Study Notes: Introduction to the Skeletal System

Introduction to the Skeletal System

Overview of the Skeletal System

The skeletal system is a complex organ system composed of tissues that grow and change throughout life. It provides the structural framework for the body and is essential for movement, protection, and support.

• Bones: Rigid organs that form the skeleton and provide support and protection.

• Cartilages: Flexible connective tissues that cushion joints and aid in movement.

• Ligaments: Bands of connective tissue that connect bones to other bones.

• Other supportive connective tissues: Includes tendons and other structures that contribute to skeletal function.

Functions of the Skeletal System

• Support: Provides a framework for the body and supports soft tissues.

• Protection: Shields vital organs such as the brain, heart, and lungs.

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

• Mineral Storage: Stores minerals such as calcium and phosphorus.

• Blood Cell Production: Houses bone marrow, which produces blood cells.

Skeletal System: Cartilage

Structure and Types of Cartilage

Cartilage is a semi-rigid connective tissue that provides flexibility and support in various parts of the body. It is less rigid than bone but more rigid than other connective tissues.

• Chondroblasts: Cells that produce the cartilage matrix.

• Chondrocytes: Mature cartilage cells that are surrounded by matrix and reside in small spaces called lacunae.

Functions of Cartilage

• Support soft tissues: Forms structures such as the external ear and nose.

• Articulations: Cushions joints and reduces friction between bones.

• Precursor model for bone growth: Serves as a template for the development of bones during embryogenesis.

Types of Cartilage

• Hyaline cartilage: Most common type; found in the nose, trachea, and at the ends of long bones.

• Fibrocartilage: Contains thick collagen fibers; found in intervertebral discs and pubic symphysis.

• Elastic cartilage: Contains elastic fibers; found in the external ear and epiglottis.

Skeletal System: Growth of Cartilage

Patterns of Cartilage Growth

Cartilage grows by two main mechanisms: interstitial growth and appositional growth.

Interstitial Growth (Growth from Inside)

• Mitotic division of chondrocytes in lacunae: Each lacuna may contain two chondrocytes.

• Matrix synthesis: Chondrocytes synthesize and secrete new matrix.

• Separation: The new matrix separates the cells, allowing cartilage to expand from within.

Appositional Growth (Growth from Outside)

• Division of stem cells in perichondrium: Stem cells at the periphery divide to produce chondroblasts.

• Matrix production: Chondroblasts produce matrix and become chondrocytes, forming new lacunae.

• Addition to existing matrix: New layers of cartilage are added to the surface.

Comparison of Cartilage Growth Types

Growth Type	Location	Process
Interstitial	Within cartilage	Chondrocytes divide and secrete matrix internally
Appositional	Periphery of cartilage	Stem cells in perichondrium produce new chondroblasts and matrix externally

Example: Cartilage Growth in Long Bones

During childhood and adolescence, cartilage growth at the epiphyseal plates allows long bones to lengthen, contributing to overall growth.

Additional info: Cartilage is avascular, meaning it does not contain blood vessels; nutrients diffuse through the matrix to reach chondrocytes.