A cell walled in by its own secretions, housed in a lens-shaped chamber called a lacuna
Osteocyte — the trapped former osteoblast.
Anatomy · Cells & tissues
Osteocyte
The commonest cell in mature bone
Bone tissue · trapped in the matrix
The mature bone cell: an osteoblast that has become entombed in the hard matrix it made. Each osteocyte sits in a small cavity, a lacuna, and reaches out through hair-thin channels, the canaliculi, to touch its neighbours and the blood supply in the central canal of its osteon. This network senses mechanical strain and damage, and sends signals that tell osteoblasts and osteoclasts where to add or remove bone. Osteocytes are by far the most numerous bone cells and can live for decades.
How to spot them
- ▸Small dark, spidery cells in lens-shaped holes (lacunae) between the concentric layers of an osteon
- ▸Fine radiating channels, canaliculi, linking the lacunae like the spokes of a wheel
- ▸In a ground-bone section the lacunae and canaliculi show up as dark spots and lines around a central canal
- ▸Arranged in rings around the Haversian canal, which carries a vessel and nerve
- ▸Much smaller and more shrunken than the surface osteoblasts that made them
What to know
Thin channels called canaliculi carry its dendrite-like processes to neighbours and to the central canal
Osteocyte — the lacunar–canalicular network.
It makes up around 90–95% of the cells in an adult skeleton
Osteocyte — the most abundant bone cell.
It secretes sclerostin, which restrains bone-building osteoblasts
Osteocyte — sclerostin blocks Wnt signalling; antibody drugs to it are used against osteoporosis.
It senses the strain of walking and weightlifting, and tells the skeleton where to strengthen: the cellular basis of Wolff's law
Osteocyte — mechanosensing.
Rings of these cells around a Haversian canal make up the microscopic unit of compact bone
Osteocyte — they lie in lacunae between the lamellae of an osteon.
It produces the hormone FGF23, which lowers phosphate in the blood
Osteocyte — bone acts as an endocrine organ.
Key ideas
- Osteocytes act as strain gauges: fluid moving through the canaliculi when bone bends is detected by the cells, which then control the balance between bone formation and resorption.
- Their long survival relies on their canalicular link to the blood supply; if a region of bone is deprived of blood, the osteocytes die and the bone is lost.
Quick-fire facts
- •Each starts as an osteoblast; roughly 10–20% of osteoblasts end up buried as osteocytes
- •They lack mitotic activity and cannot divide once formed
- •Osteocytes are linked by gap junctions between their processes, forming a communication network throughout the bone
- •A lacuna houses the cell body; a canaliculus houses each process
- •They release RANKL, which drives osteoclast formation, and sclerostin, which brakes osteoblasts
- •Osteoblasts, osteoclasts and osteogenic cells lie at the bone surface; only osteocytes lie deep inside
- •Volkmann's canals run across the bone linking the central canals of neighbouring osteons
- •Osteocyte death after blood supply is lost (avascular necrosis) can collapse the head of the femur
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