Bone and Joint Histology

Authors Avatar by BasilRazi (student)

Bone & Joint Histology


  • It is a specialised connective tissue.
  • Osteogenic cells  osteoblast (makes matrix, active when young, and after fracture)  osteocyte  osteoclast (functions in resorption, breakdown of bone matrix) (makes cavities) (from blood monocyte)

Bone Functions

  • Framework for support of the skeleton
  • Protection: brain, spinal cord, lungs and heart
  • Levers for muscles attached to them via tendons
  • Reservoir for minerals e.g. calcium, magnesium, phosphates etc.

Bone Matrix

  • Components
  • Extracellular matrix (ground substance and fibres) consists of inorganic material (65%) e.g. calcium phosphate, calcium carbonate, magnesium, sodium, potassium, bicarbonate, fluoride, citrate, sulfate, and hydroxide.
  • Minerals give bone hardness and rigidity
  • Organic component (35%) mostly type I collagen (95%)- gives bone slight flexibility; and ground substance e.g. GAGs with proteoglycans, which contain chondroitin and keratin sulfates which give bone resilience
  • Development
  1. Bone starts as osteoid, which is collagen and GAG’s with no minerals
  2. Bone becomes mineralised (immature, primary, or woven bone). It is the first bone to appear in development and in repair after fractures
  3. Bone starts to remodel as the adult form (mature, secondary, lamellar)

Bone Cells

  1. Osteoprogenitor (osteogenic) cells: from embryonic mesenchyme, which differentiate into osteoblasts. Found in inner cellular layer of the periosteum, lining Haversian canals, in the endosteum (lining medullary cavity)
  2. Osteoblasts: derived from osteoprogenitor cells, form and grow new bone by synthesis of organic components of bone matrix. Found on the surfaces of existing bone tissue where they deposit new bone matrix (osteoid) which contains no minerals. Later mineralization occurs, tissue is new bone. Osteoblasts extend processes with neighbouring osteoblasts for molecular transport. Sit on the edge of bone.
  3. Osteocytes: flat cells with small cytoplasmic processes. Aid in the maintenance of bone tissue and storage of minerals. Each osteoblast becomes surrounded by secreted matrix, once this occurs, the cell is known as an osteocyte (mature bone cell), and the space it occupies is a lacuna. Radiating out in all directions from the lacuna are tunnel-like spaces (canaliculi) which house the cytoplasmic processes of the osteocytes. The canaliculi allow transfer of nutrients, wastes between the osteocytes and blood. They are very active cells. Communicate via cytoplasmic processes in the canaliculi, metabolic communication.
  4. Osteoclasts: large motile, multinucleated cells (150 um diameter) which contain up to 50 nuclei. These cells break up and resorb bone. Osteoclasts occupy shallow depressions (Howship’s lacunae). The ruffled border (infolded plasma membrane) is that part of the cell that is directly involved in the resorption of bone. It removes bone enzymatically, mineral deficiencies then the osteoclasts become active to release the minerals that have been stored in bone, hence the person becomes fracture prone. The multinuclear nature of the osteoclasts is a good identifying factor
Join now!

Periosteum and Endosteum

  • Vascular, fibrous layer surrounds bone except over articular surfaces.
  • 2 layers
  • Outer layer is collagen with some elastic fibres. This layer distributes vascular and nerve supply to bone.
  • Inner layer is cellular (osteogenic layer, osteoprogenitor cells), gives rise to new bone.
  • Central cavity of bone is lined with endosteum- thin CT composed of osteoprogenitor cells and osteoblasts.
  • From the outer layer of periosteum, fine bundles of collagenous fibres (Sharpey’s) penetrate the underlying bone at intervals to attach the periosteum, especially at the sites of attachment of tendons and ligaments.
  • ...

This is a preview of the whole essay