Cartilage and Bone: Structural Connective Tissue

Skeletal System

The skeletal system is an organ system composed of dynamic, living tissues and organs that are constantly growing and remodeling. It provides structural support, protection, and serves as a reservoir for minerals.

• Components: Bones, cartilage, ligaments, and other supportive connective tissues.

• Mineral Storage: Bones act as a major storage and source of calcium ions (Ca2+) and phosphate ions (PO43-).

Cartilage

Cartilage is a semi-rigid connective tissue found throughout the body. It is not as strong as bone but is more flexible and resilient, playing a crucial role in the skeletal system.

• Chondroblasts: Cells that begin to produce the extracellular matrix of cartilage.

• Chondrocytes: Mature cartilage cells that continue to produce matrix and become surrounded by it.

• Lacunae: Small spaces within the matrix that house chondrocytes.

• Avascular: Mature cartilage lacks blood vessels, relying on diffusion for nutrient and waste exchange.

Functions of Cartilage

Cartilage serves several essential functions in the body:

• Support of Soft Tissue: Provides structural support to soft tissues such as the respiratory tree and the auricle (external ear).

• Articulations: Forms smooth, gliding surfaces at joints where bones meet, reducing friction and enabling movement.

• Precursor Model for Bone Growth: Serves as a template for the formation of bones during development (endochondral ossification).

Types of Cartilage

There are three major types of cartilage, each with distinct properties and locations:

• Hyaline Cartilage: The most abundant type, found in the respiratory system, joints, and fetal skeleton. It has a translucent matrix with no visible protein fibers, making it flexible and resilient. Surrounded by a dense connective tissue called the perichondrium.

• Fibrocartilage: Found in areas requiring strength, such as the knee joint, intervertebral discs, and pubic symphysis. Contains thick collagen fibers in the matrix, acts as a shock absorber, and is not surrounded by perichondrium.

• Elastic Cartilage: Located in regions needing flexible support, such as the auricle (ear) and epiglottis. Contains highly branched elastic fibers in the matrix for flexibility and is surrounded by perichondrium.

Distribution of Cartilage

Cartilage is distributed throughout the body in specific locations, each type serving specialized functions:

Example: The meniscus in the knee is composed of fibrocartilage, providing cushioning and resistance to compression during movement.

Additional info: Cartilage injuries heal slowly due to the avascular nature of mature cartilage, which limits nutrient supply and cellular repair mechanisms.