Bones and Skeletal Tissues

Introduction

The skeletal system is composed of bones and various types of cartilage, providing support, protection, and facilitating movement. Understanding the structure and function of skeletal tissues is fundamental in anatomy and physiology.

Skeletal Cartilage Basics

Structure and Properties

• Skeletal cartilage is primarily composed of water, making it resilient and able to withstand compression.

• Cartilage consists of chondrocytes (cartilage cells) located in small cavities called lacunae within a jelly-like extracellular matrix.

• It is surrounded by the perichondrium, a dense irregular connective tissue that provides nutrients via diffusion, as cartilage is avascular (lacks blood vessels).

Types of Skeletal Cartilage

Hyaline Cartilage

• Most abundant type of cartilage.

• Provides support, flexibility, and resilience.

• Contains only fine collagen fibers.

• Locations: articular (joints), costal (ribs), respiratory (larynx, trachea, bronchi), and nasal cartilage (external nose).

Elastic Cartilage

• Similar to hyaline cartilage but contains both collagen and elastic fibers.

• More flexible and resilient than hyaline cartilage.

• Locations: external ear (auricle) and epiglottis.

Fibrocartilage

• Contains thick collagen fibers, making it the strongest type of cartilage.

• Highly compressible and able to withstand pressure and stretch.

• Locations: menisci of the knee, pubic symphysis, and intervertebral discs.

Growth of Cartilage

Mechanisms of Cartilage Growth

• Appositional growth: Cartilage grows outward by adding new layers to the surface.

• Interstitial growth: Cartilage expands from within as chondrocytes divide and secrete new matrix.

• Cartilage growth typically ends during adolescence as the skeleton matures.

Functions of Bones

Major Roles of Bone Tissue

• Support and Protection: Bones form the framework of the body and protect vital organs (e.g., skull protects the brain, rib cage protects thoracic organs).

• Anchorage and Movement: Skeletal muscles attach to bones via tendons, enabling movement.

• Mineral and Growth Factor Storage: Bones store minerals such as calcium and phosphate, releasing them as needed for physiological processes.

• Blood Cell Formation (Hematopoiesis): Occurs in red marrow cavities, producing red and white blood cells and platelets.

• Fat and Hormone Storage: Yellow marrow stores triglycerides (fat), and bone tissue produces hormones such as osteocalcin, which regulates insulin, glucose, and metabolism.

Example: Clinical Relevance

• Disorders such as osteoporosis (loss of bone density) and rickets (impaired mineralization in children) highlight the importance of bone function in health.