The Organization of Collagen in Growing Tensile Tissues

As a young animal grows, its organs, musculature and skeleton increase in size and the connective tissues must elongate commensurately. This requirement poses a problem: Tensile connective tissues are built from highly ordered collagen and proteoglycan molecules, and if they are to transmit forces over a distance, the components must be connected into polymers. How can the polymers be extended during growth without disrupting the structure or cutting the polymers? The conceptual problem of growth in a tendon, for example, may be compared to the situation of a dinghy anchored in a rising tide. Unless the anchor line is lenghtend, the bot will be dragged below the surface, but if the line is firmly spliced at the boat and the head of the anchor, how does the sailor lengthen the line? It is proposed that the growth process requires repeated stretching just beyond the elastic limit and that entails the strain-catalyzed hydrolysis of intermolecular bonds; however, the bonds can reform in a new location to produce a structure similar to but longer than the original and local synthesis can fill structural voids. In this way, the protein content, continuity and tensile strength of the tissues are not los during growth.