Page 63 - Headlines Histology2024_Neat

• Chondroblasts in the midsection of the cartilage model mature, enlarge
and become separated by a very thin layer of intercellular matrix. Such
region is then called a primary center of ossification.

• The enlarged chondroblasts release matrix vesicles that initiate
mineralization.

• The deposition of calcium salts prevents the chondroblasts from receiving
adequate nutrition and results in their death.

• The perichondrium of the shaft assumes osteogenic potential and starts
to lay down a thin layer of bone around the midsection of the cartilage
model referred as periosteal band or bony collar.

• After degeneration of the chondrocytes, some primitive mesenchymal
cells and blood vessels invade the spaces left within the shaft and
differentiate into osteoblasts.

• The osteoblasts cluster around fragments of calcified cartilage and begin
to secrete osteoid that is followed by mineralization.

• Such activity continues until bony trabecullae form that has cores of
calcified cartilage. Such trabecullae are called primary spongiosa.

• The capillaries from the primary center of ossification continue to invade
the model toward both epiphyses that extends bone formation
throughout the cartilage model.

• The periosteum continues to add bone to the periphery, and the primary
spongiosa in the center is resorbed by osteoclasts, thus forming the
marrow cavity, which become filled with the hemopoietic tissue.

• Secondary center of ossification occurs in the epiphysis of larger long
bone. Ossification replaces all the epiphyseal cartilage except a
transverse disk of cartilage is left between the diaphysis and epiphysis.

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