen fibrils and elastic fibers ran transversely to the optic nerve axis to form a thick membranous layer - the lamina cribrosa - which had numerous round openings for accommodating optic nerve fiber bundles. GFAP-positive cellular processes also ran transversely in association with collagen and elastin components. The postlaminar region had connective tissues which linked the lamina cribrosa with fibrous sheaths for accommodating nerve bundles in the extraocular optic nerve, where GFAP-positive cells acquired characteristics typical of fibrous astrocytes. These findings indicate that collagen fibrils, as a whole, form a continuous network which serves as a skeletal framework of the optic nerve head for protecting optic nerve fibers from mechanical stress as well as for sustaining blood vessels in the optic nerve. The lamina cribrosa containing elastic fibers are considered to be plastic against the mechanical force affected by elevation of the intraocular pressure. The present study has also indicated that glial cells with an astrocytic character play an important role in constructing the connective tissue framework characteristic of the optic nerve head.     

Tissue compatibility of collagen-silicone composites in a rat subcutaneous model.

Collagen-silicone composites were fabricated and tested for biocompatibility by subcutaneous implantation in rats. The silicone component consisted of addition cure or condensation cure sheets. The collagen component was either (a) a sponge layer 2 mm thick, (b) a thin film 12-20 microns thick, or (c) residual collagen bonded to or incorporated in the silicone rubber. Collagen sponges were mechanically bonded to silicone sheets, and collagen thin films and residual collagen were physically and chemically attached to epoxy-derivatized silicone sheets. Analysis of implanted samples showed that reduced capsule formation occurred around collagen sponge-silicone, compared to control silicone sheets. Only where the underlying silicone sheet, or interpenetrating silicone, was exposed to the tissue, did limited capsule formation occur. In contrast, thin capsule developed completely around silicone coated with a thin collagen film and around silicone bonded to residual collagen. Sponge-silicone composites and control silicone sheets were free of acute and chronic inflammation, except for occasional foreign body giant cells in sponge adjacent to silicone. Silicone coated with micron-thick collagen films exhibited some inflammation, but residual collagen-silicone did not. This study suggests that, to prevent capsule formation, a collagen coat must be of minimum thickness and surface coverage sufficient to prevent any contact between silicone and tissue.     

ELASTOGENESIS IN THE LIVER

It has been well established that Increase of elastic fibers Is a prominent feature In chronic liver diseases, especially in liver cirrhosis. Little is known, however, about the mechanism of the elastogenesis in liver tissue. As a result of histological examination of the pattern of elastic fiber formation in various kinds of liver diseases, it was concluded that elastogenesis in the liver tissue can be divided into two stages: first stage is proliferation of thin elastic fibers and second step Is remodeling of newly formed and preexistent elastic fibers. It seemed reasonable to conclude that the formation of thin elastic fibers was mainly related to proliferation of arteries and arterioles, from the observation of specimens, which were injected dye from the A. hepatlca. On the other hand, thick elastic fibers found in advanced liver cirrhosis, were supposed as the result of fusion and deformation of preexistent or newly formed thin elastic fibers. Chemical analysis of collagen and elastin of the liver tissues of various conditions showed that the ratio of elastin to collagen increased with the progress of liver fibrosis. These results suggested that elastic fibers in chronic liver diseases were not teleologlcally formed to some pathological condition, but were formed and accumulated as the result of some process.     

Flow loaded canine carotid artery. II. Ultrastructural changes in the subendothelial layer

To study the subendothelial layer of the flow loaded arteries, blood flow changes were produced by constructing an arterio-venous shunt between the common carotid artery and the external jugular vein using eleven adult beagle dogs. One week after operation, the subendothelial layer of the flow loaded canine carotid arteries was observed with a transmission electron microscope. In the arteries loaded by highly elevated blood flow, the subendothelial layer showed thick subendothelial space (300 to 500 nm) with multilayered basement membrane. The microfilaments and microfibrils increased significantly. There were no collagen fibers. Spindle to cylindrical elastic fibers appeared in the luminal margin of the internal elastic lamina. On the other hand, in the control arteries, the subendothelial layer was thin (about 50 nm) with scanty basement-membrane-like material. There were a few microfilaments and microfibrils, but no collagen fibers. The luminal margin of the internal elastic lamina was smooth. It is suggested that these are the wall shear stress dependent subendothelial changes, which would be partly due to the increased protein synthesis by the endothelial cells stimulated by the wall shear stress and be partly due to the wall shear dependent mechanical stress transmitted from the endothelial surface.     

A hypothetical explanation for the aging of skin. Chronologic alteration of the three-dimensional arrangement of collagen and elastic fibers in connective tissue.

To provide a morphologic basis for a better understanding of the "aging" of human skin, the authors studied the three-dimensional arrangement and chronological alterations of the fibrous components of the connective tissue using rats aged 2 weeks to 24 months with a new technique for scanning electron microscopy. These studies showed that with postnatal growth there was a dynamic rearrangement of the collagen and elastic fibers: an ordered arrangement of mature collagen bundles was attained by producing a distortion of the elastic fiber meshwork of relatively straight fibers. During adulthood, there was a subsequent tortuosity of the distorted elastic fibers coupled with an incomplete rebuilding of the elastic fiber network, laid down in a form to interlock with the collagen bundles. These changes provide a model for explaining manifestations of aged skin, such as laxity, sagging, and wrinkling. The tortuously fixed elastic fibers imply that they have been stretched and have lost their original elasticity and ability to restitute short and straight. Interlocking of both collagen and elastic fibers should disturb the two independent fibrous systems, as would normally be the case, and thus decrease tissue compliance.     

FLOW LOADED CANINE CAROTID ARTERY II. Ultrastructural Changes in the Subendothelial Layer

To study the subendothelial layer of the flow loaded arteries, blood flow changes were produced by constructing an arterio-venous shunt between the common carotid artery and the external jugular vein using eleven adult beagle dogs. One week after operation, the subendothelial layer of the flow loaded canine carotid arteries was observed with a transmission electron microscope. In the arteries loaded by highly elevated blood flow, the subendothelial layer showed thick subendothelial space (300 to 500 nm) with multilayered basement membrane. The microfilaments and microfibrils increased significantly. There were no collagen fibers. Spindle to cylindrical elastic fibers appeared in the lumlnal margin of the internal elastic lamina. On the other hand, in the control arteries, the subendothelial layer was thin (about 50 nm) with scanty basememt-membrane-like material. There were a few microfilaments and microfibrils, but no collagen fibers. The luminal margin of the internal elastic lamina was smooth. It is suggested that these are the wall shear stress dependent subendothelial changes, which would be partly due to the increased protein synthesis by the endothelial cells stimulated by the wall shear stress and be partly due to the wall shear dependent mechanical stress transmitted from the endothelial surface.     

利用醛复红染色法制作家兔皮下疏松结缔组织铺片标本

目的 探讨适用于家兔皮下疏松结缔组织铺片标本的制片方法。方法 家兔3只,分别经腹腔注射10g/L锥虫蓝生理盐水溶液10～12ml。每天1次,连续注射3d后,于第4天取皮下疏松结缔组织进行铺片。待铺片晾干后,用福尔马林-酒精固定液固定约6h。然后,分别入醛复红、核固红和伊红染色液进行染色。每步之间用自来水冲洗。最后,常规脱水、透明、封片。 结果 巨噬细胞呈不规则形,分布在纤维中间,胞质中可见粗大的锥虫蓝颗粒。细胞核呈红色。醛复红染色30～40min时,弹性纤维呈紫色或蓝紫色,胶原纤维呈浅红色。结论 该法操作步骤简单,结果稳定可靠,是制作家兔皮下疏松结缔组织铺片标本适宜的方法。     

Three-dimensional structures of uterine elastic fibers: scanning electron microscopic studies.

We report findings that demonstrate for the first time that the structure of the elastic fibers of the uterus and cervix are characteristic to these tissues. Elastic fibers of the uterine corpus and cervix were studied by scanning electron microscopy (SEM). Elastic tissues were prepared from non-pregnant human uteri and pregnant rat uteri by three different methods: extraction from the tissue homogenates, in situ digestion by autoclaving of sliced tissue, and in situ formic acid digestion of sliced tissue. In addition, in situ formic acid digestion of the glutaraldehyde-fixed uterine wall of pregnant rats was done. Under SEM, the uterine elastic fibers revealed two distinct structures--fibrils and thin sheets of elastic membranes. Isolated fibers and membranes ranged in thickness from 0.1 to 0.4 micron which is thinner than aortic elastic lamellae (1-2.5 microns in thickness). These thin sheets of elastic membranes and elastic fibrils probably allow the uterus to maintain its elasticity without exerting excess pressure on the growing fetus. Formic acid digestion of fixed uterine walls of pregnant rats preserved the structural organization of elastic tissues near in vivo conditions. In these tissues, the fibers were arranged in a honeycomb structure made up largely of membranes, although sparse fibrils were present. These elastic, membranous sheets were arranged parallel to the plane of the uterine surface and interconnected with the threads of the membranes or fibrils. In the rat uterine wall, at least 12 parallel layers of elastic sheets were present. In contrast, at low magnification, the elastic tissues in the non-pregnant human uterus had no specific architectural arrangement and exhibited a sponge-like structure. Elastic fibers of the cervix were also made up of membranes and fibrils, and these fibers were organized into fishnet-like structures. These cervical membranes had fenestrations and pits with a diameter of 3-5 microns. In these studies, the concentrations of insoluble elastin in human uteri were found to be 1.38 and 1.32-1.41% of dry-defatted tissues for uterine body and cervix, respectively. The concentrations of total collagen were 38.8 and 64.3-72.4% of dry-defatted tissues for uterine body and cervix, respectively.     

Scanning electron microscope study of elastic fibers of the loose connective tissue (superficial fascia) in the rat

A combination of intravascular resin injection and formic acid incubation was utilized to study the three-dimensional arrangement of the elastic fibers in the loose connective tissue (superficial fascia) of the rat limb by scanning electron microscopy (SEM). The cast of the microvasculature served as a scaffolding for the otherwise collapsible connective tissue. SEM study demonstrated that the elastic fibers did not form an anastomosing network but were arranged in multiple layers. The fibers in each layer lay parallel to each other but were oriented differently from the fibers in the layers on either side, thereby producing a meshwork. Each individual fiber was composed of a small bundle of discrete fibrils. Some of these component fibrils separated from the parent fiber and united with other fibers, thus producing branching. The elastic fiber either decreased or grew in size by the respective sharing or joining of these component fibrils with neighboring fibers in their respective layers. Interconnections between elastic fibers of different layers were rare. These findings may provide a morphological explanation for the characteristic function of the superficial fascia, which allows the skin and underlying muscles to have a rapid and extensive alteration in their relative positions.     

Ultrastructure abnormalities in proteoglycans, collagen fibrils, and elastic fibers in normal and myxomatous mitral valve chordae tendineae.

Normal and myxomatous chordae tendineae were studied using light and electron microscopy, to assess the alterations in the appearance and mutual arrangement of proteoglycans, collagen fibrils, and elastic fibers. Specific staining with ruthenium red and cuprolinic blue in a critical electrolyte concentration mode were used to localize proteoglycans. Fresh tissues were fixed in glutaraldehyde containing the cationic dyes and embedded into Spurr resin. Semithin sections of LR White (London Resin Co., Basingstoke, U.K.)-embedded tissue were used for histochemistry. In normal chordae tendineae, the fibrosa comprised close-packed collagen fibrils intermixed with elastic fibers. These were surrounded by a thin layer of elastic fibers and collagen fibrils, both of which were closely associated with proteoglycans. In myxomatous chordae tendineae, alterations were observed in the connective tissue. Proteoglycans were more abundant and were distributed throughout the tissue. The outermost layer was transformed into an undifferentiated electron-dense mass surrounding the central fibrosa, which contained degraded elastic fibers and collagen fibrils. Collagen fibrils had faint banding or lacked a banding pattern altogether. Spaces between collagen fibrils were occupied by abnormal proteoglycans or proteoglycan aggregates. Elastic fibers showed varying degrees of degeneration and were occasionally replaced by electron-lucent spaces containing microfibrils. Accumulation of abnormal proteoglycan was also observed around degenerated elastic fibres and collagen fibrils.     

The structure of the interalveolar septum of the mammalian lung

Light and electron microscopic examination of serial transverse sections of interalveolar septa of hamster lung have demonstrated a virtually continuous connective tissue sheet of variable thickness in the interalveolar septum. This central sheet, like connective tissue elsewhere, is composed of ground substance in which are immersed cells, collagen and elastin. A capillary network lies on each surface of this sheet. The capillary basement membrane is continuous with the central sheet but in contrast to it is thin, uniform and devoid of cells, collagen or elastin. Capillaries on one surface frequently anastomose directly through the septum with capillaries on the opposite surface. The central sheet is shown to be virtually continuous despite frequent thinning. Whenever cells, collagen or elastin occur in the interalveolar septum, it is always in the central sheet. The efficiency of this arrangement in combining optimum gas conductance with adequate mechanical support is pointed out. The central sheet is also continuous with the perivascular connective tissue cuff and thus may serve as an important route of extracellular fluid transport to the perivascular lymphatics.     

Viscoelasticity of the vessel wall: the role of collagen and elastic fibers.

The aortic wall contains collagen fibrils, smooth muscle cells, and elastic fibers as the primary load-bearing components. It is well known that the collagen fibrils bear loads in the circumferential direction, whereas elastic fibers provide longitudinal as well as circumferential support. Stiffening of the vessel wall is associated with loss of elastic tissue and increases in the collagen content: however, little is known about the mechanism of vessel wall stiffening with age. The purpose of this review is to attempt to relate structural changes that occur to the collagen and elastic fibers to changes in the viscoelastic behavior that are associated with aging. Analysis of the viscoelastic mechanical properties of collagen fibrils from tendon, skin, and aortic wall suggest that the collagen fibrils of aortic wall are different than those of other tissues. The elastic spring constant of the collacen fibrils in vessel walls is significantly less than that found in tendon, suggesting that the presence of type III collagen in aortic wall increases the flexibility of the collagen fibrils. Furthermore, it is hypothesized that changes in the interface between collagen fibrils, elastic fibers, and smooth muscle during aging and in connective tissue disorders leads to changes in the viscoelasticity of the vessel wall.     

Skin is a window on heritable disorders of connective tissue

A skin biopsy contains the macromolecules present in most connective tissues: collagens, elastin, glycoproteins, and proteoglycans. The specific combination and assembly of these matrix components and their interactions with other structures (e.g., epidermal appendages, nerve and vascular networks) and cells are responsible for the distinction among specific regions of the dermis. The matrix components are interactive and interdependent and modification of one of them, by extrinsic (environmental) and/or intrinsic (systemic, genetic, age-related) factors, may have consequences on the tissue as a whole. The skin, therefore, provides a window through which it is possible to examine how mutations in one connective tissue macromolecule can change the interactions among matrix components and affect tissue structure and organization. Light and electron microscopic studies of skin from patients with inherited connective tissue disorders (e.g., Ehlers-Danlos syndrome, osteogenesis imperfecta, Marfan syndrome, cutis laxa) have led us to the following generalizations about what components change, how individual collagen or elastic fibers are altered and how individual alterations affect overall dermal organization: 1) There is a limited change in the repertoire of collagen fibrils in the skin; 2) there appears to be a greater range of abnormal structure in dermal elastic fibers than in the collagen fibrils; 3) the morphology of the fibroblastic cells may provide clues to the defect in matrix components; 4) similar structural abnormalities result from different molecular defect; 5) a molecular defect in one connective tissue molecule has consequences for the structural properties of other connective tissue components; and 6) although structural alterations in connective tissue fibers are rarely specific for a given disease, there are characteristic patterns of structural change in the matrix that may be used to confirm a diagnosis. These generalizations show that mutations rarely affect only a single aspect of macromolecular function and because of the interactions of matrix components in this complex organ (skin) often disturb the organization of the entire dermis. Genotype-phenotype relationships are important to understand if effective therapies are to be designed. The structure of skin should provide the next level of integration in our efforts to determine how mutations produce disease.     

Combined staining of elastic and collagen fibers for histopathological and differential diagnosis in aorta pathologies

Histochemical techniques are important for diagnosis of connective tissue fibers involved in different aorta pathologies. The aim of this study was to develop a histochemical staining method that identifies both elastic and collagen fibers simultaneously in the same section of aortic wall. Fragments of aorta from deceased dogs were processed according to standard histological technique for paraffin embedding. Sections were stained with orcein with counterstained with either light green or single step Gomori trichrome, and also orcein stain and picro-sirius red. Orcein stain combined with picro-sirius red allowed visualization of both elastic fibers (brown) and collagen fibers (red) with light microscopy using bright field illumination. Moreover, under polarized light microscopy only collagen fibers were detected, appearing as reddish birefringent fibers, confirming that picro-sirius red-stained fibers were collagen fibers. The combination staining by orcein and picro-sirius solutions provided visualization of both collagen and elastic fibers in the same section, facilitating identification of these connective tissue fibers in the aortic wall.     

Studies in Rheumatic Fever: VI. Ultrastructure of Chronic Rheumatic Heart Disease

The fine structure alterations in the atrium and atrial appendage, mitral valve and papillary muscle are described in 11 matched patients with chronic rheumatic heart disease. The muscle changes consisted of loss of myofilaments and accumulation of lipid and osmiophilic dense bodies. The connective tissue stroma of the atrium and the mitral valve showed extensive deposition of collagen and elastic fibers. There were numerous foci of collagen degeneration, characterized by fraying of the collagen fibers and accumulation of homogeneous granular material at these sites. Although the muscle changes were more striking, the connective tissue alterations appear important in the evolution of the chronic disease. The extent of collagen degeneration appeared to parallel the degree of collagen formation. The muscle fiber degeneration and connective tissue alterations did not correlate with the clinical findings. At the resolution of the electron microscope, the continuing process in the rheumatic heart appears to be primarily collagen formation and degradation rather than primary degeneration of the muscle fibers. It is the balance of these processes which determine the clinical state of the patient. Acute muscle damage along with evidence of inflammation do not seem to be associated with progressive, chronic rheumatic heart disease.     

Effect of formalin fixation on the ultrastructure of connective tissue components

Electron microscopic examinations of fibrillar components and the ground substance of human skin derma fixed in formaldehyde showed good preservation of the fibrillar structures. The typical changes in fixed collagen fibrils in negative staining include the lack of transversal lines in the zone A and poor manifestation of microfibrillarity in the zone B. Alterations in the ground substance are more significant. Staining with rutenium red reveals no reticular structure here, but floccular formations appear in the amorphous interfibrillar substance. Other species of rutenium-positive structures (sheaths of elastic fibers and collagen fibrils as well as lines of thin cross-striation of the latter) are well preserved. All these alterations should be taken into consideration in ultramicroscopical examinations of formalin-fixed connective tissue.     

The deep fascia and retinacula of the equine forelimb – structure and innervation

Recent advances in human fascia research have shed new light on the role of the fascial network in movement perception and coordination, transmission of muscle force, and integrative function in body biomechanics. Evolutionary adaptations of equine musculoskeletal apparatus that assure effective terrestrial locomotion are employed in equestrianism, resulting in the wide variety of movements in performing horses, from sophisticated dressage to jumping and high‐speed racing. The high importance of horse motion efficiency in the present‐day equine industry indicates the significance of scientific knowledge of the structure and physiology of equine fasciae. In this study, we investigated the structure and innervation of the deep fascia of the equine forelimb by means of anatomical dissection, histology and immunohistochemistry. Macroscopically, the deep fascia appears as a dense, glossy and whitish lamina of connective tissue continuous with its fibrous reinforcements represented by extensor and flexor retinacula. According to the results of our histological examination, the general structure of the equine forelimb fascia corresponds to the characteristics of the human deep fasciae of the limbs. Although we did find specific features in all sample types, the general composition of all examined fascial tissues follows roughly the same scheme. It is composed of dense, closely packed collagen fibers organized in layers of thick fibrous bundles with sparse elastic fibers. This compact tissue is covered from both internal and external sides by loosely woven laminae of areolar connective tissue where elastic fibers are mixed with collagen. Numerous blood vessels running within the loose connective tissue contribute to the formation of regular vascular network throughout the compact layer of the deep fascia and retinacula. We found nerve fibers of different calibers in all samples analyzed. The fibers are numerous in the areolar connective tissue and near the blood vessels but scarce in the compact layers of collagen. We did not observe any Ruffini, Pacini or Golgi‐Mazzoni corpuscles. In conclusion, the multilayered composition of compact bundles of collagen, sparse elastic fibers in the deep fascia and continuous transition into retinacula probably facilitate resistance to gravitational forces and volume changes during muscle contraction as well as transmission of muscle force during movement. However, further research focused on innervation is needed to clarify whether the deep fascia of the equine forelimb plays a role in proprioception and movement coordination.     

Stereo architecture of the lamina propria in the mouse laryngopharynx in scanning electron microscopy.

In the ventral wall of the mouse laryngopharynx, a fairly large number of the epithelial papillae containing taste bud (provisionally denominated the pharyngeal papillae) were observed. The NaOH cellmaceration method was applied in order to demonstrate the stereo architecture of the connective tissue papillae (CTP) of the pharyngeal papillae. The CTP appeared as a cylindrical wall surrounding a round depression, and consisted of a delicate meshwork of collagen fibrils. It is suggested that the CTP constitute the skeletal framework of the pharyngeal papillae and that the round depression corresponds to the site of taste bud. Furthermore, the collagen fibrillar architecture in the extrapapillary region appeared to be arranged to meet specific functional needs. That is, in the rostral end of the laryngopharynx, the collagen fibrils ran solitarily to form a coarse meshwork and seemed to allow the epithelium a certain degree of freedom of motion in swallowing. On the other hand, in the caudal part the fibrils concentrated into the thick bundles of the fibers running side by side along the long axis of the laryngopharynx and, therefore, appeared to play an important role in resisting the excessive stretching force.