Bone Tissue and the Skeletal System

Overview of the Skeletal System

The adult human skeletal system is composed of 206 bones, along with associated cartilage and ligaments. Bone tissue, or osseous tissue, is a specialized connective tissue that forms the rigid part of the skeleton. Cartilage and ligaments also play essential roles in skeletal structure and function.

• 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: Stores energy in the form of fat within yellow bone marrow.

• Acid-Base Balance: Buffers blood against pH changes using alkaline salts.

Cartilage: Structure, Types, and Locations

Types of Cartilage

Cartilage is a flexible connective tissue found in various parts of the body. It is classified into three main types based on fiber 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, trachea), nasal cartilage.

• Elastic Cartilage:

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

  • Locations: External ear, epiglottis.

• Fibrocartilage:

  • Contains thick collagen fibers, providing great tensile strength.

  • Locations: Intervertebral discs, menisci of knee, pubic symphysis.

Growth of Cartilage

Cartilage grows by two mechanisms:

• Appositional Growth:

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

  • Results in increased width of cartilage.

• Interstitial Growth:

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

  • Results in increased length and internal expansion of cartilage.

Classification of Bones

Bone Types and Functions

Bones are classified by their shapes, which relate to their functions in the body. The main types are:

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

• Short Bones: Provide stability and support with limited motion (e.g., carpals, tarsals).

• Flat Bones: Protect internal organs and provide surfaces for muscle attachment (e.g., sternum, ribs, cranial bones).

• Irregular Bones: Have complex shapes for specialized functions (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:

Example: The femur is a long bone that acts as a lever to facilitate walking and running, while the patella is a sesamoid bone that protects the knee joint.