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.     

Pulmonary acinus: geometry and morphometry of the peripheral airway system in rat and rabbit

The geometry and morphometry of intraacinar airways in rat and rabbit lungs were studied from silicone rubber casts. Acini, defined as the complex of alveolated airways distal to the "terminal" bronchiole, were trimmed off the bronchial tree. In both species, the acinar volume followed a log-normal distribution over a range in size of one order of magnitude. At an inflation level of 60% total lung capacity, their mean volume was 1.86 mm3 in the rat and 3.46 mm3 in the rabbit. On a representative sample of acini of different volumes, the branching pattern was characterized as irregular dichotomy, and the segment length and inner and outer diameters were measured. The average acinus had a mean of six generations in the rat and seven in the rabbit. Both showed a decrease in segment length and inner diameter with each generation. The mean longitudinal pathway length--that is, the distance from the initial acinar segment to the terminal sacs--was found to depend on the cube root of the acinar volume in both species. It was calculated at 1.46 and 1.95 mm for rat and rabbit, respectively.     

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.     

Regenerative growth of respiratory bronchioles in dogs

Loss of lung units due to pneumonectomy stimulates growth of the remaining lung. It is generally believed that regenerative lung growth involves only alveoli but not airways, a dissociated response termed "dysanaptic growth." We examined the structural response of respiratory bronchioles in immature dogs raised to maturity after right pneumonectomy. In another group of adult dogs, we also examined the effect of preventing mediastinal shift after right pneumonectomy on the response of respiratory bronchioles. In immature dogs after pneumonectomy, the volume of the remaining lung increased twofold, with no change in volume density, numerical density, or mean diameter of respiratory bronchiole, compared with that in the control lung. The number of respiratory bronchiole segments and branch points increased proportionally with lung volume. In adult dogs after pneumonectomy, prevention of mediastinal shift reduced lung strain at a given airway pressure, but lung expansion and regenerative growth of respiratory bronchiole were not eliminated. We conclude that postpneumonectomy lung growth is associated with proliferation of intra-acinar airways. The proportional growth of acinar airways and alveoli should optimize gas exchange of the regenerated lung by enhancing gas conductance and mixing efficiency within the acinus.     

Smooth muscle development during postnatal growth of distal bronchioles in infant rhesus monkeys.

Development of smooth muscle in conducting airways begins early in fetal life. Whereas the pattern and regulation of smooth muscle differentiation are well-defined, the impact of airway growth on the process is not. To evaluate the transformations in organization during postnatal growth, smooth muscle bundle organization (size, abundance, and orientation) was mapped in five generations of distal airways of infant rhesus monkeys (5 days and 1, 2, 3, and 6 mo old). On the basis of direct measurement of the bronchiole proximal to the terminal bronchiole, length increased by 2-fold, diameter by 1.35-fold, and surface area by 2.8-fold between 5 days and 6 mo of age. Smooth muscle bundle size was greater in proximal bronchioles than in respiratory bronchioles and did not change with age. However, relative bundle size decreased in proportion to airway size as the airways grew. Relative bundle abundance was constant regardless of airway generation or age. The distribution of smooth muscle bundle orientation changed with age in each airway generation, and there were significant changes in the terminal and respiratory bronchioles. We conclude that smooth muscle undergoes marked organizational changes as airways grow during postnatal development.     

Temporal and spatial distribution of ciliogenesis in the tracheobronchial airways of mice

Little is known about ciliogenesis as it proceeds through the entire airway tree, from the trachea to the terminal bronchioles, especially during the postnatal period. The purpose of this study was to define the spatial and temporal (prenatal and postnatal) pattern of normal cilia development in the mouse. Three airway generations representing the entire airway tree were examined: trachea, lobar bronchi, and terminal bronchiole. Ciliated cells in lung lobe whole mounts were labeled with a fluorescent dye for confocal microscopy, and ciliated cell surface density was measured for each airway generation and age. The same samples were examined by scanning electron microscopy to verify the appearance of ciliated cells among the differentiating epithelium of the airways. Ciliated cells were first detected in the trachea and lobar bronchi at 16 days gestational age (DGA) and in the terminal bronchioles at 18 DGA. Ciliated cell surface density increased with prenatal and postnatal age at all airway levels. However, the ciliated cell surface density of the trachea and lobar bronchi was always greater compared with the terminal bronchiole. In conclusion, the study revealed that in developing tracheobronchial airways of the mouse: 1) Ciliogenesis differs temporally and spatially by airway generation; 2) Ciliated cell surface density increases with age in all airway generations, but density decreases in a proximal to distal direction; and 3) A significant portion of ciliogenesis continues after birth. This study provides a healthy basis for investigations of neonatal pulmonary disease or pollutant toxicity affecting cilia and its functions.     

一种室内饲养麦蚜的方法

介绍利用水培麦苗大量饲养麦蚜的技术。在不补充营养液的条件下麦苗可以维持10~15d,一般在饲养条件下可以1周换1次麦苗。小麦种子在经过24h浸种后,平铺在底部垫有滤纸的直径9cm的培养皿中,在25℃,4d后就可以接种麦蚜。适宜的试样条件为温度在18~25℃,相对湿度50%~70%,光周期为17hr∶7hr,饲养1代大约需要5~9d时间,每皿可养麦蚜500头以上。经过40代以上的连续饲养,蚜虫体重和每蚜产幼蚜数量没有明显降低趋势。     

Evidence for minimal oxygen heterogeneity in the healthy human pulmonary acinus

It has been suggested that the human pulmonary acinus operates at submaximal efficiency at rest due to substantial spatial heterogeneity in the oxygen partial pressure (Po(2)) in alveolar air within the acinus. Indirect measurements of alveolar air Po(2) could theoretically mask significant heterogeneity if intra-acinar perfusion is well matched to Po(2). To investigate the extent of intra-acinar heterogeneity, we developed a computational model with anatomically based structure and biophysically based equations for gas exchange. This model yields a quantitative prediction of the intra-acinar O(2) distribution that cannot be measured directly. Temporal and spatial variations in Po(2) in the intra-acinar air and blood are predicted with the model. The model, representative of a single average acinus, has an asymmetric multibranching respiratory airways geometry coupled to a symmetric branching conducting airways geometry. Advective and diffusive O(2) transport through the airways and gas exchange into the capillary blood are incorporated. The gas exchange component of the model includes diffusion across the alveolar air-blood membrane and O(2)-hemoglobin binding. Contrary to previous modeling studies, simulations show that the acinus functions extremely effectively at rest, with only a small degree of intra-acinar Po(2) heterogeneity. All regions of the model acinus, including the peripheral generations, maintain a Po(2) >100 mmHg. Heterogeneity increases slightly when the acinus is stressed by exercise. However, even during exercise the acinus retains a reasonably homogeneous gas phase.     

A three-dimensional model of the human pulmonary acinus.

A three-dimensional (3-D) model of the human pulmonary acinus, a gas exchange unit, is constructed with a labyrinthine algorithm generating branching ducts that fill a given space completely. Branching down to the third respiratory bronchioles is generated with the proposed algorithm. A subacinus, a region supplied by the last respiratory bronchiole, is approximated to be a set of cubic cells with a side dimension of 0.5 mm. The labyrinthine algorithm is used to determine a pathway through all cells only once, except at branching points with the smallest path lengths. In choosing each step of a pathway, random variables are used. Resulting labyrinths have equal mean path lengths and equal surface areas of inner walls. An alveolus can be generated by attaching alveolar septa, 0.25 mm long and 0.1 mm wide, to the inner walls. Total alveolar surface area and numbers of alveolar ducts, alveolar sacs, and alveoli in our 3-D acinar model are in good accordance with those reported in the literature.     

Formation of cylindrical multicellular aggregate (cylindroid) and expression of liver specific functions of primary rat hepatocytes

In our studies of the development of a hybrid artificial liver, we investigated the formation of cylindrical multicellular aggregate (cylindroid) of primary rat hepatocytes on a pressed sheet of polyurethane foam (pressed–PUF) as a culture substratum. Hepatocytes formed cylindroids by attaching to a pressed–PUF surface, peeling off from the surface and aggregating. The diameter and length of most cylindroids were approximately 200–500 μm and 500 μm–2 mm, respectively. The activities of liver specific functions (albumin secretion and ammonia metabolism) of hepatocyte cylindroids were equivalent to or higher than those of hepatocyte spheroids. These results suggest that hepatocyte cylindroids can maintain highly differentiated functions longer than hepatocyte spheroids, and that a PUF/cylindroid culture may be effective to develop of a hybrid artificial liver. This revised version was published online in August 2006 with corrections to the Cover Date.     

Morphometric measurement of local curvature of the alveolar ducts in lung mechanics

We have performed partial serial reconstructions of an acinus of the rabbit lung and determined the apparent existence of numerous heterogeneities in length, diameter, and local curvature in individual generation branches of the lung. We believe that structural changes during respiratory movements may include changes in the length and diameter of the whole duct. Alveoli are seen to be side differentiations secondary to the ducts in the gas-exchanging parenchyma of the rabbit lung. We have developed a technique for measuring local curvature in simple reconstructed ducts from the average of the integral curvation of the section contour. The contour curvature is measured from the chain code representation of the sampled contour from digital image analysis. The stereological requirements of an unbiased and random selection of contours is approached here by the random orientation of the individual alveoli of a single duct. Over 700 sections through the last four airway generations (alveolar ducts) at 3-micron intervals were analyzed. The average integral curvature ranges from 7.7 to 9.5 (mean 8.9) mm-1 for sixth- and seventh-generation branches from the start with volumes for the segments from 0.022 to 1.198 (mean 0.497) mm3.     

Aspects of the population ecology of Lucinomaborealis (L.) (Bivalvia) in Raunefjorden,Western Norway

2194 Lucinoma borealis (L.) were obtained from 99 quantitative (0.2 m²) samples of substratum (stratified random sampling) collected between November 1975 and October 1976 in the archipelago of Eggholmane ≈20 km south of Bergen. The depth range of the 20900 m² area was 0.3–13.3 m, and the bottom sediment (fine to very coarse sand) was rich in calcium carbonate. The highest density was found in the deep (≈ 8–13 m) sub-areas, with fine sediment (median grain-size diameter ≈ 0.3–0.5 mm). L. borealis was the most abundant bivalve species in the area studied (59.6%, by number). The average density was 22.2 (C.I. ± 5.4) ind. · 0.2 m ^?2, and the biomass was 690 (C.I. ± 116) mg AFDW · 0.2 m ^?2. The average size of animals found in shallow water (coarse sediment), with low abundance, was markedly larger than that of those from deeper water. Adults from shallow water consisted of 49.5% females, but in deep water the corresponding figure was only 38.6%.According to the data, spawning in deep water occurred in June, August–September, and possibly also in January–February. The spawning period in shallow water was more diffuse and uncertain. The egg diameter of 123.75 (C.I. ± 1.59) μm, indicates a lecithotrophic development. Maturation occurred at a shell length of 10–13 mm, and the largest animal found was 34.3mm long. The shell of L. borealis grows allometrically.     

Simultaneous diffusion and convection in single breath lung washout

Two mathematical models of pulmonary single breath gas washout (one analytic, one numerical) are developed and their predictions compared with experimental data on human subjects. Weibel's 23 generation symmetric anatomical model is used as a guide to bronchial tree geometry. Experimental plots of nitrogen concentration versus volume expired, dead space versus breath holding time, and dead space versus tidal volume are compared with plots predicted by the models. Agreement is good. A plot of nitrogen concentration in the airways as predicted by the numerical model at different times during inhalation and exhalation of a single breath of oxygen is shown. Model predictions for changes in dead space with changes in washout gas and expiratory flow rate are discussed. Use of the analytic model for obtaining average values of the path length from mouth to alveoli in a given subject is discussed. To the extent of their agreement with experiment, the models provide a sound physical basis for the correlation of airway structure and function.     

Gravitational deposition in a rhythmically expanding and contracting alveolus.

In a previous simulation, our laboratory demonstrated that the flow induced by a rhythmically expanding and contracting alveolus is highly complex (Haber S, Butler JP, Brenner H, Emanuel I, and Tsuda A, J Fluid Mech 405: 243-268, 2000). Based on these earlier findings, we hypothesize that the trajectories and deposition of aerosols inside the alveoli differ substantially from those previously predicted. To test this hypothesis, trajectories of fine particles (0.5-2.5 microm in diameter) moving in the foregoing alveolar flow field and simultaneously subjected to the gravity field were simulated. The results show that alveolar wall motion is crucial in determining the enhancement of aerosol deposition inside the alveoli. In particular, 0.5- to 1-microm-diameter particles are sensitive to the detailed alveolar flow structure (e.g., recirculating flow), as they undergo gravity-induced convective mixing and deposition. Accordingly, deposition concentrations within each alveolus are nonuniform, with preferentially higher densities near the alveolar entrance ring, consistent with physiological observations. Deposition patterns along the acinar tree are also nonuniform, with higher deposition in the first half of the acinar generations. This is a result of the combined effects of enhanced alveolar deposition in the proximal region of the acinus due to alveoli expansion and contraction and reduction in the number of particles remaining in the gas phase down the acinar tree. We conclude that the cyclically expanding and contracting motion of alveoli plays an important role in determining gravitational deposition in the pulmonary acinus.     

Beyond the principle of similitude: renormalization in the bronchial tree

The average dimensions (diameter, length, and volume) of the airways in the mammalian bronchial tree, long thought to be exponential functions of the generation number, are shown to be power laws in generation number modulated by a harmonic variation. These data are satisfactorily described by means of a functional scaling relation--renormalization group property--between successive generations for the average variable of interest. This type of scaling may provide a mechanism for the morphogenesis of complex but highly stable structures.     

A reduction in the in situ rates of oxygen and glucose consumption of cells in EMT6/Ro spheroids during growth

The rates of consumption of oxygen and glucose by EMT6/Ro cells in multicellular spheroids were measured at various times during normal growth. In situ spheroid cellular consumption rates were similar to those of exponentially growing single cells up to a spheroid diameter of 150 micron. Further growth resulted in decreases in the rates of both oxygen and glucose consumption which were correlated with the increase in spheroid diameter and cell number. At a diameter of 1300 micron, both rates of cellular consumption had decreased by a factor of 2.5. The rates of consumption per unit of nonnecrotic spheroid volume decreased in a similar manner. Measurements with single cells demonstrated that the rate of oxygen consumption was coupled with glucose concentration, and vice versa. The rates of consumption for cells dissociated from small spheroids indicated that there was some effect of the spheroid environment. As the spheroids grew, however, association in the spheroid structure accounted for a smaller proportion of the total observed reduction in the rates of nutrient consumption. The presence of central necrosis also appeared to have no effect on the rates of consumption of these nutrients. Spheroid-derived cells showed a decrease in cell volume with growth as the cells accumulated in a quiescent state. Measurements with single cells demonstrated that oxygen and glucose consumption were correlated with cell volume and with the development of nonproliferating cells. We conclude that the observed decrease in oxygen and glucose consumption with growth in spheroids is largely due to the progressive accumulation of cells in a quiescent state characterized by an inherently lower cellular rate of nutrient utilization.     

Effects of treatment with noradrenaline and isoproterenol on the excretory portion of the submaxillary gland in the rat: an ultrastructural study

The aim of this study is to evaluate the modification of the excretory portion and its comparison with the acinus, on stimulating the rat submaxillary gland with noradrenaline and isoproterenol. Stimulation of the submaxillary gland with these drugs for a period of 10 min produces different effects in the acinus and excretory portion. The secretory granules do not show reorganisation of their contents after stimulation with isoproterenol, while in the acinus the material is reorganised forming concentric laminae. After stimulation with noradrenaline, the acinar lumen increases its diameter with respect to the control groups, while this same stimulus does not modify the diameter of the ductal lumen. After stimulation with noradrenaline, the extracellular spaces are consistently obliterated in all ducts except the striated duct, in which the behaviour is variable as in the acinus. In these two latter cases, the extracellular spaces are visible in some cases and not in others. Stimulation with noradrenaline is a potent stimulus of synthesis in both the granular undulated duct and the striated undulated duct, while in the acinus this effect is produced by isoproterenol.     

Enhancer of terminal gene conversion,a new mutation in Drosophila melanogaster that induces telomere elongation by gene conversion

Telomeres of Drosophila melanogaster contain arrays of the retrotransposon-like elements HeT-A and TART. Terminally deleted chromosomes can be maintained for many generations. Thus, broken chromosome ends behave as real telomeres. It was previously shown that gene conversion may extend the broken ends. Here we found that the frequency of terminal DNA elongation by gene conversion strongly depends on the genotype. A dominant E(tc) (Enhancer of terminal gene conversion) mutation markedly increases the frequency of this event but does not significantly influence the frequency of HeT-A and TART attachment to the broken chromosome end and recombination between directly repeated sequences at the end of the truncated chromosome. The E(tc) mutation was mapped to the 91-93 region on chromosome 3. Drosophila lines that bear the E(tc) mutation for many generations have telomeres, consisting of HeT-A and TART elements, that are longer than those found in wild-type lines. Thus, the E(tc) mutation plays a significant role in the control of telomere elongation in D. melanogaster.     

In situ oxygen consumption rates of cells in V-79 multicellular spheroids during growth

The rate of consumption of oxygen by V-79 cells in multicellular spheroids was measured as a function of the spheroid diameter. In situ consumption was equal to that of exponentially growing cells for spheroids less than 200 micron in diameter. The rate of oxygen consumption decreased for cells in spheroids between 200 and 400 micron diameter to a value one-fourth the initial, then remained constant with further spheroid growth. Comparison of consumption rates for spheroid-derived cells before and after dissociation from the spheroid structure indicated that the spheroid microenvironment accounted for only 20% of the change in oxygen consumption rate. Cell-cell contact, cell packing, and cell volume were not critical parameters. Plateau-phase cells had a fivefold lower rate of oxygen consumption than exponential cells, and it is postulated that the spheroid quiescent cell population accounts for a large part of the intrinsic alteration in oxygen consumption of cells in spheroids. Some other mechanism must be involved in the regulation of cellular oxygen consumption in V-79 spheroids to account for the remainder of the reduction observed in this system.