16.0.1 POJA-L7201 LOCOMOTOR SYSTEM: BONE
INTRODUCTION-1: BONE CELLS AND MATRIX
Bone is a particular type of supporting tissue; it is a specialisation of the connective tissue with cellular elements and the supporting extracellular matrix (ECM). Osteoprogenitor cells or osteogenic cells, are stem cells or precursors to the more specialized bone cells (osteocytes and osteoblasts), residing in the bone marrow. Derived from young mesenchymal stromal cells, osteoprogenitor cells turn into spindle cells at the surface of matured bones.
In matured bones they exist as flattened spindle-shaped structures in the periost layer.
INTRODUCTION-1: BONE CELLS AND MATRIX
Bone is a particular type of supporting tissue; it is a specialisation of the connective tissue with cellular elements and the supporting extracellular matrix (ECM). Osteoprogenitor cells or osteogenic cells, are stem cells or precursors to the more specialized bone cells (osteocytes and osteoblasts), residing in the bone marrow. Derived from young mesenchymal stromal cells, osteoprogenitor cells turn into spindle cells at the surface of matured bones.
In matured bones they exist as flattened spindle-shaped structures in the periost layer.
CELLS THAT FORM BONE TISSUE
The following four or five cell types are found associated with bone and its metabolism:
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In the advanced stages the ECM additionally contain calcium phosphate formed in calcium hydroxyapatite crystals. These crystals are found associated with predominantly type I collagen fibres in the matrix that is well organized in multiple thin layers, the so-called lamellae. Traces of types V collagen and in lesser number of types III, XI and XIII collagens also are present. Lamellae grow by apposition.
EXTRACELLULAR MATRIX
The major component of the ECM (extracellular matrix) is formed by collagen fibres embedded in a ground substance consisting of non-collagenous proteins (GAG’s glycosaminoglycans) such as:
The major component of the ECM (extracellular matrix) is formed by collagen fibres embedded in a ground substance consisting of non-collagenous proteins (GAG’s glycosaminoglycans) such as:
- Proteoglycans with their side chains of glycosaminoglycans (e.g., chondroitin sulphate, keratan sulphate, hyaluronan).
- Glycoproteins: Osteonectin, dentin matrix protein (DMP), sialoproteins (osteopontin, aka BSP-1).
- Bone-specific proteins Most abundantly present is vitamin K2-dependent osteocalcin, matrix gamma -carboxyglutamic acid protein (vitamin K-dependent matrix Gla protein or MGP).
- Growth factors and cytokines e.g., bone morphogenic proteins (BMP’s), insulin-like growth factor (IGF’s), tumour necrosis factor- alpha.