Page 241 - Atlas of Histology with Functional Correlations

PERICHONDRIUM

Most of the hyaline and elastic cartilage is surrounded by a peripheral layer of
vascularized, dense, irregular connective tissue called the perichondrium. Its

outer fibrous layer contains type I collagen fibers, fibroblasts, blood vessels, and
nerves. The inner layer of perichondrium is cellular and contains undifferentiated
mesenchymal cells, which differentiate into chondroblasts that secrete the
external cartilage matrix. On the articulating surfaces of bones, however, hyaline

cartilage is not lined or covered by perichondrium. Similarly, because
fibrocartilage is always associated with dense connective tissue collagen fibers,
it lacks the perichondrium seen in other cartilage.

CARTILAGE MATRIX

Cartilage matrix is produced and maintained by chondrocytes and

chondroblasts. The collagen or elastic fibers give cartilage matrix its firmness
and resilience. Similar to loose connective tissue, the extracellular ground
substance of cartilage contains sulfated glycosaminoglycans and hyaluronic
acid that bind with elastic and collagen fibers in the ground substance.
Embedded within the cartilage matrix are collagen and elastic fibers, whose

concentration determines whether the cartilage is hyaline, elastic, or
fibrocartilage.

Hyaline cartilage matrix consists of the fine type II collagen fibrils
embedded in a firm, amorphous hydrated matrix that is rich in proteoglycans and

structural glycoproteins. Most proteoglycans in the cartilage matrix exist as large
proteoglycan aggregates with sulfated glycosaminoglycans linked to core
proteins and nonsulfated glycosaminoglycan hyaluronic acid. The proteoglycan
aggregates bind to the thin fibrils of the collagen matrix. The negatively charged

glycosaminoglycan sulfated ions attract water molecules and hydrate the
cartilage matrix. Hydrated cartilage matrix allows diffusion of molecules to and
from the chondrocytes and allows cartilage to resist compression. Because of its
hydration, cartilage can also act as a shock absorber in different parts of the

body.

In addition to type II collagen fibrils and proteoglycans, cartilage matrix also
contains an adhesive glycoprotein called chondronectin. These macromolecules

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