Cartilage

Cartilage is a type of elastic connective tissue which acts as rubber-like padding to cover and protect the ends of bones at joints. It is a dense matrix of elastic and collagen fibers which are embedded in rubber like ground substance. The matrix is made by the cells called chondroblasts which then mature are called chondrocytes. They either occur singly or in groups in lacunae (small spaces) in the matrix. Most of the cartilage tissue is surrounded by a membrane of dense and irregular connective tissue named perichondrium.

It is a structural component of the nose, ear, rib cage, intervertebral discs, and bronchial tubes. It is less hard than bones but stiffer and less flexible than muscle tissues. Cartilage serves the purpose of keeping tubes open, due to its rigidity, examples include c-shaped rings of the trachea, the pinna of the ear and the ala of the nostrils.

Cartilage is made up of specialized cells called chondrocytes. The chondrocytes produce a large amount of collagenous extracellular matrix which is rich in elastin fibers and proteoglycans. Cartilage does not possess any blood vessels and nerves, so the nutrition is supplied to tissue through diffusion. On the basis of the amount of collagen, and the type of protein fiber embedded in the matrix of cartilage, it is classified into three types.

Hyaline Cartilage

It is the most abundant of the three types. It is mainly found in bronchi, bronchial tubes, nose, larynx, trachea and costal cartilages. It is also found as a covering in those areas where any injury or wear may cause osteoarthritis, for example, at the ends of long bones and anterior ends of the ribs. Protein fibers in hyaline cartilage are large and mostly collagen. Hyaline cartilage tissues provide smooth surfaces so that tissues can easily slide on each other. They also provide flexibility and support.

Elastic Cartilage

Elastic cartilage is yellowish in color and the chondrocytes are located in a network of elastin fibers within the matrix. It lacks perichondrium. This tissue provides support to the surrounding structures and helps maintain the shape of the area, for example, the pinna of the ear. Examples of elastic cartilage include eustachian tubes, auricle/pinna of the ear and epiglottis.

Fibrocartilage

It is a very tough form of cartilage where chondrocytes are scattered among dense bundles of collagen fibers in the matrix. It also lacks perichondrium. Fibrocartilage is the strongest of the three types of cartilage as it provides rigidity and support to the attached structures. Examples of fibrocartilage include callus (a tissue formed at the site a healing fracture), intervertebral discs, pubic symphysis (the point at which hip bones join at the front of the body), and menisci (the pads of cartilage at knee joints).

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