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

Slight volume changes in the duck lung do not imply a fundamental change in the structure of the parenchyma

Slight changes in lung volume have previously been reported in ducks. We studied the functional structure of the lung of the domestic duck using classical anatomical techniques as well as ultrasound monitoring to unravel the causes of such changes. Later dorsal and medioventral secondary bronchi were superficially positioned and covered with a thin transparent and collapsible membrane, internally lined with a cuboidal to squamous epithelium. The lung parenchyma was rigid, with atria well supported by septa containing smooth muscles, interparabronchial septa reinforced by collagen fibres, and blood capillaries supported by epithelial plates. On ultrasound monitoring, an outward and inward movement of the lung surface during inspiration and expiration, respectively, was evident at the region where the airways were covered by the thin membranes. The movements plausibly facilitated air movement in the lung just like the air sacs. We conclude that volume changes in the duck lung occur due to a slight morphological adaptation rather than a change in the archetypical design of the avian lung parenchyma.

Casting materials and their application in research and teaching

From a biological point of view, casting refers to filling of anatomical and/or pathological spaces with extraneous material that reproduces a three-dimensional replica of the space. Casting may be accompanied by additional procedures such as corrosion, in which the soft tissue is digested out, leaving a clean cast, or the material may be mixed with radiopaque substances to allow x-ray photography or micro computed topography (µCT) scanning. Alternatively, clearing of the surrounding soft tissue increases transparency and allows visualization of the casted cavities. Combination of casting with tissue fixation allows anatomical dissection and didactic surgical procedures on the tissue. Casting materials fall into three categories namely, aqueous substances (India ink, Prussian blue ink), pliable materials (gelatins, latex, and silicone rubber), or hard materials (methyl methacrylates, polyurethanes, polyesters, and epoxy resins). Casting has proved invaluable in both teaching and research and many phenomenal biological processes have been discovered through casting. The choice of a particular material depends inter alia on the targeted use and the intended subsequent investigative procedures, such as dissection, microscopy, or µCT. The casting material needs to be pliable where anatomical and surgical manipulations are intended, and capillary-passable for ultrastructural investigations.