Slide DMS068 [Developing bone]. Orient the section using your lowest power objective and the above diagram. Identify: epiphysis, metaphysis, marrow cavity, diaphyseal bone, and periosteum. Note that with the staining technique used here, the hyaline cartilage of the epiphyseal hyaline cartilage matrix stains faintly acidophilic; calcified cartilage, dark purple; bone, bright red.
Using low and high power, study the epiphysis-diaphysis junction region in more detail. Working from the epiphysis toward the diaphysis, identify:
1. Zone of reserve ("resting") cartilage (unmodified hyaline).
2. Zone of proliferating cartilage . . . clusters (cell nests) of chondrocytes undergo successive mitotic divisions to form columns of cells separated by deeply staining matrix.
3. Zone of maturing cartilage . . . cell division ceases, chondrocytes increase in size.
4. Zone of hypertrophy and calcification . . .hypertrophied chondrocytes dying or lysed away, matrix material calcified, invasion of capillaries osteogenic cells.
5. Metaphyseal (osteogenic) zone . . .lamellae of new bone deposited on remnants of calcified cartilage.
Observe the osteoblasts covering the lamellae of new bone (some may have been detached during preparation of the section). Additional osteoblasts are seen lining the walls of the marrow cavity of the diaphysis - - - these constitute the endosteum of the bone. Note the numerous blood vessels in the marrow adjacent to the bone trabeculae. What is the origin of osteoblasts?
Find osteoclasts attached to the bone trabeculae in, just below, and lateral to the metaphyseal region. (Do not confuse these giant, multinucleated cells with another type of giant cell, megakaryocytes, found in the bone marrow. The latter are not multinucleated.) What is the function of osteoclasts? What is their origin?
Look for early signs of secondary ossification center development in the epiphysis (may not be present in all slides).
From the foregoing observations and your textbook reading, be prepared to explain how long bones grow in length and width and how during growth they undergo modeling to maintain their typical shapes.