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Periosteum
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The periosteum is the membrane that wraps the bone on the outside. It covers almost all of it, with exceptions: where the ligaments and tendons insert, where there is articular cartilage, the smooth surface where one bone meets another, and the sesamoid bones, which have no periosteum.
It is not a simple lining. It has two layers. The outer one is fibrous and tough. The inner one is cellular. And the periosteum contains osteoblasts, the cells that build bone; osteoclasts, the ones that resorb it; and osteoprogenitor cells, which are the reserves. With that crew it takes part in bone growth, in the healing of a fracture and in remodeling, the constant renewal of bone throughout life.
It is also firmly tied down. Sharpey fibers, collagen bundles that come off the periosteum, are driven into the bone matrix like the staples that hold fabric to wood. That is why the covering does not slide over the bone: it is part of it.
In brief
The periosteum is the membrane that covers the outer surface of bone, except at ligament and tendon insertions, beneath articular cartilage and on sesamoid bones, where it is absent.
It has a fibrous outer layer and a cellular inner layer, and it contains osteoblasts, osteoclasts and osteoprogenitor cells, which is why it takes part in growth, fracture healing and remodeling.
Sharpey fibers, collagen bundles from the periosteum, embed in the bone matrix and anchor the periosteum to the bone.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingHistology, Periosteum And Endosteum, StatPearlsPublished
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