Bone Tissue and Cells
Bone tissue is a specialised type of connective tissue that forms the skeletal system in vertebrates, providing structural support, protection for internal organs, and acting as a reservoir for calcium and phosphate. Bone tissue is composed of cells embedded in a mineralised extracellular matrix.
Cells of Bone Tissue
The sources mention three main types of bone cells: osteoblasts, osteocytes, and osteoclasts.
Osteoblasts
- Origin: Osteoblasts originate from osteoprogenitor cells, which are derived from mesenchymal stem cells.
- Location: Osteoblasts are found on the surfaces of bone matrix, often arranged in a layer resembling simple epithelium.
- Morphology:
- When actively producing matrix, osteoblasts have a cuboidal to columnar shape with basophilic cytoplasm.
- When inactive, they flatten and become less basophilic.
- Function:
- Osteoblasts synthesise and secrete the organic components of the bone matrix, including type I collagen fibres, proteoglycans, and various glycoproteins.
- They also play a crucial role in the mineralisation of the matrix.
Osteocytes
- Origin: Osteocytes are derived from osteoblasts that become trapped within the bone matrix.
- Location: Osteocytes reside in spaces called lacunae within the mineralised bone matrix.
- Morphology:
- Osteocytes are generally smaller and flatter than osteoblasts, with a more almond-shaped cell body.
- They possess long, branching cytoplasmic processes that extend through narrow canaliculi within the matrix.
- Function:
- Osteocytes are less active in matrix synthesis than osteoblasts, but they play a critical role in maintaining the bone matrix and its mineral content.
- The network of osteocytes and their processes acts as a sensor for mechanical stresses on bone, helping to regulate bone remodelling in response to mechanical stimuli.