Cartilage - Anatomy & Physiology

Structure and Function of Cartilage

The function of cartilage is to resist compression, provide resilience and support at sites where flexibility is desired.

Structure

Chondrocytes

Reside within lacunae within ECM and are responsible for synthesizing the matrix. The matrix consists of type II collagen, (except fibrocartilage) and proteoglycans with associated glycosaminoglycans. They are continually turned over and are the most vulnerable component of cartilage. Decresed proteoglycan, causes loss of lubrication which results in collagen disruption. This includes, frays, clefts, fibrillation, ulcers, exposure of bone, eburnation, +/- osteophytes and joint mice.

Cartilage is avascular, nutrients and waste move via diffusion. The perichondrium surrounding the cartilage is composed of two layers:

1. Fibrous- outer, dense irregular connective tissue.

2. Chondrogenic- inner, flattened cells that differentiate to chondrocytes.

Types of Cartilage

Hyaline Cartilage

The most abundant in the body. It is normally blue-white, smooth with a moist surface and turns yellow and becomes thinner in old age. It is found in nose, trachea, bronchi, ventral ends of ribs and sternal attachment. It is surrounded by perichondrium. It is at sites of articulation to provide a resilient, frictionless surface that resists compression. It is also found at epiphyseal growth plates.

Elastic Cartilage

Elastic cartilage has a yellow appearance and is found in auricular cartilage, larynx, eustacian tube, and epiglottis. It is surrounded by perichondrium and has resiliance with added flexibility.

Fibrocartilage

Fibrocartilage has more collagen (Type I) and less proteglycans than hyaline. It resists high tensional strain and is often in transition with hyaline. It is found in intervertebral discs, tendon/ligament attachment to bone, joint menisci, and articular surface of some joints (such as the temperomandibular). It has NO perichondrium.