The Skeletal System

Overview and Functions

The human skeletal system is composed of 206 bones in adults and serves as the framework for the body. It is made up of osseous tissue (bone), cartilage, and ligaments. Each component plays a vital role in the structure and function of the skeleton.

• Support: Provides structural support for the entire body.

• Protection: Shields vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

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

• Electrolyte Balance: Stores minerals such as calcium (Ca) and phosphate (P), essential for various physiological processes.

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

• Acid-Base Balance: Buffers blood against excessive 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 skeleton. It is surrounded by the perichondrium, a dense connective tissue layer that resists outward expansion.

• Hyaline Cartilage: Most abundant type; provides support, flexibility, and resilience. Contains only collagen fibers. Found in articular surfaces of joints, costal cartilage (ribs), respiratory structures (larynx), and nasal cartilage (nose tip).

• Elastic Cartilage: Similar to hyaline cartilage but contains elastic fibers, allowing for greater flexibility. Located in the external ear and epiglottis.

• Fibrocartilage: Contains thick collagen fibers, providing great tensile strength. Found in the menisci of the knee and intervertebral discs.

Growth of Cartilage

• Appositional Growth: Cartilage-forming cells in the perichondrium secrete new matrix on the external surface of existing cartilage, increasing its size.

• Interstitial Growth: Chondrocytes within lacunae divide and secrete new matrix from within, expanding cartilage internally.

Classification of Bones

Bone Types and Functions

Bones are classified based on their shapes and functions. Each type is adapted for specific roles in the body.

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

• 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 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.