Which zone features cartilage cells that have grown large and are about to be replaced by bone?

Which zone features cartilage cells that have grown large and are about to be replaced by bone?

• A. Resting (reserve) zone
• B. Proliferation zone
• C. Calcification zone
• D. Hypertrophy zone

Answer: (D)

Chondrocyte hypertrophy signals preparation for bone formation. In the growth plate, cartilage cells progress from resting to proliferating to hypertrophy, where they grow large and stack in columns. This enlargement pushes the surrounding cartilage toward the next zone and prepares the matrix for calcification. Soon after, these enlarged cells die, the matrix becomes calcified, and osteoblasts invade to lay down bone. That combination of “getting large and nearing replacement by bone” is the hallmark of the hypertrophy zone. Other zones don’t fit as well: the resting zone has small, inactive cells; the proliferative zone contains rapidly dividing cells but not enlarged ones; the calcification zone involves matrix calcification and cell death rather than cells that have grown large in preparation for replacement.

Chondrocyte hypertrophy signals preparation for bone formation. In the growth plate, cartilage cells progress from resting to proliferating to hypertrophy, where they grow large and stack in columns. This enlargement pushes the surrounding cartilage toward the next zone and prepares the matrix for calcification. Soon after, these enlarged cells die, the matrix becomes calcified, and osteoblasts invade to lay down bone. That combination of “getting large and nearing replacement by bone” is the hallmark of the hypertrophy zone.

Other zones don’t fit as well: the resting zone has small, inactive cells; the proliferative zone contains rapidly dividing cells but not enlarged ones; the calcification zone involves matrix calcification and cell death rather than cells that have grown large in preparation for replacement.