Physiology of Bone Growth
Activity in epiphyseal plate enables bone to grow in length.
Modeling allows bones to grow in diameter.
Remodeling occurs as bone is reabsorbed and replaced by new bone.
Epiphyseal plate is hyaline cartilage plate in metaphysis at each end of long bone.
Epiphyseal Plate
Organized into four zone;
1. Zone of resting cartilage (reserve) zone
2. Zone of proliferating cartilage
3. Zone of maturing cartilage
4. Zone of calcified cartilage
1. Reserve cartilage
Reserve zone is region closest to epiphyseal end of plate and contain small chondrocytes within matrix.
The cell don't function in bone growth (so term rest).
They anchor epiphyseal plate to bone of epiphysis.
2. Proliferative zone
Proliferative zone is next layer toward diaphysis and contain slightly larger chondrocytes arranged like stacks of coin.
It makes new chondrocytes (via mitosis) to replace those that die at diaphyseal end of plate.
3. Zone of maturing cartilage
This zone consist of even larger chondrocytes that arranged in column.
Here chondrocytes produced in zone of proliferation mature and enlarge.
Longitudinal growth of bone is result of cellular division in proliferative zone and maturation of cells in zone of maturation and hypertrophic.
The more mature cells situated closer to diaphyseal end of plate.
4. Zone of calcified cartilage
Most of chondrocytes in zone of calcified matrix, closer to diaphysis, are dead because matrix around them has calcified.
Capillaries and oesteoblasts from diaphysis penetrate this zone, and osteoblast secrete bone tissue on remaining calcified cartilage.
Thus, zone of calcified matrix connect epiphyseal plate to diaphysis.
A bone grows in length when osseous tissues added in diaphysis.
Reserve zone - changes in chondrocytes
Proliferative zone (growing and increasing) - matrix production; mitosis
Maturation and hypertrophy; lipids, glycogen and alkaline, phosphate accumulate matrix calcified.
Calcified matrix
Metaphysis (zone of ossification)
Region between diaphysis and epiphysis of bone where calcified matrix is replaced by bone is called metaphysis.
Growth in Thickness/ Appositional Growth
Appositional growth is responsible for increase in diameter of long bones and increases in size of other bone.
In this process bone lining of medullary cavity is destroyed by osteoclasts, cavity increases in diameter.
At same time, osteoblasts from periosteum add new bone tissue to outer surface.
In cancellous bone, Appositional bone growth adds matrix to outer surface of Trabeculae.
In Compact Bone, Appositional bone growth is responsible for formation of circumferential and concentric lamellae.
0 Comments