collagen
Meaning of collagen: Swallowed collagen is broken down into amino acids like any other protein, so it does not arrive intact at skin or joints.
Definition of collagen
Collagen is a fibrous protein that forms the main structural scaffold of connective tissue. Three protein chains wind around one another into a rope-like triple helix, and those ropes bundle into fibrils strong enough to resist pulling. Collagen accounts for roughly a third of all protein in the body and is the bulk of skin, tendon, ligament, cartilage, bone and vessel wall.
Are there different kinds?
More than two dozen types have been described, each assembled from a slightly different combination of chains and suited to the mechanical job of its tissue.
| Type | Where it dominates | What it provides |
|---|---|---|
| I | Skin, bone, tendon, ligament | The most abundant type; resists stretching |
| II | Cartilage and the discs of the spine | Traps water, giving cushioning under compression |
| III | Blood vessel walls, gut, early wound healing | Fine, pliable fibers in stretchy tissue |
| IV | Basement membranes under linings | Forms a sheet rather than a rope, acting as a filter |
How is it built, and what interferes?
Fibroblasts, and their equivalents in bone and cartilage, assemble the chains inside the cell and export them for cross-linking outside it. That construction has one famous dependency: vitamin C is required for the enzymes that modify proline and lysine so the helix can lock together. Without it the helix is unstable, which is the whole of scurvy, appearing as bleeding gums, poor wound healing and fragile vessels. Aging, ultraviolet light and smoking all degrade existing fibers faster than they are replaced, which is why sun-exposed skin thins and creases first.
What happens when collagen is faulty?
Because the same protein appears throughout connective tissue, an inherited fault shows up in several organs at once. Osteogenesis imperfecta involves type I and produces bones that fracture easily along with thin, blue-tinted whites of the eyes. The Ehlers-Danlos group affects several types, giving overly stretchy skin, hypermobile joints and, in one form, fragile arteries. Alport syndrome disturbs type IV and affects the kidney filter, the inner ear and the eye together. This shared origin is why an apparently skin-limited problem may be investigated as a wider collagen disease.
Used in a sentence
The dermatologic evaluation considered whether the skin findings might reflect an underlying disorder of collagen.
Good to know
Inherited disorders of collagen production or structure often affect several connective tissues at once, including skin, joints, blood vessels and the eye, reflecting how widely collagen is distributed rather than being confined to a single organ.
Word origin
Where “collagen” comes from
Formed from Greek kolla, meaning glue, combined with -gen, meaning producing, reflecting collagen's early use in the production of animal glue.