Research Article

Three-Dimensional Structure and Disposition of the Air Conducting and Gas Exchange Conduits of the Avian Lung: The Domestic Duck (Cairina moschata)

Figure 6

Scanning electron micrographs showing the three-dimensional architecture of the smaller air conduits and gas exchanging units. (a) and (b): Scanning electron micrographs of mercox casts (intratracheal infusion) showing the parabronchi (PB) with numerous infundibulae (arrowheads in (a), IF in (b)), some of which are raptured (arrowheads in (a)) due to presence of trapped air. Dark arrowheads in (b) denote globular air capillaries. (c) and (d): Micrographs of critical point-dried tissue showing a longitudinal view of the exchange units and a bird’s eye view (d) of the same. The atria are shallow but the infundibulae are long (white arrows in (c)) and give rise to numerous air capillaries (arrowheads in (c)). The atria are surrounded by a ridge of epithelial tissue (dark arrows), which is reinforced by smooth muscle characteristic of interatrial septa (see also Figure 7). Some air capillaries emerge directly from the floor of the atrium (white arrowheads in (d)) while others (white arrows in (d)) are extensions from infundibulae (IF).
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(c)
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(d)