Overview elastic fibres (Fibrae
Pages with explanations are linked to the
text below the images if available! (Labelling is in German)
Elastic fibres (Terminologia anatomica: Fibrae elasticae) are extracellular
tissue fibres that can reversibly be stretched up
to twice their original length. They consist of a central amorphous
hardly electron-dense substance called
histologica: Elastinum) that often appears blurred in sections.
It is surrounded and partly infiltrated by tiny very electron-dense fibrillin
fibrils (Terminologia histologica: Fibrillae fibrillini).
These extracellular microfilaments have diameters of 6 to 8 nm
and serve for anchoring the elastic fibres to surrounding tissues. Fibrillin
alone (without elastin) is encountered in the zonular fibres between the
ciliar body and the capsule of the eye lens.
Such fibrillin bundles totally lacking elastin are called oxytalan
fibres (Terminologia histologica: Fibrae
oxytalanae) and are very rare. Another kind of rare fibres called elaunin
fibres (Terminologia histologica: Fibrae elauninae) consist of fibrillin
bundles with sparsely aggregated elastin. The amorphous elastin
biochemically is similar to collagen and
is rich in glycine and proline. It further contains some hydroyxproline
but lacks hydroxylysine which in collagen
is responsible for the aggregation in form of tropocollagen. Apart from
valin only desmosin and isodesmosin are interlinking the polypeptid chains
in elastin. In contrast to collagen fibrils
polypeptid chains are singly cross-linked in elastin and arrange increasingly
parallel when stretched. When stretching is over they draw back the macromolecules
into the original aggangement which is the basis for the elastic character
of elastic fibres. The stronger the lengthening effect of an elastic fibre
is the more power is necessary for further stretching.
|Aorta: Tunica media with
elastic fibre network (monkey)
|membrana elastica interna
of an arteriole (rat)
human umbilical artery
|large elastic fibre bordered by
collagen fibres of human subcutis
Elastin is synthetised and released into the extracellular matrix
in form of proelastin by fibroblasts and smooth
muscle cells. It then is cross-linked by enzymes of the extracellular
space. Elastic fibres are very stable and long-lasting. They even are
insoluble in boiling water. Further they are quite resitant to acids ond
bases. Degenerative changes such as deposition of calcium salts will result
in reduced elasticity in older age.
Elastic fibres appear shiny in light microscopy by their strong
light-diffraction and require special
stains such as resorcin-fuchsin to become homogenously blackly stained.
Non-stretched fibres appear isotrop
in polarised light. With increase of lengthening peptid molecule arragement
gets more and more parallel resulting in a stetch-anisotropy.
The thickness of the fibres ranges from some hundret nanometers
to 4 µm. Elastic fibres often form
meshworks and they condense as elastic membranes in the walls of
and arteries: Membrana elastica interna
and -externa. Elastic fibres are present in loose and fibrous connective
tissue, in the stroma of
organs (e.g. in the lung) and in capsules of
organs. Connective tissue appears slightly yellow
when it has a high content of elastic fibres e.g., Ligamenta
flava, aorta, elastic
cartilage). A high content of elastic fibres is also seen in the vocal
cords and the wall of the gut.
--> reticular fibres, collagen
fibres, fibroblasts, connective
tissue, ground substance
--> Electron microscopic atlas Overview
--> Homepage of the workshop
Two images were kindly provided by Prof. H. Wartenberg;
other images, page & copyright H. Jastrow.