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Osteoclast
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The osteoclast is the cell whose job is to break bone down. It does not come from bone: it comes from the bone marrow, from the same hematopoietic lineage that produces blood cells. And it is no ordinary cell, because it is born from the fusion of several precursors, so it ends up with several nuclei inside. That is why it is called multinucleated.
To do its work it attaches to the surface of the bone. There it releases two tools: lysosomal enzymes, proteins that cut through organic material, and hydrogen ions, which is to say acid. With them it breaks down the bone matrix, which has two parts: the calcium phosphate crystals, the hard mineral part, and the collagen, the fibrous part.
Breaking bone down is not destruction for its own sake: it is the first half of a cycle called bone remodeling. The osteoclast removes the old or damaged bone and leaves a hole behind; then the osteoblast arrives and fills it with new collagen and mineral. It works like the demolition crew that clears the space another crew will build in.
In brief
The osteoclast is the cell that resorbs bone; it arises from a hematopoietic lineage in the bone marrow and is multinucleated because it forms by fusing precursors.
It attaches to the bone surface and dissolves the matrix with lysosomal enzymes and hydrogen ions, attacking the calcium phosphate crystals and the collagen.
It is half of bone remodeling: it removes old or damaged bone, and the osteoblast fills the pit with new collagen and mineral.
It works like the demolition crew that clears the space another crew will build in.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Bone Remodeling, StatPearlsPublished
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