This PS illustrates the PHYSIS or epiphyseal plate (left of the tip of arrowhead) and metaphysis and diaphysis (right of tip of the arrowhead). The INTERSTITIAL GROWTH of the hyaline cartilage of the physis accounts for the bone growing in length. The physis (epiphyseal plate) becomes the EPIPHYSEAL LINE in the adult. THE FOLLOWING ZONES THAT MAKE UP THE PHYSIS (EPIPHYSEAL PLATE) ARE AS FOLLOWS:
A. ZONE OF RESERVE CARTILAGE (r)
1. This is the layer where you find inactive chondrocytes in an irregular arrangement.
2. This area is adjacent to the zone of proliferation.
B. ZONE OF PROLIFERATION (p)
1. This area is depicted by the presence of mitotically active chondrocytes.
2. In this zone the chondrocytes align themselves in rows or columns (resemble a stack of poker chips).
3. Major contribution to lengthening of the bone.
C. ZONE OF MATURATION (HYPERTROPHY) (m)
1. No mitosis here
2. Chondrocytes and lacunae enlarge (hypertrophy)
3. Contribute to lengthening of the bone
D. ZONE OF CALCIFICATION (c)
1. Chondrocytes and lacunae are at maximum size
2. Intercellular matrix of the longitudinal septa ONLY is calcified
3. Chondrocytes may die in this zone, due to the deposition of calcium which inhibits nutrient dispersion
4. Has "honey comb" appearance
The following zones are part of the METAPHYSIS (the flared portion of the diaphysis):
A. ZONE OF RESORPTION (r)
1. "Honey comb" appearance of adjacent zone of the epiphyseal plate is broken down by osteoclasts within this zone
2. All the dead cells of the calcification zone are removed, leaving some of the intercellular cartilage matrix
3. This is the approximate area of the metaphysis
4. This area has no osteoid
B. ZONE OF OSSIFICATION (a)
1. Identify by noting the deposition of osteoid (acidophilic material) upon the hyaline cartilage matrix remnant (note this is not cartilage because no chondrocytes are present.
2. Bone only grows by appositional growth whereas cartilage grows by appositional and interstitial growth.
