Bone Tissue and the Skeletal System

Overview of the Skeletal System

The adult human skeletal system consists of 206 bones and is composed of several types of connective tissues, including osseous (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, hardened by minerals such as calcium phosphate.

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

• Perichondrium: A dense connective tissue layer surrounding cartilage, providing support and resisting outward expansion.

• Ligaments: Connect bones together at joints, contributing to stability.

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: Yellow bone marrow stores fat as an energy reserve.

• 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 composition and function:

• Hyaline cartilage:

  • Most abundant type; provides support, flexibility, and resilience.

  • 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 greater flexibility.

  • Locations: External ear, epiglottis.

• Fibrocartilage:

  • Contains thick collagen fibers, providing 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 on the surface of existing cartilage.

  • Results in increased thickness.

• Interstitial growth:

  • Chondrocytes within lacunae divide and secrete new matrix from within.

  • Results in increased length.

Classification of Bones

Bone Types and Their Functions

Bones are classified according to 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 with limited 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; protect tendons from compressive forces (e.g., patella).

Bone Classification Table

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

Key Terms and Concepts

• Osseous tissue: Bone tissue, characterized by a hardened matrix due to mineral deposition.

• Perichondrium: Dense connective tissue layer surrounding cartilage.

• Chondrocytes: Cartilage cells located in lacunae.

• Lacunae: Small spaces within cartilage or bone that house cells.

Example Application

Long bones such as the femur act as levers to facilitate movement, while flat bones like the sternum protect vital organs such as the heart and lungs.

Additional info: The classification and structure of bones are fundamental for understanding bone growth, development, and the impact of diseases such as osteoporosis and fractures.