Scanning and transmission electron microscopic study of the lung of the newt,Triturus alpestris Laur.

Summary The lungs of Triturus alpestris Laur. were investigated with the scanning and transmission electron microscopes. Dimensions of the cell bodies of pneumocytes and ciliated cells, as well as the thickness of the air-blood barrier, were determined. The lungs of the newt form two simple sacs without septa. A ciliated epithelium containing goblet cells lines the pulmonary vein and partially the pulmonary artery. The remainder of the lung surface is covered internally by respiratory epithelium consisting of one type of cell and only occasionally showing the presence of single ciliated cells. All cells, ciliated, goblet and pneumocytes, contain in their cytoplasm lamellar bodies. Multivesicular bodies and numerous vesicles of variable electron density also occur in the cytoplasm of pneumocytes. Atypical mitochondria can be found in all cell types of the lung. Fixation with addition of tannic acid reveals the surface lining film. Tubular myelin figures were not observed.     

Morphological and pharmacological basis for pulmonary ventilation in Amphiuma tridactylum

Summary The lung of the giant salamander, Amphiuma tridactylum, is divided into respiratory alveoli by muscular septa that increase the surface area of the lung as well as provide a mechanism for its almost complete collapse during exhalation. The epithelium of the internal surface is of two types: respiratory, composed of a single layer of pneumocytes overlying anastomosing capillaries, and non-respiratory, composed of ciliated cells and mucus-secreting goblet cells. Non-respiratory epithelium covers the apical edges of the septa, whereas the respiratory epithelium lines the alveoli. The smooth muscle of the septa and walls of the lung was studied in preparations of uninflated and acetylcholine-contracted lung. The muscle cells are ultrastructurally similar to other types of smooth muscle but are surrounded by extraordinary amounts of extracellular matrix, containing collagen and elastic fibers and numerous fine fibrils of unknown composition. Smooth muscle in isolated lung strips contracted in a dose-dependent manner when treated with acetylcholine or methacholine; contraction was blocked by atropine. Responses of lung strips to adrenergic agents were limited; only high doses of adrenalin caused slight relaxation of previously contracted muscle. These observations support the hypothesis that contraction of pulmonary smooth muscle is responsible for the ventilatory efficiency of the lung.     

Interplay between the morphometry of the lungs and the mode of locomotion in birds and mammals

We studied the lung diffusion parameters of two species of birds and two species of mammals to explore how structural and functional features may be paralleled by differences in life style or phylogenetic origin. We used two fast-flying species (one mammal and one bird), one running mammal and one bird species that flies only occasionally as models. The harmonic mean thickness of the air-blood barrier was very thin in the species we studied. An exception was the Chilean tinamou Notoprocta perdicaria, which only flies occasionally. It showed an air-blood barrier as thick as that of flightless Galliformes. We found that the respiratory surface density was significantly greater in flying species compared to running species. The estimated values for the oxygen diffusion capacity, DtO2 follow the same pattern: the highest values were obtained in the flying species, the bat and the eared dove. The lowest value was in N. perdicaria. Our findings suggest that the studied species show refinements in their morphometric lung parameters commensurate to their energetic requirements as dictated by their mode of locomotion, rather than their phylogenetic origin. The air-blood barrier appears to be thin in most birds and small mammals, except those with low energetic requirements such as the Chilean tinamou. In the species we studied, the respiratory surface density appears to be the factor most responsive to the energetic requirements of flight.     

Lungs of the gecko Rhacodactylus leachianus (Reptilia: Gekkonidae): a correlative gross anatomical and light and electron microscopic study

The lungs of the New Caldeonian gecko Rhacodactylus leachianus were examined by means of gross dissection and light and electron microscopy. This tropical species, which is the largest living gecko, possesses two simple, single-chambered lungs. Right and left lungs are of similar size and shape. The lung volume (27.2 ml.100 g-1) is similar to that of the tokay (Gekko gecko) but differs in that the gas exchange tissue is approximately homogeneously distributed, and the parenchymal units (ediculae) are very large, approximately 2 mm in diameter. The parenchymal depth varies according to the location in the lung, being deepest near the middle of the lung and shallowest caudally. Scanning and transmission electron microscopy reveal an unusual distribution of ciliated cells in patches on the edicular walls as well as on the trabeculae. Secretory cells are very numerous, particularly in the bronchial epithelium, where they greatly outnumber the ciliated cells. The secretory cells form a morphological continuum characterized by small secretory droplets apically and large vacuoles basally. This continuum includes cells resembling type II pneumocytes but which are devoid of lamellar bodies. Type I pneumocytes similar to those of other reptiles cover the respiratory capillaries, where they form a thin, air-blood barrier together with the capillary endothelial cells and the fused basement laminae. The innervation, musculature, and vascular distribution in R. leachianus are also characterized. Apparent simplification of the lungs in this taxon may be related to features of its sluggish habits, whereas peculiarities of cell and tissue composition may reflect demands of its mesic habitat.     

Adaptations to the air breathing in the posterior intestine of the catfish (Corydoras aeneus,Callichthyidae). A histological and ultrastructural study

A light and transmission electron microscopic study of the intestine of catfish C. aeneus shows that the anterior part of the intestine is a site of digestion and absorption and its structure is typical of that of other teleostean fishes. However, in this species the thin-walled posterior intestine is adapted to air breathing. In this region mucosa is smooth and lined with respiratory epithelium with capillary network. Several types of cells are observed in the epithelium: flattened respiratory epithelial cells with short microvili, goblet cells, scarce epithelial cells with numerous longer microvilli, and two types of endocrine cells (EC). The solitary brush cells with several long and thick microvilli described here are the first observation of such cells in the gastrointestinal tract of fishes. Bodies of respiratory epithelial cells lie between capillaries. Their cytoplasm, apart from typical organelles contains dense and lamellar bodies, which are a site of accumulation of surfactant. In regions where capillaries are covered by thin cytoplasmic sheets of respiratory epithelial cells, a thin (0.24-3.00 microm) air-blood barrier is formed, thus enabling gas exchange. Epithelial cells with longer microvilli do not participate in the formation of the air-blood barrier and are probably responsible for absorbtion. EC of the closed type are dispersed within the epithelium. Their cytoplasm contains characteristic round or oval dense core vesicles 69 to 230 nm in diameter. The role of EC and brush cells in the regulation of processes related to absorbtion, and to respiration, is disscused.     

The morphology of the lung of a tropical terrestrial slug Trichotoxon copleyi (Mollusca: Gastropoda: Pulmonata): A scanning and transmission electron microscopic study

The lung of the slug Trichotoxon copleyi is located in the body mantle where it opens to the outside through an adjustable pneumostome situated on the right side. The respiratory surface of the lung is profusely vascularized by anastomosing 'blood' capillaries. A thick muscular layer surrounds the gas exchange surface and may be involved in the efficient rhythmic ventilatory contraction of the lung. Externally an epithelial layer made up of large secretory cells with numerous microvilli overlies the muscular layer. The surface of the lung is made up of squamous cells with an abundance of microvilli and clustered goblet cells interspersed occasionally. The squamous cells cover the notably thin air–blood barrier which is extremely attenuated, particularly in some areas. The goblet cells contain a centrally located nucleus and numerous intracytoplasmic granules, presumably precursors of the mucus that covers the surface of the mantle cavity.
All the essential morphological prerequisites for efficient gas exchange such as an extensive surface and a thin blood–gas barrier were observed in the lung of Trichotoxon. It was concluded that this molluscan lung is structurally and functionally a true lung in all respects.     

Effect of the antihypoxic agent ionol on the morphofunctional state of the air-blood barrier of the lungs in hypoxic anoxia

It is shown that antihypoxic ionol has promoted normalization of the air-blood lung barrier ultrastructure, activation of the surfactant system under acute hypoxic hypoxia effect as well as compensatory redistribution of the thickness of separate barrier layers due to intensified synthesis of phospholipids which are the components of cytoplasmic membranes and pulmonary surfactant.     

Brush-like cells within bronchial epithelia of chicken lung (Gallus gallus)

The secondary and primary (mesobronchus) bronchi of chicken lung are lined by a typical respiratory epithelium: pseudostratified columnar ciliated with goblet cells. Up to date, four constituting epithelial cell types have been identified: ciliated, mucosecretory, basal and endocrine cells. In this study a putative new epithelial cell type, the brush-like cell, is described. The avian brush-like cells have only been found in the bronchial epithelia but never in the gas-exchange areas. They are scattered among the other epithelial cells, mainly ciliated cells, and their number is extremely low. The characteristic morphological feature of these cells is an apical protruding cytoplasm with microvilli. This cell type is similar to that found in the lung of some mammalian and non-mammalian species. The functional role of these cells is not yet clear; they could carry out absorptive processes.     

Ultrastructure of the blood-air barrier in comparison with the indices of surfactant surface activity

Ultrastructure of the air-blood barrier and surface surfactant activity were studied at different time periods of nonspecific inflammation of the lungs in guinea pigs. The animals were sacrificed 3 days, 2 weeks and 1, 2 and 4 months after beginning of the experiment. It has been demonstrated that in early periods of lung inflammation there was edema of all components of the air-blood barrier. Subsequent development of inflammation is accompanied by surface activity decrease associated with dystrophic changes in the epithelial cells of alveoli. At the same time there are compensatory changes in the lungs, directed to eliminate deficiency of surfactant.     

Morphology and morphometry of the normal lung of the adult vervet monkey (Cercopithecus aethiops)

The lungs of four adult specimens of the vervet monkey (Cercopithecus aethiops) have been examined by transmission and scanning electron microscopy. A morphometric evaluation of the structural components directly involved in gas exchange has been carried out and the data have been modelled to estimate the anatomical diffusing capacity of the lung. The upper air-conducting airways of the lung were lined by an epithelium characterized by ciliated cells among which were dispersed goblet cells. The alveolar surface was lined by squamous type I pneumocytes and cuboidal type II granular pneumocytes. The blood-gas (tissue) barrier consisted of an epithelial cell, a common basal lamina, and an endothelial cell in the thin parts of the interalveolar septum. In the thicker parts of the septum, an interstitial space interposed between the basal laminae of the epithelial and endothelial cells contained supportive elements such as collagen, elastic tissue, and fibrocytes. The alveoli, the blood capillaries, and septal tissue composed 73%, 16%, and 11%, respectively, of the parenchyma. The harmonic and arithmetic mean thicknesses of the blood-gas (tissue) barrier were 0.311 micron and 1.048 microns; the surface area of the blood-gas (tissue) barrier per unit body weight was 50 cm2g-1, and the surface density was 117 mm2.mm3-1. The weight-specific total morphometric diffusing capacity was 0.11 mlO2 (sec.mbar.kg)-1. In comparison, the pulmonary morphometric characteristics of vervet monkey lung were superior to those of the other primates (Macaca irus, M. mulatta, and Homo sapiens) for which equivalent data are available. The gas-exchange potential of the lungs of the nonhuman primates as revealed by morphometric studies surpasses that of man, a feature that can be attributed to the relatively less energetic human lifestyle.     

Freeze-fracture replica studies of tight junctions in normal human bronchial epithelium

Using freeze-fracture techniques, tight junctional networks were observed in the human normal bronchial epithelium. They were morphologically classified into three types: type I was a loosely interconnected, most complicated network consisting of 7-11 roughly parallel wavy strands and situated between ciliated cells; type II was a randomly anastomosing, simple network made up of 2-4 strands and present between goblet cells; type III was an irregularly anastomosing network composed of 4-7 strands and located between a ciliated cell and a goblet cell. Type III junctions, when a goblet cell was strongly bulged, were located on the swollen ridge, the upper surface of which was separated by a deep groove from the bulged apical surface, around the lateral surface of the cell at the level of the luminal surface. The possible relation between the orientation of strands of these networks and extra- or intracellular stress was discussed.     

A MORPHOMETRIC STUDY ON THE THICKNESS OF THE PULMONARY AIR-BLOOD BARRIER

A reliable knowledge of the thickness of the alveolo-capillary "membrane" or air-blood barrier is of physiologic interest since it is intimately related to a quantitative estimation of such functional events as gas diffusion or tissue metabolism in the lung. The characteristic thickness of the air-blood barrier with respect to gas diffusion is its harmonic mean thickness, while the arithmetic mean thickness is related to the mass of tissue building the barrier and consuming oxygen in the lung. Two morphometric methods are proposed by which these two dimensions can be estimated from random measurements in the electron microscope in a reliable, simple, and efficient manner. By applying these methods to three rat lungs the arithmetic mean thickness of the barrier was found to measure 1.25 µ, the harmonic mean thickness, 0.57 µ. On the basis of these measurements a geometric model of the barrier in the form of a corrugated membrane was derived. Its dimensions showed close similarity to those of the natural barrier. This analysis suggested furthermore that the gas conductance of the barrier is nearly optimal if one considers the mass of tissue and the minimal barrier thickness as fixed properties which are determined by other functional requirements on the alveolo-capillary membrane.     

Gas exchange morphometry of the lungs of the tokay,Gekko gecko L. (Reptilia: Squamata: Gekkonidae)

The tokay lizard (Gekko gecko) possesses singlechambered lungs, eacch of which is a mirror image of the other reflected in the midsagittal body plane. When standard techniques are employed for instilling 2% phosphate-buffered glutaraldehyde to three-quarters of the total lung capacity, neither the left nor the right lung is consistently larger. Internally, the lungs are characterized by a row of 11 dorsomedial niches and by honeycomb-like (faveolar) gas exchange tissue, which is deeper cranially than caudally. Based upon mean values for all experimental animals, a 100-g tokay would have an overall anatomical diffusion factor (respiratory surface area divided by the appropriate _ht) of 203 cm²·m^-1·100 g^-1, 61% of which is located on the interfaveolar septa. Of the total septal anatomical diffusion factor, 94% is evenly divided between the anterior and middle thirds of the lung, with 6% in the posterior third. The 39% of the anatomical diffusion factor located on the inner lung wall is predominantly (76%) in the middle and posterior lung thirds, with only 24% in the anterior region. These tendencies toward heterogeneous distribution of anatomical diffusion factor were most pronounced in a 55 g juvenile animal. In this animal the total anatomical diffusion faxtor/body mass was 3.6 times that of a 197 g adult. This difference was attributable to a greater body massspecific lung volume and respiratory surface area as well as to a greater surface-to-volume ratio in the parenchyma and to a thinner air-blood diffusion barrier in the juvenile animal.Abbreviations ADF anatomical diffusion factor - %AR percentage of potential respiratory surface area which makes up S_AR - DtO₂ diffusing capacity for air-blood tissue barrier - IUR isotropic uniform randomly distributed - bm body mass - %P percentage of lung volume devoted to parenchyma - S _A potential respiratory surface area (S _L minus the surface area of the trabeculae) - S _ANR non-respiratory surface area - S _AR respiratory surface area - S _L total internal surface area of the lung - S _v surface area-to-volume ratio in parenchyma - _ht harmonic mean thickness of the air-blood tissue barrier - V _L morphometrically determined volume of both lungs, fixed at 0.75· V _Lm - V _Lm maximal lung volume, similar to total lung capacity in mammals - V _Lr resting lung volume, similar to functional residual capacity in mammals - VP morphometrically determined volume of parenchyma of both lungs, fixed at three-quarters of V_Lm     

In vitro-generated respiratory mucosa: a new tool to study inhalational anthrax

We generated a three-dimensional (3-D) model of human airway tissues in order to study initiation of inhalational form of anthrax infection. The system was designed to model the air-blood barrier of the respiratory tract represented by epithelial cells and macrophages. When grown on collagen/fibronectin gel support at an air-liquid interface, airway epithelial cells formed cell layers morphologically resembling those in vivo. These preformed epithelial cell cultures were further supplemented with monocytes/macrophages isolated from human blood. After 2-5 days of co-culture, monocytes differentiated into a phenotype of resident macrophages, which was evaluated by the expression of specific cell surface markers. This model allowed sorting out the role of each type of cell found at the air surface of the lung. The interdependence of macrophages and epithelial cells in the clearance of anthrax spores from airways and the capacity of the airway epithelial cells to protect from anthrax infection was demonstrated.     

The state of the "glycocalyx" of rat lung cells following left-sided pneumonectomy]

Edema in the tissue of the right lung developed 24 hours after the leftsided pneumonectomy. It was found that: 1) the layer of acid mucopolysaccharide on the surface of the alveolar and endothelial cells became thicker; 2) accumulation of the product of reaction with the RR on the surface of the alveolar cells of type 1 and of the endothelial cells took place; 3) "blisters" coated with the product of reaction with the RR (Red Ruthenium) appeared. These "blisters" were connected with the plasmolemma of the alveolar and endothelial cells. All these findings suggest that acid mucopolysaccharides of the lung surfactant system participated in the accumulation and elimination of the water from the tissues of the air-blood barrier.     

Ultrastructure of cell types of the olfactory epithelium in a catfish,Heteropneustesfossilis (Bloch)

Transmission electron microscopical study of olfactory epithelium of a mud-dwelling catfish,Heteropneustes fossilis (Bloch) shows receptor, supporting, goblet and basal cells. The receptor cells are of ciliated and microvillous type. Both ciliated and microvillous receptor cells are provided with olfactory knob. The dendrite of all the receptor cells bears many longitudinally arranged microtubules. Occurrence of the rod cell and its function is quite debatable. Specialized juctional complexes between the receptor and adjacent cells are clearly noted. The supporting cells are both ciliated and nonciliated. The ciliated supporting cells are responsible for water ventilation in the olfactory chamber as well as in the inter-lamellar spaces. This facilitates better perception of odours by the receptor cells. In addition to providing mechanical support to other cells, the nonciliated supporting cells also have a secretory function which is evident from the present study. The different stages of maturity of goblet cells are well documented. The presence of white cells in the olfactory epithelium is a very rare finding.     

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.     

Morpho-functional analysis of lung tissue in mild interstitial edema

Mild pulmonary interstitial edema was shown to cause fragmentation of interstitial matrix proteoglycans. We therefore studied compartmental fluid accumulation by light and electron microscopy on lungs of anesthetized rabbits fixed in situ by vascular perfusion after 0.5 ml.kg(-1).min(-1) iv saline infusion for 180 min causing approximately 6% increase in lung weight. Morphometry showed that a relevant portion (44%) of extravascular fluid is detected early in the alveolar septa, 85% of this fluid accumulating in the thick portion of the air-blood barrier. The arithmetic mean thickness of the barrier increased in interstitial edema from 1.06 +/- 0.05 (SE) to 1.33 +/- 0.06 microm. The harmonic mean thickness increased from 0.6 +/- 0.03 to 0.86 +/- 0.07 microm, mostly due to thickening of the thin portion causing an increase in gas diffusion resistance. Despite some structural damage, the air-blood barrier displays a relatively high structural resistance providing a safety factor against the development of severe edema. It is suggested that the increase in extra-alveolar perivascular space occurs as a consequence of fluid accumulation in the air-blood barrier.