Elastic is the name given to some fibres that are widely distributed throughout the body, such as skin, arteries and veins, lung, etc. Generally, they are found where some movement is required from the tissue involved and, as the name implies, they help restore the tissue after movement. They may be increased or decreased in amount due to disease and it may be necessary to demonstrate them for that reason, but their demonstration is quite often used to show that a structure is a blood vessel, since both arteries and veins have a ring of elastic fibre in their wall. Wikipedia has an article on elastic fibres and another on "elastic arteries".
Sometimes the word "elastin" is used for these fibres. Strictly speaking this is incorrect as elastin is the name of a major protein component of elastic. The fibres themselves are referred to as "elastic fibres".
The fibres are resistant to autolysis and are quite easily fixed. Most fixatives preserve them, and standard formalin variants work well. Under ultra-violet light they may have a green to blue-white fluorescence, the colour depending on the particular filters used. The coarser fibres can often be seen in H&E stained sections as a smooth, pale pink material, but fine fibres are much more difficult or impossible to see and for their unequivocal identification selective staining methods are necessary. They are not infrequently seen in sections stained for amyloid with direct cotton dyes, such as congo red and sirius red F3B. This is likely due to both amyloid and elastic fibres being stained via non-polar forces.
Methods for the demonstration of elastic fibres are of several types, listed below. Most of these methods are satisfactory in practice. However, it should be noted that elastic fibres vary in their size and thickness. Large arteries such as the aorta, for instance, may have very coarse fibres of quite thick elastic in the arterial wall, whereas the tissue surrounding the alveoli in the lung may have quite small, fine fibres. This physical difference can affect the choice of methods used to demonstrate the fibres.
There has been an evolution in the explanations for the selectivity of methods for elastic. It used to be explained on the basis of ionic staining, and those methods which overstained were differentiated to remove dye from the less densely stained tissue. Then it was realised that non-polar forces played a part and the explanation was based on hydrogen bonds. It was then shown that the fibres still stained when some dyes not capable of forming hydrogen bonds were used. However, these dyes all had multiple aromatic rings and were all capable of bonding by Van der Waal's forces. That is now the most commonly given explanation, that dyes bind preferentially to elastic fibres due to van der Waal's forces. The explanation appears to be valid for all the types of methods.
Oxytalan & elaunin fibres
Oxytalan fibres are thought to be immature elastic fibres. After oxidation with peracetic acid, performic acid or potassium pemanganate they may be demonstrated by aldehyde fuchsin, but reportedly do not stain with Verhöeff's hematoxylin. They are defined in the MediLexicon dictionary as:
A type of connective tissue fiber representing an early stage in the formation of elastin fibers and found throughout the body, particularly in the periodontal ligament and gingivae.
Elaunin fibres are defined in the same dictionary as:
A component of elastic fibers formed from a deposition of elastin between oxytalan fibers; found in the periodontal ligament and in the connective tissue of the dermis, particularly in association with sweat glands.
Bancroft notes that elaunin fibres may be stained with orcien, aldehyde fuchsin and iron-resorcin-fuchsin, but do not stain with Verhöeff's hematoxylin nor with orcinol-new fuchsin.
Baker, John R., (1958)
Principles of biological microtechnique
Methuen, London, UK.
Bancroft, J.D. and Stevens A. (1982)
Theory and practice of histological techniques, Ed. 2
Churchill Livingstone, Edinburgh & London, UK.
Last updated January 2019