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

Abstract

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.

Three‐Dimensional Serial Section Computer Reconstruction of the Arrangement of the Structural Components of the Parabronchus of the Ostrich, Struthio Camelus Lung

“…The existence of a crosscurrent arrangement of the structural components has been reported previously by Duncker (1971Duncker ( , 1974Duncker ( , 1979, Abdalla and King (1975), West et al (1977), Maina (1982Maina ( , 1988, and (Abdalla, 1989). But, while these studies were meticulously done, the techniques that were applied were not sufficiently robust to categorically explicate the highly complex spatial architecture of the exchange tissue of the avian lung.…”

“…The structure and the arrangement of the air-and the blood-conducting components in the parabronchus of the Ostrich lung, especially concerning lack of interparabronchial septa and presence of shallow atria and poorly developed atria muscles, resembles some of those reported in the lungs of the many bird species studied by Duncker (1974), the Khaki Campell Duck (Anas platyrhynchos) and the Homing Pigeon (Columba livia) investigated by West et al (1977) and the Domestic Fowl (Gallus gallus variant domesticus) examined by Abdalla and King (1975), Brackenbury and Akester (1978), Fujii et al (1981), and Maina (1982Maina ( , 1988. Maina et al (1982) observed that the atria, interatrial septa, and atrial muscles are poorly developed in the relatively smaller and more metabolically active passeriform, columbiform, cuculiform, and psittaciform taxa of birds but well-formed in the galliforms, anseriforms, and charadriiforms.…”

“…This assertion has so far not been supported by experimental evidence. West et al (1977) made a cursory mention of BCs that originated directly from the IPAs but no image/illustration of this atypical feature was given to convince or help the reader assess its authenticity. Moreover, it was not stated as to which of the lungs of the two species that they examined, namely the Khaki Campbell Duck and the Homing Pigeon, it occurred.…”

“…Study of histological sections, as performed by Abdalla and King (1975), does not allow direct rendition to the three-dimensional (3D) arrangement: the 3D schemes that are developed pursuant to such studies depend largely on the intuition and judgment of the investigator and may be subject to personal bias. Regarding the casting method that was used by West et al (1977), Maina (1982Maina ( , 1988, and Nasu (2005), the accuracy depends on the suitability and the nature of the material used for injection in relation to the size of the structures that are cast. Artifacts may arise from underfilling, overfilling, or in extreme cases extravasation of the material, after failure of the wall of the conduit (Murakami, 1971;Clark et al, 1979;Ohtani, 1980;Lametschwandtner et al, 1984).…”

Implicit mechanistic role of the collagen, smooth muscle, and elastic tissue components in strengthening the air and blood capillaries of the avian lung

“…The elastic tissue fibers may act as energy-storing elements in opposition to the intrinsic tone of the smooth muscle fibers, and the collagen fibers may limit the stretchability of the contractile components. McLelland (1989) described the orientation of the atrial septa as that of a 'shallow-pitched helix, and King & Cowie (1969), Gerisch &Schwartz (1972), andWest et al (1977) observed that the larger atrial muscles form an angle of 60-70°, whereas the smaller ones form an angle of 45°to the long axis of the parabronchus; the strut-like oriented atrial muscles may provide linear stiffening and efficient dissipation of Contraction of the atrial smooth muscles exerts a pulling force directed towards the center of the parabronchial lumen (the arrows of the springs projecting into the parabronchial lumen). The pull is transmitted to the elastic fibers (shown by the springs) in the interatrial and the interinfundibula septae.…”