Page 246 - Atlas of Histology with Functional Correlations

FUNCTIONAL CORRELATIONS 7.2 ■ Cartilage

(Hyaline, Elastic, and Fibrocartilage)

Cartilage is nonvascular, but it is surrounded by vascular connective tissue,
the perichondrium. Because of the high water (hydration) content in the

cartilage, all nutrients enter and metabolites leave the cartilage by diffusing
through the matrix. Also, the cartilage matrix is soft and pliable, not as hard
or rigid as bone. As a result, cartilage can simultaneously grow by two
different processes: interstitial growth and appositional growth.

Interstitial growth involves mitosis of chondroblasts within the matrix

and deposition of new matrix between and around the new cells. This process
increases cartilage growth and size from within. In contrast, appositional
growth occurs on the periphery of the cartilage. Here, chondroblasts

differentiate from the inner chondrogenic cellular layer of the perichondrium
and deposit a layer of cartilage matrix that is apposed to the existing cartilage
layer. This growth process increases cartilage width.

Hyaline cartilage provides a firm structural and flexible support. Elastic
cartilage with branching elastic fibers confers structural support as well as

increased flexibility. In contrast to hyaline cartilage, which can calcify with
aging, the matrix of elastic cartilage does not calcify, and the cartilage
maintains its high flexibility.

Fibrocartilage is a tough, strong component that provides support for the

body, especially in the vertebral column of the intervertebral disks. The main
function of fibrocartilage is to provide tensile strength, bear weight, and
resist stretch or compression. This cartilage type is always dense and filled
with strong, thick type I collagen fibers and chondrocytes.

FIGURE 7.6 | Elastic Cartilage: Epiglottis

Elastic cartilage differs from hyaline cartilage by the presence of numerous

elastic fibers (4) in its matrix (7). Staining the cartilage of the epiglottis with
silver reveals thin elastic fibers (4) that enter the cartilage matrix from the
surrounding connective tissue perichondrium (1) and are distributed as
branching and anastomosing fibers. The density of the fibers varies among
elastic cartilages as well as among different areas of the same cartilage.

245