Cartilage

Cartilage is usually found in close association with bone in the body. It is a type of connective tissue which is tough, semi-transparent, elastic and flexible. The matrix or ground substance of cartilage consists mainly of glyco-protein material, chondroitin. The cartilage cells (chondrocytes) lie scattered in the matrix. Cartilage is covered by a dense fibrous membrane, the perichondrium. No nerves or blood vessels occur in cartilage.

In some vertebrates, such as sharks, the entire skeleton is made up of cartilage. In mammal embryos, the skeleton first forms as cartilage tissue. Cartilage acts as a model and is gradually replaced by bone as the embryo grows. Such cartilage is known as temporary cartilage. The process by which bone tissue follows the cartilage model and slowly replaces it is known as ossification. Permanent cartilage (cartilage which does not become ossified) is found in the tip of the nose, in the external ear and in the walls of the trachea (windpipe) and the larynx (voice-box).

Hyaline cartilage is semi-transparent and appears bluish-white in colour. It is extremely strong, but very flexible and elastic. Hyaline cartilage consists of living cells, chondrocytes, which are situated far apart in fluid-filled spaces, the lacunae. There is an extensive amount of rubbery matrix between the cells and the matrix contains a number of collagenous fibres. Hyaline cartilage occurs in trachea, the larynx, the tip of the nose, in the connection between the ribs and the breastbone and also the ends of bone where they form joints. Temporary cartilage in mammalian embryos also consists of hyaline cartilage.

Functions

• Reduces friction at joints.

  By virtue of the smooth surface of hyaline cartilage, it provides a sliding area which reduces friction, thus facilitating bone movement.

• Movement

  Hyaline cartilage joins bones firmly together in such a way that a certain amount of movement is still possible between them.

• Support

  The c-shaped cartilagenous rings in the windpipes (trachea and bronchi) assist in keeping those tubes open.

• Growth

  Hyaline cartilage is responsible for the longitudinal growth of bone in the neck regions of the long bones.

White fibrocartilage is an extremely tough tissue. The orientation of the bundles depends upon the stresses acting on the cartilage. The collagenous bundles take up a direction parallel to the cartilage. Fibrocartilage is found as discs between the vertebrae between the pubic bones in front of the pelvic girdle and around the edges of the articular cavities such as the glenoid cavity in the shoulder joint.

Functions

• Shock absorbers.

  The cartilage between the adjacent vertebrae absorbs the shocks that will otherwise damage and jar the bones while we run or walk.

• Provides sturdiness without impeding movement.

  The white fibrocartilage forms a firm joint between bones but still allows for a reasonable degree of movement.

• Deepens sockets.

  In articular cavities (such as the ball-and-socket joints in the hip and shoulder regions) white fibrocartilage deepens the sockets to make dislocation less possible.

Basically elastic cartilage is similar to hyaline cartilage, but in addition to the collagenous fibres, the matrix of the elastic also contains an abundant network of branched yellow elastic fibres. They run through the matrix in all directions. This type of cartilage is found in the lobe of the ear, the epiglottis and in parts of the larynx.

Functions

• Maintain shape.

  In the ear, for example, elastic cartilage helps to maintain the shape and flexibility of the organ.

• Support

  Elastic cartilage also strengthens and supports these structures.

Types of Cartilage.

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