Cellular Composition of the Periosteum
The periosteum is not merely a mechanical sheath, but a biologically active zone. It contains cells that ensure the continuous renewal of the bone matrix:
- Osteoblasts — cells that synthesize the bone extracellular matrix.
- Osteoclasts — multinucleated cells that resorb old or damaged bone tissue.
- Osteogenic cells — cambium (stem) elements. They possess a high differentiation potential and play a critical role in regenerative processes, especially during fracture healing.
Effect of Oxygen on Regeneration
The fate of periosteal osteogenic cells depends directly on their microenvironment, primarily the partial pressure of oxygen ($O_2$). This mechanism is of fundamental importance in fracture healing:
- At low $O_2$ levels: Osteogenic cells differentiate into chondroblasts. As a result, cartilage tissue (cartilaginous callus) forms in the injury zone.
- At high $O_2$ levels: With adequate blood supply, the cambium elements transform into osteoblasts, and full-fledged bone tissue is formed.
This is why maintaining blood flow in the trauma area is crucial for proper fracture union.
Bone Tissue Nutrition Features
Unlike cartilage, bone tissue strictly requires blood vessels.
The main reason for this lies in the physicochemical properties of bone. The extracellular matrix here has a high density and pronounced mineralization. At significant bone thicknesses, this makes the nutrition of cells (osteocytes) by simple diffusion of nutrients—as seen in cartilage tissue—impossible.
The periosteum acts as a source of vascularization: branches depart from its vascular network and penetrate deep into the bone matrix via specialized perforating canals, ensuring the trophic supply of internal structures.
Pathway of Substance Transport
The delivery of oxygen and nutrients from periosteal vessels to every bone cell represents a complex, multi-step system. Transport occurs along the following route:
- Vessels (capillaries) $\rightarrow$ Perivascular spaces (zones around vessels) $\rightarrow$ Canaliculi (microscopic channels housing osteocyte processes) $\rightarrow$ directly to Osteocytes.
This chain maintains cell viability even amidst a dense, calcified extracellular matrix.