Cartilage consists of cells and intercellular substance. Intercellular substance (matrix), in its turn, consists of amorphous substance and fibres (mainly collagen).
HYALINE CARTILAGE. The word “hyaline” is derived from the Greek hyalos, meaning glass. Hyaline cartilage appears as a translucent, bluish-white mass in the fresh condition. It forms the articular surfaces of bones within joints, the costal cartilages, and the cartilages of the nose, larynx, trachea, and bronchi. In the fetus nearly all the skeleton is first laid down as hyaline cartilage, which is replaced later by bone.
The cells. The cartilage cells, or chondrocytes, occupy small cavities or lacunae within the matrix (intercellular substance). The cells usually are ovoid or spherical, and each contains a large, spherical, centrally placed nucleus with one or more nucleoli. The surface of each cell is irregular and has short processes that extend into depressions within matrix. The cytoplasm is finely granular and moderately basophil, due to the presence of abundant free ribosomes and of a relatively well-developed granular endoplasmic reticulum; in additions, it contains a prominent Golgi complex, large mitochondria, vacuoles, fat droplets, and some glycogen.
In the centre of a mass of cartilage in the adult, the cells may be arranged in groups, each group representing the offspring of a single parent chondrocyte. Such a group of cells within a single lacuna is referred to as a cell nest or isogenous group. Toward the periphery of a mass of cartilage the cells are elliptical and flattened parallel to the surface. In fetal cartilage the cells often are flattened and cell nests are seen rarely.
The matrix (intercellular substance).
1) Collagenous fibres;
2) Amorphous (ground) substance. The ground substance of cartilage is markedly basophil owing to its content of proteoglycans.
ELASTIC CARTILAGE. Elastic cartilage is similar in many ways to hyaline cartilage. The main difference is that the matrix contains both collagen and elastic fibres. This type of cartilage occurs in locations where support with flexibility is required, as in the external ear, auditory tube, epiglottis, and certain cartilages in larynx.
FIBROCARTILAGE..
1) The cells. These may occur singly or in groups, but commonly are in short rows.
2) Matrix (intercellular substance) consists of collagen fibres and amorphous substance.
Fibrocartilage lacks a perichondrium.
BONE
Bone consists of:
1) bone cells;
2) intercellular substance:
a. amorphous (ground) substance, in which mineral salts (mainly calcium and phosphorus) are deposited;
b. collagen fibres.
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