Three-dimensional architecture of elastin and collagen fiber networks in the human and rat lung

Abstract

Collagen and elastin fibers are the major components of the lung connective tissue, but their spatial organization has not been well documented. We have demonstrated the three-dimensional architecture of collagen and elastin fiber networks in the human and rat lung using scanning electron microscopy. These networks in their original forms were extracted by an alkali-water maceration technique and a formic acid treatment, respectively. The collagen fibers formed a continuum extending throughout the lung and pleura. They were condensed in the alveolar mouth and subdivided into smaller fibers in the alveolar septa, thus forming basket-like networks. Sizes of the alveolar pores in the collagen fiber network of the alveolar septa became larger with age. In the collapsed lung, collagen fibers in the alveolar mouths and septa took on wavelike configurations, while in the inflated lung they became straight. The elastin fibers also formed a continuum, rich in the alveolar mouths and poor in the alveolar septa, were quite straight without any wavelike configuration. Transmission electron microscopy showed that collagen and elastin fibers were intermingled, suggesting that both fiber systems may act as parallel mechanical elements to stress or strain applied. Our results suggest that at low levels of strain the wavy collagen fibers are easily extended to allow alveolar mouths and alveoli to expand, with most of the stress being borne by adjacent elastin fibers, while at higher levels collagen fibers become straight and limit any further distension of alveolar ducts and alveoli. The elastin fiber continuum appears to permit the lung to effectively recoil or retract. The present study has also shown that alveolar pores enlarge with age, suggesting that collagen remodeling may be related to the pathogenesis of emphysema.

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

“…Collagen and elastic tissue fibers, proteoglycans, and other glycoproteins are the main structural macromolecules of the connective tissue elements of mammalian lung (Hance & Crystal, 1975;Hopkins et al 1986;Crouch et al 1997;Tochima et al 2004). More recent studies report that collagen fibers fail at strains between 6 and 22% (Liao & Belkoff, 1999).…”

“…Arising from the need to exploit and integrate their distinctly different mechanical properties, in animal tissues, elastic tissue fibers are almost constantly found in close topographical relationship to the collagenous fibers (Elden, 1968;Gosline, 1976;Gosline & French, 1979;Alter, 2004). In the compliant mammalian lung, elastic tissue occurs abundantly and diffusely (Gonçalves et al 1995;Tochima et al 2004). Carton et al (1964) observed that more elastic tissue was present in the lungs of two mammalian species than was theoretically expected.…”

“…the area containing the air and the blood capillaries, is literally 'suspended' between the axial (A) and peripheral (E) pillars by a dense network of collagen fibers. Gonçalves et al 1995;Maina, 2002;Tochima et al 2004). The corresponding structures of the avian lung have not been investigated in detail.…”

“…Tissues samples measuring about 2 · 3 · 5 mm were taken from the lung and digested to remove all tissue components except collagen according to the methods described by Ohtani (1987Ohtani ( , 1992 and Tochima et al (2004). Briefly, the tissues were placed in a 10 M solution of sodium hydroxide (NaOH) for 4 days at room temperature (20°C).…”

The elastic fibre network of the human lumbar anulus fibrosus: architecture, mechanical function and potential role in the progression of intervertebral disc degeneration

“…A reduction in the tensile strength of these tendons was also observed. In the mature human lung, elastin constitutes approximately 30% of the dry tissue weight [9]; elastic elements form a complex, three-dimensional fibrous network, interwoven with collagenous elements, and there is evidence of mechanical connections between the two [65]. In a guinea pig model, the effect of enzymatically removing elastin on the quasi-static mechanical properties of lung parenchymal strips was to cause a large reduction in initial modulus and an increase in extensibility [75].…”