Endosteum
A thin cellular layer lining the medullary cavity, the trabeculae of spongy bone and the central and perforating canals. It contains osteoprogenitor cells, osteoblasts, bone-lining cells and osteoclasts.
Overview
The endosteum is a delicate, often single-cell-thick membrane of flattened bone-lining cells with a little connective tissue. It covers every internal bone surface: the inner wall of the medullary cavity, the surfaces of trabeculae and the lining of Haversian and Volkmann canals. Because these internal surfaces have a far larger area than the external surface, most remodelling occurs at endosteal surfaces.
Quiescent lining cells retract to expose bone when remodelling is activated, and endosteal osteoclasts enlarge the medullary cavity during growth while periosteal osteoblasts add bone outside. With ageing, endosteal resorption exceeds periosteal apposition so the cortex thins and the marrow cavity widens ("trabecularisation" of the cortex). The endosteum also forms part of the haematopoietic stem-cell niche and contributes internal callus during fracture healing.
- Location
Lines the medullary cavity, trabeculae, central (Haversian) and perforating canals.
Anatomy
- Histology
Flattened bone-lining cells and osteoprogenitor cells; active osteoblasts are cuboidal; osteoclasts sit in Howship lacunae.
Function
- Bone remodelling at internal surfaces
- Enlarges the medullary cavity during growth
- Internal callus formation after fracture
- Contributes to the haematopoietic stem-cell niche
Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.