Air Capillaries Research Articles

A scanning electron microscope study of the microvasculature of the avian lung.

1. The microvasculature of the lung of the duck and pigeon was studied by scanning electron microscopy of vascular casts and critical point dried preparations of the gas exchange tissue. 2. The gas-exchange cappilaries are discrete tubular vessels intimately associated with air capillaries in a three dimensional network. 3. The capillaries originate from arteries at the periphery of the parabronchus, and are collected by veins which run close to its luminal surface. 4. The capillary bed of 3-5 atria is drained by a single vein. It is suggested that the vein and its associated capillaries may form a controllable subunit of pulmonary perfusion.

The functional anatomy of the pulmonary circulation of the domestic fowl

The architecture of the pulmonary circulation in the domestic fowl was studied in 30 birds of different breeds by injection techniques and serial sections. The branches of the cranial, caudomedial and caudolateral rami of the pulmonary artery form interparabronchial arteries which are essentially transverse to the long axis of the parabronchi. At the periphery of the parabronchus they give rise to intraparabronchial arterioles which form capillaries in the exchange tissue. Most of the capillaries drain into atrial veins via intraparabronchial venules. The atrial veins lie near the parabronchial lumen below the interatrial septa. Some of the capillaries empty into septal venules which form a network underneath the atrial muscles and empty into the atrial veins. The atrial veins draining any particular region converge into a single intraparabronchial vein which penetrates the exchange tissue radially to join an interparabronchial vein. The interparabronchial veins contribute to the cranial and caudal radices of the pulmonary vein. The anatomical pathways of blood and gas indicate a cross-current relationship between pulmonary arterial blood and bulk parabronchial gas flow, and a counter-current relationship between capillary blood and eas in the air capillaries.

Pathogenesis of the Lesions Caused by Cyathostoma bronchialis in the Respiratory Tract of Geese

Cyathostoma bronchialis causes bronchitis of the tertiary, secondary, and primary bronchi during its development in geese. Extreme hyperplasia of the epithelium of the primary bronchi is the foremost lesion seen during prepatency. During patency, generalized pneumonitis in response to aspirated nematode eggs is the most prominent lession, and is accompanied by bronchitis of the primary bronchi and air sacculitis. Fernando, Hoover, and Ogungbade (1973) described the development and migration of Cyathostoma bronchialis (Muehlig, 1884) Chapin, 1925, in geese. In the present paper the pathogenesis of the pulmonary lesions during the migration and patency of C. bronchialis is described, and compared to that of Syngamus trachea in gallinaceous birds. MATERIALS AND METHODS Twoto 4-week-old domestic geese (Anser cygnoides) were fed naturally infected earth worms, as described previously (Fernando et al., 1973), and killed daily from 2 to 6 days and at 8, 10, 12, 14, 15, 17, 21, and 28 days after infection. At least 2 infected geese were killed each day except on day 28, when only 1 bird was killed. One uninfected control was killed each day up to 10 days postinfection. Worms were recovered from 1 lung by the Baermann technique up to 5 days postinfection and from the trachea thereafter. From all birds, 1 lung, with trachea attached, was fixed in 10% formalin. Hematoxylin and eosin-stained 5-/um paraffin sections of these tissues were examined to evaluate the lesions caused by C. bronchialis at the different periods after infection. Received for publication 16 April 1973. * Data for the goose killed at 28 days postinfection was from a thesis presented by S. G. Ogungbade to the University of Guelph in partial fulfillment of the M.Sc. degree. t Department of Pathology. $ Department of Clinical Studies. RESULTS As the number of infective larvae given each goose was unknown, the number of worms recovered postmortem was assumed to be the approximate number causing the lesions reported below. The numbers of worms recovered per goose are given in Table I. We did not find any lesions prior to day 3 postinfection. 3 to 4 days postinfection Worms were seen in parabronchi (Fig. 1) and secondary bronchi close to the lung surface, but by day 4 there were more in the secondary bronchi. The worms almost occluded the parabronchi they occupied. A number of pulmonary lobules had obvious lesions. The interlobular arteries adjacent to these lobules were cuffed by lymphoid cells. The air capillaries of these lobules were obscured by lymphoid hyperplasia (Fig. 2). These lesions were more extensive at 4 days postinfection, and the affected areas were usually close to the lung surface. 5 to 6 days postinfection Worms were found in the primary bronchi. The lymphoid hyperplasia of the air capillaries was less obvious than at 3 and 4 days. Many parabronchi and secondary bronchi were cuffed by lymphoid tissue. The lamina proprial vessels of the secondary bronchi were FIGURES 1-4. Cyathostoma bronchialis in goose lung. H and E. Days postinfection in parentheses. 1. Larva distending parabronchus (3d). X 400. 2. Lymphoid hyperplasia obscuring air capillaries between interlobular artery and neighboring parabronchus. Note ganglion (arrow), between artery and parabronchus, a prominent feature of goose lungs (4d). X 400. 3. Leukocyte infiltration of lamina propria and epithelium of a secondary bronchus (6d). X 400. 4. Hyperplasia of epithelium of a primary bronchus showing many mitotic figures (arrow) (6d). X 400.

Structure of avian lungs

Injection casts of the lung air sac system of 155 species of 47 families of birds were studied, together with preparations of fixed specimens of 45 species. Besides measurements of the fractional distribution of the volumes of the lung and the air sacs, the exchange surface of the air capillaries was determined in 8 species. The avian lung is firmly attached to the thoracic wall and remains constant in volume during both phases of respiration. The primary bronchus enters the lung, giving off at the hilus 4 ventrobronchi and, posteriorly, 7 to 10 dorsobronchi besides some laterobronchi, before it enters the abdominal air sac. The posterior thoracic air sac is connected to one large laterobronchus. These posterior air sacs act as bellows ventilating the lung, much more than the anterior air sacs which are connected to single ventrobronchi. The special manner of the origin of the ventro-, dorso- and latero-bronchi from the primary bronchus is responsible for the ventilation of the parabronchi which connect the total internal surfaces of the dorsobronchi and ventrobronchi. This structure is the “paleopuimo”, found in all birds. Systematically higher birds possess an additional connecting network of parabronchi between the primary bronchus and the posterior air sacs. This “neopuimo ” is best developed in fowllike birds and song birds. The tissue mantle of the parabronchi is made up of a meshwork of blood and air capillaries within which the gas exchange takes place. Development of small air capillaries requires a constant lung volume. The effective exchange surface per volume unit is ten times larger than that of comparable mammalian lungs.

Measurements of capillary dimensions and blood volume in rapidly frozen lungs.

Measurements of capillary dimensions and blood volume in rapidly frozen lungs.

An osmiophilic bilaminar lining film at the respiratory surfaces of avian lungs.

The ultrastructure of the lungs of an adult pigeon, sparrow and hen, and of foetal chickens and chicks of different ages were studied. The presence of a noncellular continuous film on the air capillary surfaces, i.e. on the effective respiratory surfaces, was established at all stages of development as well as in three observed avian species. This film was bilaminar, of a thickness of approximately 100–150 A. The upper and lower layers are strongly osmiophilic, the intermediate layer is of low electron density. This membrane is lacking in all respiratory passages with the exception, mentioned above, of air capillaries. The lung tissue was examined by the periodic acid-silver methenamine technique for the demonstration of polysaccharides and by the colloidal iron method (Mowry's modification of Hale's method) for the detection of acid mucopolysaccharides. After the first mentioned reaction, the picture corresponding to the visualization of “carbohydrate-rich cell coat” (Rambourg, 1967) was obtained. The reaction with colloidal iron was strongly positive at the air capillary surfaces. Nevertheless, the weakly expressed positive reaction was also present at the endothelial cell surfaces. It was assumed that the bilaminar osmiophilic lining film did not contain polysaccharides. Furthermore, this film was also shown to be present in the chicken's lung which had been rinsed several times with saline before fixation. It seems that this layer is secreted by the air capillary epithelial cells. We consider the type of secretion to be merocrine. In view of its behaviour in response to certain histochemical techniques and on the basis of electron microscope investigation its lipoproteinous nature is most probable.

The influence of age and environmental factors on the behaviour of reaggregated embryonic lung cells in culture

1. 1. The developmental histology of the avian embryonic lung has been briefly described; the lung rudiment progresses from a simple structure of epithelial tubes imbedded in mesenchyme at 7 days of age, to a complicated network of tubes, interlacing air capillaries, blood vessels and smooth muscle at 18 days. 2. 2. Embryonic lungs aged 7 to 18 days have been dissociated and reaggregated in a reproducible manner; reaggregation is excellent from 7 to 12 days, but progressively declines with advancing age. The optimum period for complex histotypical reorganization within reaggregates is from 11 to 12 days. Before this time, reorganization is relatively simple while the ability of cells older than 12 days to reconstruct typical structures progressively declines. 3. 3. Isolated pure epithelial cells from 12-day lung fail to reorganize typical structures during 48 hr in culture, but have their full histogenetic capacity when mixed with an optimal proportion of mesenchymal cells at the time of culture. These observations stress the importance of epithelial-mesenchymal interactions in histogenesis, which are thought to be examples of complex histological self-organization rather than of inductive interactions. 4. 4. Pure epithelial cells in culture retain their competency to react with mesenchymal cells for periods of up to 19 hr. This indicates that under the conditions of culture there is no temporal alteration in the capabilities of these cells to interact. 5. 5. Biochemical studies of freshly dissociated 12-day lung cells show that glycolytic enzyme systems are unimpared. About one-third of the cytoplasmic RNA is extracted by the dissociation process, but is resynthesized in culture within 24 hr. 6. 6. The implications of these observations in terms of reconstructive histogenesis in culture has been discussed.