DISTRIBUTION OF ELASTIC SYSTEM FIBERS IN HUMAN FETAL LIVER

Elastic system fibres are extracellular matrix components found in dif ferent organs for which they provide elasticity and some mechanical re sistance. Oxytalan, elaunin and elastic fibres, which possess graduate d amounts of elastin, are the 3 forms of elastic system fibres that ar e identifiable by their tinctorial and ultrastructural features. The d istribution of these fibres in adult human liver is well-established b ut little, if anything, is known about them in fetal liver. The distri bution of elastic system fibres was therefore investigated in human fe tal liver, and the process of elastogenesis characterised. Specimens o f liver from 24 human fetuses ranging in age from 13 to 38 wk postfert ilisation were studied. The results are presented in relation to gesta tional age and the size of the portal tracts. Portal tracts exhibited a network of oxytalan fibres at 13 wk; elaunin fibres appeared later a fter 20 wk postfertilisation. Elastogenesis occurred more rapidly in v enous than in arterial walls, and in veins it was more evident in the adventitia. A microfibrillar network of oxytalan fibres was observed a round biliary ducts from the outset of their development. Elastogenesi s follows the sequence oxytalan, elaunin and elastic fibres, but the e lastogenetic process only completes its maturation in arterial walls, thus leading to the internal elastic lamina.