Chondrocytes in Cartilage

Cartilage Cells (Chondrocytes)

• Chondrocytes are variable in size and shape, with larger cells being more differentiated and smaller cells being less differentiated.
• They have rounded nuclei and vacuolated cytoplasm.
• Chondrocytes are present inside a space called lacuna, which can contain one or more cells (called a nest).
• Young chondrocytes synthesize and secrete proteins, tropocollagen, and GAGs of intercellular substance.
• With Electron Microscopy (E/M), chondrocytes demonstrate well-developed RER and Golgi body.
• The cell outline is irregular due to the presence of cytoplasmic processes that extend into the intercellular substance like microvilli.
• In old chondrocytes, the amount of RER and Golgi are less, and glycogen and lipid material accumulate in the cytoplasm.

Matrix of Hyaline Cartilage

• The matrix is composed of a fibrous and an amorphous substance.
• The fibrous part is collagenic fibers (type II) and fibrils.
• The amorphous part is a GAG known as chondroitin sulphuric acid.
• The matrix is condensed around the lacunae, forming the capsule of the territorial matrix, which is strongly basophilic.
• Between lacunae, the matrix is less basophilic and called interterritorial matrix.

Growth of Cartilage

• Interstitial growth occurs within the substance of the cartilage, where immature chondrocytes divide and lay down matrix around them.
• Appositional growth occurs by the inner chondrogenic layer of the perichondrium, where cells divide and differentiate into chondroblasts and chondrocytes.

Cartilage Nutrition and Repair

• Cartilage cells are nourished by means of diffusion.
• Cartilage repair occurs in young cartilage only, while in adults, cartilage damage results in connective tissue scar.

General Characters of Cartilage

• Cartilage is a special type of connective tissue with a plastic appearance and can bear a certain amount of weight.
• It can bend easily but does not stretch.
• The free surface of cartilage is smooth and lubricated, allowing the gliding of two or more cartilage surfaces on each other.
• Cartilage consists chiefly of intercellular substance (matrix) and cells.
• Cartilage is avascular and is nourished by diffusion from blood vessels in the perichondrium.

Functions of Cartilage

• Cartilage is important for free movable joints.
• Cartilage serves as a model for the development of long bones and their increase in length.

Types of Cartilage

• There are three types of cartilage according to the types of fibers in the matrix: Hyaline, Elastic, and Fibrocartilage.

Hyaline Cartilage

• Hyaline cartilage develops from the mesenchyme.
• It has a white glassy translucent appearance.
• Sites: In prenatal life, most of the skeleton is formed of hyaline cartilage. In adult life, it is present in articular surfaces of joints, epiphyseal plate of long bones, nose, larynx, trachea, and bronchi.

The Perichondrium

• The perichondrium is a layer of fibrous CT containing blood vessels that nourish cartilage tissue by diffusion.
• The inner part of the perichondrium contains large numbers of chondrogenic cells and chondroblasts that are active in secretion and form newly formed appositional cartilage.