Transmission electron microscopy of the epithelium of distal airways and pulmonary parenchyma of the goat lung

Vocal fold epithelial barrier in health and injury: a research review

PURPOSE

Vocal fold epithelium is composed of layers of individual epithelial cells joined by junctional complexes constituting a unique interface with the external environment. This barrier provides structural stability to the vocal folds and protects underlying connective tissue from injury while being nearly continuously exposed to potentially hazardous insults, including environmental or systemic-based irritants such as pollutants and reflux, surgical procedures, and vibratory trauma. Small disruptions in the epithelial barrier may have a large impact on susceptibility to injury and overall vocal health. The purpose of this article is to provide a broad-based review of current knowledge of the vocal fold epithelial barrier.

METHOD

A comprehensive review of the literature was conducted. Details of the structure of the vocal fold epithelial barrier are presented and evaluated in the context of function in injury and pathology. The importance of the epithelial-associated vocal fold mucus barrier is also introduced.

RESULTS/CONCLUSIONS

Information presented in this review is valuable for clinicians and researchers as it highlights the importance of this understudied portion of the vocal folds to overall vocal health and disease. Prevention and treatment of injury to the epithelial barrier is a significant area awaiting further investigation.

Morphological analysis of the lung of neonatal yak

Although yaks play an important role as companion or pack and draught animals on Chinese plateaus in alpine and sub-alpine regions, morphological studies and anatomical data on the lung of yak are sparse. To provide anatomical descriptions and morphometric data, 10 one-day-old yaks were examined by means of dissection, light and electron microscopy. The measurements of lung were made on dissected specimens and histological sections. Unequal dichotomous branching was demonstrated in the dissected tracheobronchial tree. The diameters of bronchial airways and height of epithelium were measured, and showed that the variation of diameters in airways was always greater than that of height of epithelium. In addition, the thickness of muscularis, cartilage and adventitia was examined, as well as the number of goblet and Clara cells in airways. Ultrastructural studies showed that the surface epithelium was mainly composed of goblet, ciliated, Clara and basal cells, similar to that in other domestic animals. Under electron microscope, two distinctive types of ciliated cells could be seen in the tracheobronchial epithelium. The first type contained some mitochondria, distended smooth endoplasmic reticulum (SER), little rough endoplasmic reticulum (RER) and numerous vacuoles in electron-lucent cytoplasm. The second type had dense cytoplasm with abundant mitochondria, RER and no vacuoles. Both types were rich of glycogen granules. The goblet cells in neonatal yak lung had the following characteristic features: dentate nucleus in dense cytoplasm, with stacks of RER and numerous dense membrane-bounded mucous droplets, which were round or oval, often with an electron-lucent core. The droplets were not confluent. Glycogen granules were numerous, and Golgi complex was occasionally present. Clara cells were dome-shaped and usually protruded into the airway lumen. Large amounts of SER and many secretory droplets were found within the cytoplasm. Several typical 'clefts' were also found in the cytoplasm.

Occurence of lipid bodies in canine type II pneumocytes during hypothermic lung ischemia

Type II pneumocytes defend the pulmonary alveolus by synthesis and secretion of surfactant and by contributing to alveolar epithelial regeneration. Lipid bodies are regarded as intracellular domains for the synthesis of eicosanoid mediators that can be induced by inflammatory stimuli. The aim of the present study was to establish whether hypothermic ischemic lung storage without further preservation measures leads to an induction of lipid body formation in canine type II pneumocytes. The lungs of 18 dogs were fixed for transmission electron microscopy (TEM) immediately after cardiac arrest (six double lungs) and after ischemic storage in Tutofusin solution at 4 degrees C for 20 min, 4 hr, 8 hr, and 12 hr (six single lungs, respectively). Type II pneumocytes were analyzed qualitatively by conventional TEM (CTEM) and quantitatively by stereology. The relative phosphorus content of surfactant containing lamellar bodies, lipid bodies, and intermediate forms was investigated by energy-filtering TEM (EFTEM). By CTEM, lipid bodies as well as forms intermediate between lipid bodies and lamellar bodies were already noted in the control group but were more pronounced in the ischemia groups. Beginning at 20 min of ischemic storage, a significant increase in the volume density of lipid bodies was noted in the ischemic groups as compared to the control group. By EFTEM, the highest intracellular phosphorus signals were recorded over lamellar bodies and lamellar areas of intermediate forms in all experimental groups, while lipid bodies and homogeneous areas of intermediate forms did not show a clear phosphorus signal. These results indicate that the formation of lipid bodies in canine type II pneumocytes is induced early during ischemic lung storage.

Successful induction of ovine pulmonary adenocarcinoma in lambs of different ages and detection of viraemia during the preclinical period

Ovine pulmonary adenocarcinoma (OPA) can be reproduced consistently in neonatal lambs by intratracheal injection of inocula containing jaagsiekte sheep retrovirus (JSRV). In this study, clinical disease, confirmed pathologically as OPA, was induced in a high proportion of lambs that had been inoculated intratracheally with infectious lung fluid at 1, 3 and 6 months of age. The incubation periods, however, were longer in these three age groups than in 1-week-old lambs that were used as controls. Viraemia was detected in all age groups before onset of clinical signs, but occurred later in older animals. These results suggest an age-dependent susceptibility to OPA that could be determined by the availability of JSRV target cells in the ovine lung. The feasibility of inducing OPA in older lambs and detecting JSRV viraemia in preclinical stages enables improved studies on the pathogenesis, assessment of vaccines, diagnosis and control of the disease.

Development of the lung of the brushtail possum, Trichosurus vulpecula

The developing lung of the brushtail possum, Trichosurus vulpecula, was studied by light microscopy, and transmission electron microscopy was used to study the morphology of the conducting airways in the adult. Bronchi did not extend beyond the hilus of each of the six lobes of the lung, and lobules were supplied by major bronchioles. By 105 days post partum, bronchi and bronchioles were fully formed, coinciding with the emergence of mucosal associated lymphoid tissue (MALT), which preceded alveolar maturation by approximately 20 days. In the adult lung, goblet cells were rarely observed in the mucosal epithelium of bronchi, whereas Clara cells were present in the mucosa of all airways, increasing proportionately as the conducting and respiratory portions narrowed distally. Although the airways of the possum lung have a poorly developed mucociliary blanket, this may be compensated for by the large numbers of Clara cells and adequate supply of MALT.

Estrogen-induced microvilli and microvillar channels and entrapment of surfactant-lipids by alveolar type I cells of bovine lung

The ATI cells are simple, flat squamous epithelial cells, which are evolved to function as a component of the alveolar-capillary membrane, ideally designed for gaseous exchange. They inherently lack an active metabolic machinery and lead a precarious existence in the face of hostile environment. On the other hand, the ATI cells of the lung of ruminating animals are endowed with structure-functional properties which enable them to exert a selective barrier function against a wide range of osmotic pressure gradients at their luminal surface. Such gradients are created by a complex gaseous homeostasis due to expectoration of several gases and volatile fatty acids originating from the complex stomach of the ruminants. The purpose of this study is to examine the effect of estradiol propionate on the ultrastructure of the ATI cells and their interaction with the surfactant lipids. The lungs of estrogen and dexamethasone treated male calves were harvested for electromicroscopic examination. The evidence is presented that estradiol induced the formation of microvilli and microvillar channels at the luminal surface. At these regional modifications, intense interactions with the surfactant lipids and their entrapment into the pathways of endocytosis, took place in the squamous part of the ATI cells. Concurrently, large basal protrusions ended up as long lamellipods deep into the alveolar interstitium. The filamentous cytoskeletal network and microtubules intermixed with the translocated organelles such as Golgi apparatus and associated coated and uncoated vesicles. The results of this study support the hypothesis that estrogen regulate the selective barrier-function of the ATI cells. The entrapment of surfactant lipids under the influence of estrogen by ATI cells is a significant change perhaps in response to extracellular stimuli and expression of transmembrane receptors. It implies that these epithelial cells are specially evolved to adapt to a complex gaseous homeostasis in the lung of the ruminating ungulates.

Basal secretion of lysozyme from human airways in vitro

The aim of this study was to examine the basal release of lysozyme from isolated human lung tissues. Measurements of lysozyme in the fluids derived from lung preparations were performed using a rate-of-lysis assay subsequent to acidification of the biological samples. Lysozyme released from bronchial preparations into fluids was greater than that observed for parenchymal tissues. The lysozyme quantities detected in bronchial fluids were not modified by removal of the surface epithelium. Furthermore, the quantities of lysozyme in bronchial fluids was correlated with the size of the bronchial preparations. These results suggest that the lysozyme was principally secreted by the human bronchi (submucosal layer) rather than by parenchyma tissues and that a greater release was observed in the proximal airways.