Study of the elastic fibres' framework of the rat lung

A combination of intravascular resin injection and formic acid incubation was used to study the three-dimensional organization of the elastic fibres of the adult rat lung by scanning electron microscopy (SEM). After SEM observations, the same samples were further processed for transmission electron microscopy (TEM) in order to confirm the presence of the elastic fibres and to complement some aspects of its surface morphology observed under the SEM. Complementary studies by light microscopy (LM) and TEM using specific histochemical methods for the elastic fibres were also performed. The SEM study clearly demonstrated that the cast of the microvasculature acted as a scaffold to preserve the in vivo arrangement of the easily collapsible elastic tissue. The methodology used allowed the observation of a fine framework of elastic fibres representing remnants of the alveolar walls in close association with the capillaries interwoven with the network of elastin. Each thick elastic fibre was composed of a bundle of thin fibres. Some of these thin fibres separated from the main fibre, join other fibres, giving the appearance of an anastomosing net. The interwoven network of elastin and its proximity with the capillaries suggests that the distensibility of the alveolar wall should contribute to the subtle rhythmical change of the alveolar microcirculation at each respiratory movement. On the sub-pleural region of the lung, the elastic fibres were observed forming a continuous and fine mesh network. The elastic fibres linking the walls of the intrapulmonary conducting airways, the vessels wall and the alveolar and sub-pleural elastic network establish an interrelated and interlaced continuous framework, certainly with great physiological implications to the overall process of the mechanics of the lung respiratory function. The methodology applied was a useful tool in order to study the spatial organization of the pulmonary elastic fibres, its branching and close relation with the other lung structures.