Figure 510

Collagen and elastic fibers. Photomicrograph of a mesentery spread stained with resorcin-fuchsin. The mesentery is very thin, and the microscope can be focused through the entire thickness of the tissue. The delicate thread-like branching strands are the elastic fibers (E), Collagen fibers (C) are also evident. They are much thicker, and although they cross one another, they do not branch. x200.

The elastic property of the elastin molecule is due to its unusual polypeptide backbone that causes random coiling

The random coiling of the elastin molecule allows the elastic fiber to be stretched and then to recoil to its original state. Elastin also contains desmosine and isodesmo-sine, two large amino acids that are responsible for the co-valent bonding of the elastin molecules to one another (Fig. 5.11). With the TEM, elastin appears as an amorphous structure of low electron density. In contrast, the fibrillin microfibrils are electron dense and are readily apparent even within the elastin matrix (Fig. 5.12). In mature fibers, the fibrillin microfibrils are located within the elastic fiber and at its periphery. The presence of microfibrils within the fiber is associated with the growth process; thus, as the fiber is formed and thickens, the microfibrils become entrapped within the newly deposited elastin.

In Marian's syndrome, a complex, autosomal dominant, connective tissue disorder, expression of the fibrillin gene (FBN'l) is abnormal. Immunofluorescence of a skin biopsy specimen from a person with Marian's syndrome will show an absence of elastin-associated fibrillin microfibrils. One of the consequences of the disease is abnormal elastic tissue.

elastin molecules elastin molecules



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