Chondrocyte

Cartilage has only one cell type of its own, and it is called the chondrocyte. It lives tucked into its lacuna, the hollow left for it inside the tissue, and from there it does the two things that matter: it produces the cartilage matrix, the firm material around it, and it maintains that matrix, meaning it repairs and renews it as it wears down.

What comes out of it is building material. It makes collagen, the fiber that provides strength, and the extracellular matrix, which is everything filling the space outside the cells; that is what keeps the cartilage of the joints intact and lets it pull off something uncommon, being firm and flexible at the same time. And it lives wrapped in those same collagen fibers it produced. If the tissue is injured, the chondrocyte is what responds: this is called chondral repair, which means repair of cartilage.

It does all of this under harsh conditions. Articular cartilage has very few blood capillaries, so very little oxygen reaches the chondrocyte and it works at low oxygen tension. Its solution is to switch engines: the chondrocyte of hyaline cartilage metabolizes glucose by anaerobic glycolysis, that is, burning sugar without oxygen.