Bone Tissue and the Skeletal System

Overview of the Skeletal System

The skeletal system in adult humans consists of 206 bones and is composed primarily of osseous tissue (bone tissue), cartilage, and ligaments. These components work together to provide structure, protection, and movement for the body.

• Osseous tissue: The main tissue forming bones.

• Cartilage: Forms most embryonic bones and covers many joint surfaces in the mature skeleton.

• Perichondrium: A layer of dense connective tissue surrounding cartilage, acting as a girdle to resist outward expansion.

• Ligaments: Connect bones together at joints.

Functions of the Skeletal System

• Support: Provides a framework for the body.

• Protection: Shields vital organs (e.g., skull protects the brain).

• Movement: Acts as levers for muscles to produce movement.

• Electrolyte balance: Stores minerals such as calcium (Ca) and phosphorus (P).

• Triglyceride (fat) storage: Stores energy in the form of fat within yellow bone marrow.

• Acid-base balance: Alkaline salts in bone buffer blood against pH changes.

Cartilage: Structure, Types, and Locations

Types of Cartilage

Cartilage is a flexible connective tissue found in various locations throughout the body. It is classified into three main types based on structure and function:

• Hyaline cartilage:

  • Provides support, flexibility, and resilience.

  • Most abundant type; contains only collagen fibers.

  • Locations: Articular surfaces of joints, costal cartilage (ribs), respiratory structures (larynx), nasal cartilage (nose tip).

• Elastic cartilage:

  • Similar to hyaline cartilage but contains elastic fibers for added flexibility.

  • Locations: External ear, epiglottis.

• Fibrocartilage:

  • Contains thick collagen fibers, providing great tensile strength.

  • Locations: Menisci of knee, intervertebral discs, pubic symphysis.

Growth of Cartilage

Cartilage grows by two mechanisms:

• Appositional growth:

  • Cartilage-forming cells in the perichondrium secrete new matrix against the external face of existing cartilage.

  • Results in new matrix being laid down on the surface.

• Interstitial growth:

  • Chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within.

  • New matrix is made within the cartilage itself.

Classification of Bones

Bone Types and Their Functions

Bones are classified based on their shapes and functions. Each type plays a specific role in the skeletal system:

• Long bones: Act as levers for movement (e.g., humerus, femur).

• Short bones: Provide stability and support, allowing some motion (e.g., carpals, tarsals).

• Flat bones: Serve as points of muscle attachment and protect internal organs (e.g., sternum, ribs, scapulae, cranial bones).

• Irregular bones: Have complex shapes and protect internal organs (e.g., vertebrae, facial bones).

• Sesamoid bones: Small, round bones embedded in tendons, protecting tendons from compressive forces (e.g., patella).

Bone Classification Table

The following table summarizes the main bone classifications, their features, functions, and examples:

Example:

The femur is a long bone that acts as a lever for movement, while the patella is a sesamoid bone embedded in the tendon of the quadriceps muscle, protecting the tendon from compressive forces during knee extension.

Additional info: Bone classification is essential for understanding skeletal anatomy, clinical assessment, and the functional adaptation of bones to mechanical stress.