Neuroendocrine epithelial cells in the broncho-parabronchial transition of embryonic, immature and mature quail (Coturnix coturnix).

The main objective of this integrated light microscopic, transmission and scanning electron microscopic study was to describe in greater detail the structural pattern and developmental stages of pulmonary neuroendocrine epithelial cells (PNECs) in the broncho-parabronchial transition (BPT) of both developing and mature quail. In mature quail the BPT appeared as a diaphragm opening into the parabronchial vestibulum. Perpendicular sections revealed two bilayered crest-like entrance folds invested by a uniform population of granular cells with lamellar bodies and a brush border of blunt microvilli. Solitary PNECs were found interlaced between the granular cells on both sides of the BPT. In addition, PNECs with small dense-cored vesicles (DCVs) were found subepithelially in the lamina propria mucosae of the parabronchial compartment of the BPT, which was surrounded by a capsule of granular cells. Furthermore, clusters of PNECs devoid of any epithelial capsule, but with large DCVs were located in the tunica propria mucosae. The first signs of the developing BPT could be identified as early as embryonic day (ED) 13. By ED 17, the area of the future BPT was seen to be invested by a uniform population of granular cells but the entrance fold proper did not appear until after hatching. Solitary or clustered PNECs were demonstrated in parabronchial buds growing into the mesenchyme on ED 12 and 13: either type I PNECs with small DCVs measuring about 80-120 nm or type II PNECs with large dense granules measuring approximately 150-280 nm. Both types of PNECs represented a temporary cell population in the prehatching period. In the parabronchus no PNECs or neuroendocrine epithelial bodies could be demonstrated in mature and immature quail beyond the BPT.

Lamellar inclusions and trilaminar substance in the parabronchial epithelium of the quail (Coturnix coturnix).

The fine structure of the epithelial cells of the parabronchus and their secretory products have been the subject of many studies and have given rise to considerable controversy about their configuration and ultrastructure. The aim of the present study was to investigate the mode of formation and discharge of lamellar bodies of granular cells and the trilaminar substance produced and discharged by the embryologically related squamous atrial and respiratory epithelial cells. The material for light and transmission electron microscopic analysis was collected from 10 mature quail and 3 individuals aged 2 days. The parabronchial atria harbour two ultrastructurally distinct types of epithelial cells. The granular cells (analogous to type II cells of the mammalian pulmonary alveolus) produce and discharge balls of lamellar bodies. The squamous atrial cells produce and discharge sheets of trilaminar substance sandwiched between long tentacle-like processes, viz. the microvilli. The infundibula and air capillaries of the gas exchange tissue are invested with squamous respiratory cells which extend very thin, long processes that cover the air capillaries and constitute, together with the blood capillaries, the blood-air barrier. The squamous respiratory cells produce and discharge trilaminar substance as an extracellularly located acellular lining layer which is found in close contact with their cell membrane. Both squamous atrial and respiratory cells hence synthetize and discharge trilaminar substance, the basic unit of which has the ultrastructural appearance of a 7.5 to 8.0 nm membrane unit. The formation of trilaminar substance originates in the agranular endoplasmic reticulum, while the origin of the lamellar bodies of granular cells is related to the granular endoplasmic reticulum, the Golgi complex and the multivesicular bodies. Their structural unit is composed of a 4.5 to 5.0 nm thread-like structure which is concentrically arranged around a spherical core of granular substance.

A scanning and transmission electron microscopy study of the parabronchial unit in quail (Coturnix coturnix) and town pigeons (Columba livia).

A combined scanning electron (SEM) and transmission electron microscopy (TEM) investigation was undertaken to gain insight into the complex structural pattern of the atrial compartment and the gas exchange tissue of parabronchial units in quail and town pigeons. The aim was also to depict the changes taking place in the parabronchial unit in the late prehatching and early posthatching periods in quail. The standard SEM and TEM investigation was carried out in 13 mature quail and 8 town pigeons. The developmental study involved embryonic quail (Days 15, 16, 17), newly hatched quail, quail 24 h after hatching, and quail aged 2, 10, 19, and 25 days (3 individuals per group). The luminal relief of the parabronchus is formed by anastomosing interatrial septa delineating the atrial pits, which are thinner and shallower in pigeons. The atrial bottom opens in mature individuals into 3-6 infundibula. The extracellular material represented by trilaminar substance, which does not appear until hatching, veils the surface relief of the parabronchial epithelium, which is consequently hardly accessible to three-dimensional visualization. Only in town pigeons with fewer discontinuous layers of extracellular material was it possible to visualize the surface of the atrial epithelium, that is, of the granular and squamous atrial cells. The SEM analysis has convincingly shown the intricate spatial organization of atria, infundibula, and air and blood capillaries of the gas exchange tissue. The retinacula, that is, parallelly arranged processes of squamous respiratory cells bridging the air-capillary lumina, were evidenced by SEM and TEM. The complex structure of the avian parabronchus has been successfully demonstrated in the present SEM and TEM study.

An SEM and TEM study of the transition of the bronchus to the parabronchus in quail (Coturnix coturnix).

The main objective was to analyse the transition of the bronchus to the parabronchus in birds and to describe its specific structure in an integrated light microscopic, transmission electron microscopic (TEM) and scanning electron microscopic (SEM) study. Lung tissue from immature and mature quail was subjected to standard processing for paraffin light microscopy, TEM and SEM after intratracheal inflation with fixative. In transverse paraffin and Durcupan semithin sections, the partition incompletely closing the broncho-parabronchial transition has the appearance of a crest-like fold delineating the entrance to the underlying parabronchial vestibulum. The core of the entrance fold is composed of loose connective tissue with free cells, and has a well-developed blood supply and innervation. Voluminous groups of smooth muscle cells are interconnected with those of neighbouring entrance folds and the interatrial septa. On the parabronchial surface and partly on the bronchial surface the entrance fold is invested with simple cuboid epithelium consisting exclusively of granular cells with lamellar inclusions. On the bronchial surface, they pass into ciliated columnar pseudostratified epithelium. At the root of the parabronchially orientated surface, they continue into the mixed population of granular and squamous atrial cells of the parabronchus. Among the granular cells of the entrance fold, scattered epithelial neuroendocrine cells are consistently present. The three-dimensional visualization demonstrated the oval form of the entrance window with a circular field of non-ciliated cells delineating the entrance to the parabronchial labyrinthine system. The general structural pattern of the entrance fold, together with the complex system of interatrial trabecles of the parabronchi underline the multifactorial function of a complex system submitted to the skeletal, regulatory and host defense of the gas exchange tissue.

The development and differentiation of the parabronchial unit in quail (Coturnix coturnix).

The present study has been inspired by the conflicting data in the relevant literature concerning the embryogenesis of cell types of the parabronchial epithelium and the formation, discharge and distribution of trilaminar substance and lamellar bodies. Lung tissue from embryonic, newly hatched, immature and mature quail was subjected to standard processing for light and transmission electron microscopy. The parabronchial rudiments form shallow primitive atria on embryonic day 13. The precursors of granular cells differentiate with lamellar bodies in their cytoplasm. The residual population of non-granular epithelial cells is the common source for the differentiation of primitive squamous atrial and respiratory cells, the potential producers of trilaminar substance. The primitive squamous atrial cells sprout as branching infundibular canaliculi into the mesenchyme on embryonic day 14. The infundibular epithelium differentiates into the squamous respiratory cells that constitute with blood capillaries the blood-air barrier. Not until the time of hatching could the trilaminar substance be visualized being produced by squamous atrial and respiratory cells. In the late prehatching and early posthatching period the granular cells intensely escalate the production and discharge of lamellar bodies. The lamellar bodies form, together with sheets of trilaminar substance, mixed multilayered masses in atria. They disappear fast in the successive posthatching period. The formation of trilaminar substance in squamous atrial and respiratory cells is governed by the agranular endoplasmic reticulum, the cisternae of which take part in the formation of trilaminar units. The gas exchange tissue is predominantly represented by infundibula in immature quail. The posthatching growth of the gas exchange tissue of immature to mature quail occurs via intense multiplication of air and blood capillaries.

An electron microscopic study of the parabronchial epithelium in the mature lung of four bird species.

BACKGROUND: No integrated comprehensive description of the ultrastructure of the parabronchial epithelium is available. The origin, discharge, and occurrence of the trilaminar substance have not yet been sufficiently studied. Therefore, the main objectives were to classify the cell types of the parabronchial epithelium and to describe their role in manufacturing the trilaminar substance. METHODS: Lung tissue of mature quail, domestic fowl, town pigeon, homing pigeon, and barn owl was subjected to standard processing for transmission electron microscopy, both after intratracheal inflation and intravascular perfusion. RESULTS: The atrial epithelium is constituted by granular and squamous atrial cells. Granular cells (1) are confined to the atrial wall; they produce and discharge osmiophilic lamellar bodies. Squamous atrial cells (2) manufacture and discharge a trilaminar substance in sheets sandwiched between the long microvilli emerging from the apical cytoplasm. Their attenuating cell outgrowths overlap granular cells. At the bases of atria, they pass as intermediate squamous atrial cells to the infundibula, contacting the extensions of squamous respiratory cells. The squamous atrial cells undergo distinct structural variations depending on age and environment. Squamous respiratory cells (3) (cellulae squamosae) continuously line the air capillaries and neighboring infundibula. They constitute the epithelial compartment of the blood-gas barrier. The cell bodies extend long, very thin cell outgrowths. The apical surface is smooth and the basal part is invested with a very thin basement membrane. The trilaminar substance originates from granular and agranular endoplasmic reticulum in the form of convoluted profiles which are discharged as an acellular lining layer on the air surface of squamous respiratory cells. CONCLUSIONS: Granular cells are analogous to the type II cells of mammalian pulmonary alveolus. Squamous atrial and respiratory cells, of a common embryonic origin, do not meet any counterpart in epithelial cell populations of lung terminal airways in vertebrates. The specific trilaminar substance--lipoproteinaceous in nature--is a constant compound of atria and air capillaries.

Anchoring and support system of pulmonary gas-exchange tissue in four bird species.

Avian air capillaries are delicate structures compared to the mammalian pulmonary alveolus. A transmission and scanning electron microscopic study was carried out on several species of birds with the aim of determining the support structures of the avian gas-exchange mantle. Lung tissue of two bird species belonging to strong flying birds (pigeon and barn owl) and two relatively flightless species (domestic fowl and quail) was subjected to standard processing for transmission and scanning electron microscopy after intratracheal inflation. Twisted profiles of lipoproteinaceous trilaminar substance as specific secretory product of avian squamous respiratory cells can be seen in the cell body and cytoplasmic extensions that are wedged between the blood capillaries, partly surrounding them. The intracytoplasmatically located trilaminar complexes form a three-dimensional intricate spiderweb-like system between the blood capillaries and air capillaries, which presumably function as an anchoring and support structure of the gas-exchange tissue. This system is strengthened by retinacula--pairs of attenuated parallel processes of squamous respiratory cells that project to the airway lumen--expanding and bridging the opposite side of air capillaries. The trilaminar substance is discharged in the form of a 15-nm-thick acellular lining layer which is uniquely adapted to the extremely thin respiratory epithelium. The trilaminar substance arises in the cytoplasm of squamous respiratory cells from profiles of granular and smooth endoplasmic reticulum. The integrity and stability of the gas-exchange tissue is likely to be guaranteed by a specific arrangement of the squamous respiratory cells, in which the trilaminar substance plays a paramount role. This general pattern can be observed in strong flying bird species as in the relatively flightless birds.

Lymphatics in the lung of a precocial bird before and after hatching.

A light and electron microscopic study of pulmonary lymphatics was carried out in quail embryos (embryonic day; ED 13-17), completed with samples of lungs of quail 90 min, 24 h after hatching and two 2-day-old and three adult quail. The aim of the study was to depict the morphology of pulmonary lymphatics by determining the dynamics in ontogeny and to establish the rules of their distribution. The primitive lymphatics appear on ED 13 and 14 as closed thin-walled tubes in abundant interparabronchial mesenchyme. They seemingly differentiate from the mesenchymal cells. Due to the proliferation, growth, and enlargement of the parabronchial compartments, the interparabronchial septa disappear to a large extent, and the external walls of parabronchi appose and join. On ED 16 and 17, the mesenchyme is squeezed to the trigonal fields among the neighboring parabronchi. The lymphatics form broad, voluminous lakes around the arteries; on the other hand, they are also found in close contact with the gas exchange tissue as juxta-air capillary lymphatics. After hatching, the former interparabronchial septa disappear, and the imaginary boundary between parabronchi is demarcated by interparabronchial arteries and veins. The lymphatics are confined to the adventitial connective tissue which conducts the larger arteries and veins of the original trigone of the interparabronchial septa. The richly vascularized parabronchi in mature quail are poor in connective tissue and to a large extent devoid of lymphatics, in comparison to the mammalian lung where the lymphatic capillaries have their roots at the level of the respiratory bronchioles. The avian pulmonary lymphatics serve as an appropriate model for the analysis of principles controlling the origin and distribution of lymphatics in general.

Pulmonary macrophages in birds (barn owl, Tyto tyto alba), domestic fowl (Gallus gallus f. domestica), quail (Coturnix coturnix), and pigeons (Columbia livia).

BACKGROUND: Birds have a limited number of resident macrophages in the normal steady-state respiratory tract. The discovery of phagocytes in lavages of lung from birds contrasts with findings that phagocytes are seldom seen in investigations in situ. An electron microscopic study was performed in the respiratory units, the parabronchi, and air capillaries in particular in several adult bird species to localize the seat of respiratory macrophages. METHODS: Lung tissue of barn owl, domestic fowl, quail, and town and homing pigeons was subjected to standard processing for light and electron microscopy after immersion fixation, intratracheal instillation, and intravascular perfusion. RESULTS: Clusters of macrophages were predominantly housed in the loose connective tissue at the floor of atria at the entrance to the infundibula and gas-exchange tissue proper. Scattered solitary phagocytes were also found in connective tissue of air sacs, interatrial septa, and adventitia of inter- and intraparabronchial arteries and veins and in peribronchial lymphoid tissue. Phagocytized foreign particulate material mostly consists of hard, dense, crystalline formations surrounded by a limiting membrane. The transport of small airborne particles occurs via the squamous atrial epithelium to the underlying macrophages. The macrophages are often accompanied by mast cells. CONCLUSIONS: The present results demonstrate that avian respiratory macrophages are predominantly located in atrial connective tissue compartments and do not seem to migrate to the airway surfaces.

[Early changes in the structure of venous grafts, their prevention and significance]. / Casné zmeny struktury zilních stepu, jejich prevence a význam.

The authors investigated, using optic and electron microscopy, the course of regressive changes in smooth muscle cells of the media in venous grafts, in relation to various physical and chemical factors. They recorded the influence of a temperature of 4 degrees C and 22 degrees C, the influence of various types of crystalloid and colloid solutions and some pharmaceutical preparations. In previous work they found that, as a result of ischaemia, regressive changes take place in the smooth muscle cells of the media, while plasmatic structures of these cells and fibrillar structures of the venous wall remain intact. They provided evidence of the adverse effect of crystalloids, where the regressive changes can be detected already after 30 minutes. A protective effect on the nuclear structure is exerted by colloids, in particular a 6% solution of detoxicated haemoglobin. More favourable results were achieved at 22 degrees C. Some pharmacological preparations have a favourable effect on the preservation of the structure of cellular nuclei. The authors draw attention to the importance of these changes for clinical practice.

[Early changes in the structure of vein grafts and their significance in the development of complications after revascularization surgery]. / Casné zmeny struktury zilních stepü a jejich význam pri vzniku komplikací po revaskularizacních operacích.

By means of light and electron microscopy the development of regressive changes in the media of vascular graft were studied. The authors found out that as a result of warm and cold ischaemia to which the vascular graft is exposed before implantation changes in nuclei of smooth muscle cells arise. The development of these changes can be postponed by keeping the graft in a suitable medium before implantation. Such medium may be e.g. the patient's blood cooled to 4 degrees C. On a group of their own patients the authors pointed out the significance of these changes in the development of early complications after vascular graft implantation.

[Fine morphology of the lymphatics and tissue spaces in the liver parenchyma in man and its significance in hepatobiliary surgery]. / Jemná morfologie lymfatik a tkánových sterbin jaterního parenchymu cloveka a její význam pro hepatobiliární chirurgii.

The authors investigated the intrahepatic lymphatic vessels of the human liver under a light and electron microscope. The histological material was obtained from 10 patients operated on account of simple cholecystolithiasis. The beginnings of the lymphatic capillaries are in the periphery of the perilobular connective tissue of the portobiliary space in the vicinity of openings of Mall's space. Communication between lymphatic capillaries and Mall's space was not proved. The fine structure of the openings in Mall's space with numerous microvilli of hepatocytes pointing towards the perilobular connective tissue were described. Mall's space communicates and is interconnected in a multiple way with intercellular spaces between neighbouring hepatocytes. Here also the plasmalemma of hepatocytes forms a system of microvilli which form the borderline of the interhepatocytic space. The ultrastructure of both systems of spaces corresponds to the pattern on the hepatocyte surface in Disse's perisinusoid space. The cell population of hepatocytes holds a special position because it lacks the lamina basalis as a selective barrier against the connective tissue interstitium. This structural specificity indicates the extensive and rapid transport of lymph via the perisinusoid Disse spaces into the blood stream of the hepatic sinusoids, also lacking lamina basalis. Mall's space and the system of interhepatocytic spaces form a continuous system which is in close but not direct contact with the incipient intrahepatic lymphatic capillaries.

Relationship between the saccus endolymphaticus and the fourth ventricle of the brain of the domestic fowl (Gallus gallus f. domestica).

The fine structure of the wall of the SE was determined exactly and its relationship to the cisternae (the evaginations of the roof of the fourth ventricle extending to the SE) was defined. The way in which the cisterna is formed was defined and the development of its fine structure was described by comparing serial sections from 19-day embryos and adult fowls. Like the SE, the cisternae are lodged in the angle between the cerebellum and the medulla oblongata, in the subarachnoid space. The terminal segment of the cisterna lies in the immediate vicinity of the mesenchymal epithelium bordering the basal labyrinth of the SE cells. Collagen trabeculae keep the SE and the cisternae suspended in the subarachnoid space. The cisternae and trabeculae are wrapped in mesenchymal epithelium. The cisterna is avascular and does not communicate with the SE. The cisterna is lined internally with simple squamous epithelium (modified neural epithelium of the roof of the fourth ventricle). The bodies of the cells bulge into the lumen of the cisterna in the region of localization of their nucleus. The epithelium is seated on a pronounced basal lamina. The surface turned towards the subarachnoid space is lined continuously with mesenchymal epithelium without a basal lamina. The cells of the cisternal epithelium are connected by tight junctions of the type of zonulae occludentes and desmosomes. The basal lamina is continuous and distinct. The mesenchymal epithelium of the subarachnoid space has no basal lamina, as on the subarachnoid surface of the SE, the cisternae, the trabeculae, the pia mater and the arachnoidea.(ABSTRACT TRUNCATED AT 250 WORDS)

[Ultrastructure of the air-blood-intestinal respiration barrier of the American sheatfish Hoplosternum thoracatum]. / Die Ultrastruktur der Luft-Blut-Darmatmungsbarriere des amerikanischen Welses Hoplosternum thoracatum.

The fish, Hoplosternum thoracatum, lives in water with a permanently reduced content of oxygen. The respiratory gut as an accessory respiratory organ makes it possible to breath atmospheric oxygen and facilitates gaseous interchange. It forms a large, dilated tube containing a voluminous bubble of air. The wall of the respiratory gut is extremely thin. Below the peritoneum there is situated a branching plexus of blood vessels. The tributaries extent perpendicularly and reach the epithelium. They form a rich anastomosing capillary network. The capillaries are covered with attenuated processes of squamous epithelium. The thickness of epithelial processes ranges roughly from 0.5-1.0 micron. The basal part of the respiratory epithelium is lined with basal lamina which, in many places fuses with basal lamina of the capillary endothelium. The air-blood barrier of the respiratory gut is, in principle, built up according to the known general bauplan and is formed by thin epithelial and endothelial components and complex of basal laminae. The nonrespiratory area of the gut is lined with columnar epithelium of enterocyte type.

[Changes the structural elements of the organs of bats during periods of activity and hibernation]. / Izmeneniia strukturnykh élementov organov u letuchikh myshei v periody aktivnosti i gibernatsii.

In hibernated animals (Myotis myotis) morphological changes are characterized by certain peculiarities in structure of the mitochondrial apparatus and some other cellular organells. In the animals, which are in the state of hibernation, the main plan of cardiomyocytes structure in the pulmonary vein wall, as well as in the myocardium itself does not change, as compared to those in the animals which are in the active state. The ultrastructure of the skeletal muscle fibers also does not undergo any essential alterations. A definitely seen narrowing of the capillary bed in the pulmonary alveoli is revealed. In the nuclei of their granular cells chromatin is substituted for lamellar myelin-like corpuscles; in cytoplasm there are inclusions that contain electron-opaque material of lamellar structure. In the active animals the inclusions contain electron-transparent material and are surrounded with a wide osmiophilic rim. In the liver of the hibernating animals hepatocytes loose their glycogen, but the number of lipid vacuoles and electron-opaque multivesicular corpuscles increase.