Morphometric study of human alveolar ducts based on serial sections

Interactive computerized morphometry was used for the quantitative study of the terminal airway branches (alveolar ducts) that followed the last bronchioles in three human acini. Two normal adult human lungs from the autopsy service were fixed by instillation and serial sections were prepared; three tissues blocks showing a central bronchiole were selected. Primary and secondary alveolar walls were traced and the following parameters were measured: volume, surface area (of primary and secondary septa), curvature (in equivalent radius) for branches of individual generations, and cumulative values starting with the first alveolar duct and moving peripherally. Although branching was dichotomous, we noticed considerable asymmetry in the pattern of branching and number of side branches. The branching trees of alveolar ducts that we studied comprised 6,7, and 10 generations. The average volume of ducts was 0.04-0.13 mm3, the surface area of primary walls ranged from 0.3616 to 0.7931 mm2 and of secondary septal walls from 0.0100 to 0.0647 mm2. The equivalent radius of curvature was between 22.7 and 38.1 microns. Cumulative increases of volume and surface area revealed similarity in the first five generations. Secondary walls represented only 4% (or 8% if 2 sides are considered) of the primary surface area, strengthening the view that alveoli are incompletely developed side chambers secondary to the alveolar ducts.     

Structural aspects of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] tuberculate ectomycorrhizae

Summary Tubercles of Pseudotsuga menziesii consisted of clusters of ectomycorrhizae surrounded by a peridiumlike rind. Energy dispersive spectroscopy demonstrated that crystals found in the zone of loose hyphae extending from the inner rind to the mantle of each root probably contain calcium oxalate. Inner mantle and Hartig net hyphae showed a labyrinthine branching pattern and stored carbohydrates and protein. The Hartig net formed up to inner cortical cells which had thickened, darkly stained walls. Bacteria were located either along with hyphae within the rind or as colonies on the surface of the tubercle.     

Further considerations in a theoretical description of gas transport in lung airways

A discrete one-dimensional model of convection-diffusion in branching alveolar ducts is described and it is shown that, for a suitable choice of effective axial dispersion, the solution closely approximates that for an axially symmetric representation, at least for Peclet numbers Pe<1. Following earlier work a composite model of a uniform lung is formed by matching such a respiratory pathway (now having the more convenient one-dimensional form) onto a trumpet representation of the conducting airways. Enhanced mixing due to heart action, and isotropic volume changes of trumpet (in addition to the pathway) during breathing are additional factors included. Calculations are made of O₂ concentrations during steady-state breathing and of the concentration of inert gas during single breath wash-out of a gas mixture containing it. Predicted alveolar levels in each case agree extremely well with published data, although no alveolar slope is obtained for the inert gas.     

A model of the lung structure and its validation

As a framework to describe the structure of the lung, a theory is presented under the assumptions that all alveoli are initially equal and space filling, are ventilated as uniformly as possible, and obey the laws of elasticity. A combination of the tetrakaidecahedron (14-hedron) and the order-2 14-hedron formed by 14 14-hedra surrounding a central one that is perforated for ventilation meets the requirements. Alveolar ductal tree is formed by these order-2 polyhedra. Equilibrium and elasticity require the alveolar mouths to be curved and convex toward the alveolar wall. Perforation of additional walls causes a variety of alveolar shapes. The predicted shapes of the alveoli, the shapes of alveolar mouths, the lengths of sacs and ducts, the statistics of the dihedral angles, stars, corners, lines, dots, and vertices compare well with available morphometric data. The vascular and bronchial trees are joined at the alveolar level: each arteriole supplies 0.75 and each venule drains 0.72 order-2 polyhedra.     

Morphology of the airways and lung parenchyma in hatchlings of the loggerhead sea turtle,Caretta caretta

Light microscopy as well as scanning and transmission electron microscopy revealed the lungs of loggerhead sea turtle (Caretta caretta), hatchlings to be multichambered with several separate open chambers communicating with a cartilage-reinforced central intrapulmonary bronchus. This central bronchus is structurally analogous to an oversized mammalian respiratory bronchiole. The subsequent branching airways, chambers and niches, are in many ways structurally and functionally similar to mammalian alveolar ducts and alveolar sacs, respectively. The airways are lined by a pseudostratified, columnar epithelium comprised of ciliated, nonciliated secretory, and basal cells. Histochemically, the epithelium is found to contain cells secreting both sialomucins and sulfomucins, as well as a neutral serous secretion. Small granule cells, a type of neuroendocrine cell similar to those seen in mammals, are scattered among the other airway cells. The gas-exchange areas, termed ediculae, are lined by the respiratory type I and type II pneumocytes, as in mammals. Abundant smooth muscle is seen in the trabeculae and interedicular septa of the lung tissue. © 1996 Wiley-Liss, Inc.     

扁桃花药开裂前后壁层细胞形态变化及分析

为探明扁桃花药开裂前后壁层细胞形态变化,以鹰咀扁桃鳞片开裂期、小蕾期、大蕾期和盛花期的花蕾为研究材料,运用石蜡切片法结合铁苏木精染色法、考马斯亮蓝染色法、PAS染色法对花药壁层细胞进行染色;同时用Nikon SMZ-250体视显微镜拍摄花药开裂过程,观测花粉粒长、短轴长度。结果表明:(1)从鳞片开裂期到小蕾期,花粉粒的长、短轴长度都增大,多糖颗粒数量增多,绒毡层细胞完全消失,中层细胞和药隔处细胞逐渐溶解;药室内壁细胞切向长度增加幅度大于径向长度,内、外壁长度都增大,螺旋状纤维进一步形成;表皮细胞切向长度增加幅度大于径向长度。(2)从小蕾期到大蕾期花粉粒长、短轴长度明显增大,多糖颗粒持续增多;中层细胞和药隔处细胞大部分溶解;药室内壁细胞径向、切向长度持续增大,内壁长度增大、外壁长度趋于稳定,多糖颗粒数量减少,螺旋状纤维基本形成;表皮细胞切向减小幅度大于径向。(3)从大蕾期到花药半开裂,花粉粒长、短轴长度稍微增大;中层细胞和药隔处细胞完全溶解;药室内壁细胞切向长度持续增大,径向长度趋于稳定,内壁长度持续增大,外壁长度逐渐减小,多糖颗粒数量较少;表皮细胞切向、径向长度持续减小。(4)花药半开裂后,花粉粒长、短轴长度都减小;药室内壁细胞和表皮细胞切向、径向长度都减小;药室内壁细胞内、外壁长度减小并趋于接近,内壁长度减小趋势出现晚于外壁。研究认为,扁桃花药壁层细胞形态变化是花药开裂的基础,并与花药开裂密切相关。     

Branching pattern of airways and air spaces of a single human terminal bronchiole.

A polyurethane-foam enlarged reconstruction was made from serial sections of a portion of young adult human lung parenchyman. Study of the progeny of a terminal bronchiole disclosed three generations of respiratory bronchioles and an irregular branching pattern of eight generations of alveolar ducts. Sacs and alveoli arose from the lateral and distal aspects of all generations of ducts. There were an average of 3.5 alveoli per sac. Considering the terminal bronchiole as the first generation branch of the acinus, over 60 per cent of the alveoli counted and predicted were members of the 10-12th generations. The acinus contained one terminal bronchiole and approximately 14 respiratory bronchioles, 1,200-1,500 ducts, 2,500-4,500 sacs, and 14,000-20,000 alveoli.     

Transport of O2 along a model pathway through the respiratory region of the lung

A pathway through the system of branching in the respiratory region of the lung is modelled by a circular cylinder, closed at one end, with partitions which define the component respiratory units. In this model the transport of O₂ during inspiration, generated by diffusion is compared with that produced by diffusion together with convection and the importance of convection in the respiratory region in promoting oxygen uptake at the alveolar wall is discussed. For this discussion it is only necessary to consider inspiration. The equations are solved numerically for flow rates of 10, 85 and 200 liters/min. O₂ uptake at the wall and curves of constant O₂ concentration are shown to illustrate the influence of convection. It is found that after a 2 sec inspiration from an O₂ tension of 98 mm Hg and a lung volume of 2300 ml, convection is about 12 per cent as important as diffusion at a flow rate of 85 liters/min, whereas at 10 liters/min convection is only about 0.4 per cent as important as diffusion.     

Morphology and histology of the swimbladder and infrastructure of respiratory epithelium in the air-breathing catfish, Pangasius sutchi (Pangasiidae)

The swimbladder of Pangasius sutchi is made up of fibrosa, collagenic fibre walls and mucosa; its walls extend into the lumen to form dense respiratory alveoli, with the inner surface covered by a highly vascularized respiratory epithelium. The thin epithelial cells have the structural characteristics and function of type I and type II cells of lung alveoli in higher mammals. These cells and the endothelial cells compose the barrier through which gases must pass in the exchange between blood and air. The study shows that the swimbladder of P. sutchi is an important accessory respiratory organ.     

Extracellular hydrogen peroxide,produced through a respiratory burst oxidase/superoxide dismutase pathway,directs ingrowth wall formation in epidermal transfer cells of Vicia faba cotyledons

The intricate, and often polarized, ingrowth walls of transfer cells (TCs) amplify their plasma membrane surface areas to confer a transport function of supporting high rates of nutrient exchange across apo-/symplasmic interfaces. The TC ingrowth wall comprises a uniform wall layer on which wall ingrowths are deposited. Signals and signal cascades inducing trans-differentiation events leading to formation of TC ingrowth walls are poorly understood. Vicia faba cotyledons offer a robust experimental model to examine TC induction as, when placed into culture, their adaxial epidermal cells rapidly (h) and synchronously form polarized ingrowth walls accessible for experimental observations. Using this model, we recently reported findings consistent with extracellular hydrogen peroxide, produced through a respiratory burst oxidase homolog/superoxide dismutase pathway, initiating cell wall biosynthetic activity and providing directional information guiding deposition of the polarized uniform wall. Our conclusions rested on observations derived from pharmacological manipulations of hydrogen peroxide production and correlative gene expression data sets. A series of additional studies were undertaken, the results of which verify that extracellular hydrogen peroxide contributes to regulating ingrowth wall formation and is generated by a respiratory burst oxidase homolog/superoxide dismutase pathway.     

The respiratory system of the genusCallithrix,the South American monkey

It has been described the cytology of the following parts of the respiratory system of some South American primates:Callithrix jacchus andCallithrix argentata melanura. The nasal cavities are divided into three parts: a vestibule, covered with a stratified nonkeratinized squamous epithelium; the respiratory portion, consisting of a pseudostratified columnar ciliated epithelium with goblet cells and the olfactory portion which is also covered with a high respiratory epithelium without goblet cells. The trachea is lined with a mucous membrane, whose epithelium is pseudostratified columnar ciliated with scarce goblet cells in the proximal portion unlike to the distal one. In the dorsal portion of the trachea, at the level of the gap between the two ends of incomplete cartilaginous rings, the epithelial lining is of transitional type. The incomplete hyaline cartilaginous rings present centers of calcification. The right and left lungs consist of two and three lobes respectively characteristic for these species, but they are not divided into lobules by connective tissue as in other ones. The bronchi, bronchioles and the respiratory portion, respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli present the typical respiratory structure with exception of their cartilaginous configuration; the cartilage continues as far as the respiratory bronchioles and alveolar ducts. These last structures are formed by a thin squamous epithelium, in which we observed two types of alveolar lining cells. This work was supported by grants from the Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET) and EHIGE program. Postgraduated fellow from CONICET. established Investigator and Director of EHIGE (Estudio Histológico comparado del Sistema de Glándulas Endócrinas) from CONICET.     

Monoclonal antibody identification of a type II alveolar epithelial cell antigen and expression of the antigen during lung development

A monoclonal antibody identifying an antigen expressed by rat type II alveolar epithelial cells, but not by type I epithelial cells or other mature lung cells, was produced by immunization of mice with cells of the rat L2 cell line. The antigen recognized by the antibody was present on the microvillous luminal surface of type II epithelial cells. In adult rat lung, only type II epithelial cells bound the antibody. During fetal development the antigen was expressed by cuboidal epithelial cells lining the respiratory ducts of the first divisions of the tracheal bud, but not by epithelial cells lining the esophagus or trachea. The antigen continued to be expressed by cuboidal epithelial cells lining the larger respiratory ducts until approximately 19 days gestational age. Thereafter, expression was increasingly limited to selected single cells or clusters of two to four cuboidal cells in the smallest ducts. By the 21st postnatal day, the antigen was expressed only by type II alveolar epithelial cells. Type II alveolar epithelial cells isolated from adult lung and the L2 cell line in culture expressed the antigen on the cell surface. A protein of approximately 146,000 Mr was isolated by immunoadsorption of the antigen from non-ionic detergent extracts of type II cells and L2 cells. Preliminary studies of the binding of the antibody to other rat tissues indicate that the antibody binds to renal proximal tubular epithelial cells of the kidney and the luminal surface of the small bowel epithelial cells.     

Airway level at which edema liquid enters the air space of isolated dog lungs

To identify lung units associated with liquid leakage into the air space in high-pressure pulmonary edema, we perfused air-inflated dog lung lobes with albumin solution to fill the loose peribronchovascular interstitium. Next, we perfused the lobes for 90 s with fluorescent albumin solution then froze the lobes in liquid nitrogen. This procedure confined the fluorescent perfusate to the liquid flux pathway between the circulation and the air space and eliminated the previously filled peribronchovascular cuffs as a source of the fluorescence that entered the air space. We divided each frozen lobe into three horizontal layers and prepared fluorescence-microscopic sections of each layer. In the most apical layers where alveolar flooding was minimal, 10.6 +/- 21.0% (SD) of alveolar ducts were either fluorescence filled or air filled and continuous with fluorescence-filled alveoli. In the same layers, 11.0 +/- 19.0% of respiratory bronchioles were similarly labeled. No terminal bronchioles in these layers were fluorescence labeled. This suggested that the fluorescent albumin entered the air space across the epithelium of respiratory bronchioles, alveolar ducts, or their associated alveoli. To simulate an alternative explanation, i.e., that fluorescence first entered central airways then flowed into peripheral air spaces, we prepared two additional lobes that we first partially inflated with fluorescent albumin then filled to capacity with air. This pushed the fluorescent solution along the airways into the lung periphery. In these lobes the ciliary lining of bronchi and terminal bronchioles was fluorescence coated. By comparison, cilia in fluorescence-perfused lobes were not coated. We conclude that alveolar flooding in hydrostatic pulmonary edema occurs across the epithelium of alveolar ducts, respiratory bronchioles, or their associated alveoli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Determining deposition sites of inhaled lung particles and their effect on clearance

An essential component of lung defense is clearance of particulates and infectious vectors from the mucus membrane of the tracheobronchial tree and the alveolar regions of the lung. To partition clearance between these areas we determined the bronchial branching pattern, the anatomical sites of particle deposition, and subsequent clearance in the same animal. Using a 2.85-microns particle tagged with 57Co for inhalation and deposition in the sheep lung, we followed clearance via a series of computer-stored gamma-scintillation lung images. The same sheep was reinhaled, and the particle distributions for both inhalations were compared. After the animals were killed, the bronchial branching pattern and length of the bronchial tree were documented. The number of particles depositing in all bronchi down to 1 mm diam was determined by scintillation counting, and the number in respiratory bronchioles and alveoli was microscopically counted. We conclude that particles deposited in bronchi greater than or equal to 1 mm diam clear in 2-4 h postdeposition. Bronchi distal to 1-mm-diam bronchi and alveoli clear evenly over 72 h, and the number of particles equal to the tracheobronchial deposition cleared after 45 h.     

Binding of adenovirus capsid to dipalmitoyl phosphatidylcholine provides a novel pathway for virus entry

Adenovirus (Ad) is an airborne, nonenveloped virus infecting respiratory epithelium. To study the mechanism of Ad entry, we used alveolar adenocarcinoma A549 cells, which have retained the ability of alveolar epithelial type II cells to synthesize the major component of pulmonary surfactant, disaturated phosphatidylcholine. Stimulation of phosphatidylcholine secretion by calcium ionophore or phorbol ester augmented the susceptibility of these cells to Ad. Both Ad infection and recombinant-Ad-mediated transfection increased in the presence of dipalmitoyl phosphatidylcholine (DPPC) liposomes in culture medium. Importantly, in the presence of DPPC liposomes, virus penetrates the cells independently of virus-specific protein receptors. DPPC vesicles bind Ad and are efficiently incorporated by A549 lung cells, serving as a virus vehicle during Ad penetration. To identify the viral protein(s) mediating Ad binding, a flotation of liposomes preincubated with structural viral proteins was employed, showing that the only Ad protein bound to DPPC vesicles was a hexon. The hexon preserved its phospholipid-binding properties upon purification, confirming its involvement in virus binding to the phospholipid. Given that disaturated phosphatidylcholine not only covers the inner surface of alveoli in the lungs but also reenters alveolar epithelium during lung surfactant turnover, Ad binding to this phospholipid may provide a pathway for virus entry into alveolar epithelium in vivo.     

A strain energy function for lung parenchyma

The strain energy for the air-filled lung is calculated from a model of the parenchymal microstructure. The energy is the sum of the surface energy and the elastic energies of two tissue components. The first of these is the peripheral tissue system that provides the recoil pressure of the saline-filled lung, and the second is the system of line elements that form the free edges of the alveolar walls bordering the alveolar ducts. The computed strain energy is consistent with the observed linear elastic behavior of parenchyma and the data on large deformations around blood vessels.     

The nasopalatine ducts and associated structures in the rhesus monkey (Macaca mulatta): topography, prenatal development, function, and phylogeny

Morphological and developmental characteristics of the rhesus monkey nasopalatine duct system and associated primary palatal structures are described along with functional and phylogenetic considerations. Examination of five adult palates and coronal sections of 13 fetal palates together with dissections of a sixth adult specimen and of a 119-day-old fetal palate reveal that the lateral lobes of the tripartate incisive papilla cover clefts leading into the ducts. The ducts pierce the bony palate to enter the nasal fossae in proximity to the incisive suture. The ontogenetic stability of the duct path reflects the retention of ancient duct and primitive choanae relationships and functionally maintains an optimal oral odorant-to-receptor channel. Sixteen timed pregnancy specimens (35-100 days) provided histological material for documenting rostral nasopalatal development. Duct primordia, identified at 35 days, had by 40 days formed the medial duct walls (conjoined septum-papilla from the primary medial palatal component), the lateral duct walls (maxillary processes), and the rostral walls (fused maxillary-intermaxillary components). The caudal walls derive from the fusion of palatal shelves with the papilla (45 days), thus distinguishing primary and secondary fusion modes. Duct epithelial maturation occurs between 70 and 100 days. The absence of a vomeronasal system is attributed to reduction of olfaction in reproductive behavior, while the presence of the coevolved nasopalatine ducts is linked to the persistence of epiglottal-velar valving. The ducts serve as oral food-odor conduits in otherwise functionally separated respiratory and digestive tracts.     

Ultrastructural studies of the zygote and oocyst wall formation of Eimeria truncata of the lesser snow goose

Zygote development and oocyst wall formation of Eimeria truncata occurred in epithelial cells in renal tubules and ducts of experimentally infected lesser snow geese (Anser c. caerulescens). Post-fertilization stages were present throughout the kidneys beginning nine days post-inoculation. Initially, a single plasmalemma enclosed the zygote, and type 1 wall-forming bodies (WF1) became labyrinthine and moved toward the surface. There, WF1 degranulated and formed the outer layer of the oocyst wall between the plasmalemma and a newly formed second subpellicular membrane. Several WF2 fused and formed the inner layer of the oocyst wall between the third and fourth subpellicular membranes. Six subpellicular membranes were observed during wall formation. Other features of oocyst development were similar to those of other eimerian species.     

Morphology of the terminal bronchiolar region of common laboratory mammals

The histomorphology of the terminal bronchiolar region of the mouse, rat, hamster, guinea pig, gerbil and rabbit was studied. Although some general structural similarities existed in the progressive intrapulmonary branching pattern of the airway tree between species, there were conflicting accounts in the literature about the presence of the respiratory bronchioles in common laboratory mammals. In our light microscopy study we failed to detect the existence of typical respiratory bronchioles with characteristic interruptions on their walls projecting into the alveoli. Frequently in these species the terminal bronchioles were short and abrupt, opening directly into several alveolar ductules.