NI

Recording-2025-02-14T16_02_15.673Z

Chondrocytes and Chondroblasts

  • Chondrocytes are mature cartilage cells, while chondroblasts are immature cells that create cartilage.

  • The presence and quantity of these cells can vary in different zones of cartilage development.

Zones of Cartilage Growth

Zone of Proliferation

  • In this zone, there is a significant increase in cell number but relatively smaller cell size initially.

  • The cells exhibit a characteristic alignment as they multiply, eventually resulting in larger cells as they divide repeatedly.

  • As cell numbers increase, the surrounding walls of cartilage are pushed apart due to the increased cellular density.

Zone of Calcification

  • At this stage, the cartilage begins to transition into bone by undergoing calcification.

  • Calcium is deposited, which leads to the development of harder cartilage.

  • This marks the end of the cartilage's role, with a noticeable zone of reserve visible.

Mechanisms of Bone Growth

Appositional Growth

  • Bone growth occurs primarily through appositional growth, which increases the thickness of bones.

  • This process is driven by the outer membrane of bones, enabling the skeleton to renew approximately every decade.

Remodeling in Response to Stress

  • Bone remodeling occurs at different rates depending on the mechanical stress applied; e.g., the distal end of the femur is remodeled every six months due to high activity levels.

  • Increased stress can lead to a greater amount of compact bone being formed to adapt to load demands.

Bone Repair Processes

Hematoma Formation

  • Following a fracture, a hematoma, or blood clot, forms at the site of injury.

  • This initial step stabilizes the fracture and begins the healing process.

Callus Formation

  • A soft callus is formed next, consisting of fibrous cartilage and tissue that stabilizes the fracture site.

  • Over time, this develops into a hard callus, which is not as strong as original bone but serves to hold the fracture together.

Long-Term Bone Remodeling

  • After the formation of the hard callus, a prolonged period of remodeling occurs where the bone gradually regains its strength.

  • This is why casts are used post-fracture—to keep the bone stable during the healing process.

Factors Affecting Bone Health

  • Proper intake of calcium, vitamin D, and vitamin K is crucial for maintaining bone strength and preventing conditions like osteomalacia and rickets.

  • Growth hormones, particularly in childhood, play a significant role in regulating chondrocyte proliferation, which impacts growth and development of bones.

Influence of Hormones on Bone Growth

  • Sex hormones (androgens such as estrogen and testosterone) regulate growth and remodeling in bones.

  • Levels of these hormones decrease with age, affecting bone density and health.