Growth in Length of Long Bones

What is the resting zone in long bones

The side of the cartilage that is relatively inactive during bone growth; it is on the side of the epiphyseal plate facing the epiphysis

How do cells align below the resting zone

In tall columns, like stacked coins; it allows for fast, efficient growth

What are the zones in growth in length of bones

Proliferation zone, hypertrophic zone, calcification zone, and the ossification zone

What is the proliferation zone

The zone right next to the resting zone; The cartilage cells divide quickly, pushing the epiphysis away from the diaphysis and lengthening the entire bone

What is the hypertrophic zone

The older chondrocytes (closer to the diaphysis) enlarge (hyper trophy). Their lacunae erode and leave large interconnected spaces

What is the calcification zone

The surrounding cartilage matrix calcifies, the chondrocytes die, and the matrix begins to deteriorate. This allows for blood vessels to enter. There are long, slender spicules of calcified cartilage left behind at the epiphysis-diaphysis junction

What is the ossification zone

The calcified spicules are invaded by marrow elements from the medullary cavity. Osteoclasts partially erode the cartilage spicules, then osteoblasts cover them with new bone. Spongy bone then replaces them. The medullary cavity can lengthen as the osteoclasts digest the spicules

Does the epiphyseal plate change its thickness during bone growth

No, it maintains a constant thickness because the rate of cartilage growth on its epiphysis-facing side is balanced by its replacement with bony tissue on its diaphysis-facing side

Does the epiphysis stop remodeling during longitudinal bone growth

No, it is constantly remodeled to maintain proper proportions

When does longitudinal bone growth end

When the epiphysis and diaphysis fuse

When does epiphyseal plate closure occur in males and females

Males - around 21; females - around 18

What cartilage remains when the growth plate closes

Only articulate cartilage