In the zone of ossification of the epiphyseal plate.
a. chondrocytes are actively dividing.
b. chondrocytes are maintained in a reserve to divide if needed.
c. chondrocytes begin to enlarge in their lacunae as they mature.
d. chondrocytes are calcified and abut the diaphysis with osteoblasts.
The Correct Answer and Explanation is :
The correct answer is:
d. chondrocytes are calcified and abut the diaphysis with osteoblasts.
Explanation:
The epiphyseal plate (growth plate) is a specialized cartilage structure responsible for longitudinal bone growth during development. It is divided into zones, each with specific cellular activities:
- Resting Zone:
- This zone contains small, inactive chondrocytes that serve as a reserve. These cells are not actively dividing but are essential for sustaining growth.
- Proliferation Zone:
- In this zone, chondrocytes are actively dividing and aligning in columns. This activity is critical for elongating the bone.
- Hypertrophic Zone:
- Here, chondrocytes cease dividing and enlarge within their lacunae. This zone is characterized by the swelling of cells and the beginning of matrix remodeling.
- Zone of Calcification/Ossification:
- In this zone, the chondrocytes undergo apoptosis (cell death) and the surrounding cartilage matrix calcifies. The calcified cartilage serves as a scaffold for bone formation.
- Osteoblasts from the adjacent diaphysis invade the calcified cartilage matrix. These osteoblasts deposit bone matrix, replacing the calcified cartilage with new bone tissue. This process is integral to bone elongation.
The zone of ossification abuts the diaphysis, which is the shaft of the long bone. The transformation of calcified cartilage into bone ensures that the bone grows in length while maintaining structural integrity.
Thus, in the zone of ossification, the primary activity involves the calcification of chondrocytes, their replacement with osteoblasts, and the deposition of new bone tissue. This process marks the transition from cartilage-based growth to bone elongation and strength development, crucial for the function and durability of the skeletal system.