Composed are types I, II, III, V of many bundled fibrils;
Type IV is not, you’ll find it in the lenses of your eyeballs.
With cross-links and a triple-helix structure as foundation,
Resilience and great tensile strength resist in deformation.
The matrix of some structures, such as those which are elastic,
Contains elastin, too, which is both yellow and fantastic.
Elastin’s charact’ristic is a stretch in two dimensions;
It will recoil when force applied refrains its course of tension.
But I digress – it’s collagen, that glycoprotein staple,
That is to be the topic of this truthful little fable.
Arranged within ground substance, they indeed go hand in hand;
Proportions of components, each, reflect tissue’s demand.
The skin, the stretchy arteries, and rigid, rugged bones,
Exemplify how ratios therewithin sport different tones.
As well, the cross-link density gives qualities, diverse,
(And genes inform their numbers, so there’s no need to rehearse.)
Said cross-links come in bundles, which are random in the skin,
And sheet-like in the vessels, though those really are quite thin.
In tendons, they are parallel, so neatly they’re aligned,
This anchors muscles, which contract; their range thus is defined.
Stability, perhaps, is both its downfall and its boon,
For turnover does not occur, and won’t, anytime soon.
The consequence is that, when damage happens to these tissues,
The cross-links, once so strong, go all awry, and cause some issues.
The collagen that’s been messed-up will, in due time, degrade,
And under good conditions, be remodel’d and remade.
The fibrils will reorganize; most should attempt repair,
And properly directed force should be applied, with care.
Dynamic are the tissues that connect us through and through;
Foremost, know “form is function” — it’s what collagen knows, too.