Cartilage: Structure, Growth and Repair Quiz

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In growing cartilage, which statement best distinguishes chondroblasts from chondrocytes?

A Chondrocytes maintain matrix in lacunae but cannot divide to support growth from within
B Chondrocytes form the fibrous perichondrium, while chondroblasts produce type I collagen only
C Chondroblasts synthesise matrix at growing surfaces and become chondrocytes once enclosed in lacunae ✓
D Chondroblasts are marrow-derived blood cells that replace chondrocytes after every load cycle
E Chondrocytes synthesise matrix only at free surfaces, while chondroblasts occupy lacunae deep in adult tissue

The answer is C: Chondroblasts synthesise matrix at growing surfaces and become chondrocytes once enclosed in lacunae

Explanation

Why C is correct

See Cells and Matrix. Option C is correct because the two names describe the same cell at different moments. A chondroblast is an active, matrix-secreting cell found where cartilage is growing or being remodelled, for example just under the perichondrium (the fibrous sheath that wraps many cartilages). The matrix is the gel and fibre mixture that makes up most of the tissue. As the chondroblast secretes it, the cell gradually surrounds itself. Once it is trapped inside its own product, sitting in a small cavity called a lacuna (plural lacunae), it is renamed a chondrocyte. Chondrocytes are the mature cells that maintain the matrix by balancing synthesis against limited breakdown, and they work slowly because cartilage is a low-metabolism, low-cell-density tissue. So the change of name reflects position and activity, not a new cell type arriving from elsewhere. A useful memory aid is that the ending -blast marks an immature, matrix-building cell, whereas -cyte marks a mature cell that has settled in and looks after what it built.

Chondroblast: an active, matrix-secreting cell found where cartilage is growing at the surface.
Chondrocyte: the mature cell, enclosed in a lacuna, that maintains the matrix.
One cell, two names: the name changes with position and activity, not with a new cell type.

Why the other options are incorrect

A. Chondrocytes maintain matrix in lacunae but cannot divide to support growth from within: Chondrocytes can still divide inside the matrix, which is how cartilage grows from within (interstitial growth). The daughter cells stay together as small groups until new matrix separates them.
B. Chondrocytes form the fibrous perichondrium, while chondroblasts produce type I collagen only: The perichondrium is the fibrous connective-tissue sheath around many cartilages, and it is not made by chondrocytes. Chondroblasts also make the cartilage matrix (type II collagen in hyaline cartilage), so they are not limited to type I collagen.
D. Chondroblasts are marrow-derived blood cells that replace chondrocytes after every load cycle: Cartilage cells are not blood cells and are not recruited from the marrow each time the joint is loaded. Cartilage has no blood supply, and its cells come from the connective-tissue lineage that makes cartilage itself.
E. Chondrocytes synthesise matrix only at free surfaces, while chondroblasts occupy lacunae deep in adult tissue: This reverses the two roles. Matrix is laid down by chondroblasts at growing surfaces, and the cells deep in the tissue, sitting in lacunae, are the chondrocytes. The statement would only be right if the two names were swapped.

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More questions from this set. Start the quiz to answer them and see each explanation.

1
Why can articular cartilage not use conventional appositional growth at its joint surface?
2
Why does hyaline cartilage need both type II collagen and aggrecan to behave normally under load?

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