Bones and Skeletal Tissue: Structure, Types, and Functions

Bones and Skeletal Tissue

Introduction

The skeletal system is composed of bones and various types of skeletal tissue, including cartilage. These structures provide support, protection, and facilitate movement in the human body. Understanding the basic structure and types of skeletal tissue is essential for the study of anatomy and physiology.

Cartilage: Basic Structure, Types, and Locations

Skeletal Cartilage

Skeletal cartilage is a specialized connective tissue that plays a crucial role in the development and function of the skeletal system. It is characterized by its resilience, lack of blood vessels and nerves, and its surrounding membrane, the perichondrium.

• Water lends resiliency: The high water content allows cartilage to withstand compression and return to its original shape.

• No blood vessels or nerves: Cartilage is avascular and aneural, which limits its ability to heal after injury.

• Perichondrium: A dense connective tissue girdle that surrounds cartilage, providing nutrients via blood vessels and resisting outward expansion.

Cells and Matrix of Cartilage

• Chondrocytes: The primary cells found in cartilage, residing in small cavities called lacunae.

• Extracellular matrix: The non-cellular component that provides structural support and flexibility.

Types of Skeletal Cartilage

There are three main types of cartilage, each with distinct properties and locations:

• Hyaline cartilage:

  • Provides support, flexibility, and resilience.

  • Contains only collagen fibers; most abundant type.

  • Found in articular (joint), costal (rib), respiratory, and nasal cartilage.

• Elastic cartilage:

  • Similar to hyaline cartilage but contains elastic fibers 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.

Microscopic Structure of Elastic Cartilage

The provided image shows elastic cartilage under the microscope, highlighting the presence of chondrocytes within lacunae. Elastic fibers are not visible in this particular stain but are present in the matrix, contributing to the tissue's flexibility.

Key Features of Elastic Cartilage:

• Chondrocytes are embedded in lacunae.

• Matrix contains elastic fibers (not always visible in standard histological stains).

• Provides flexible support in structures such as the ear and epiglottis.

Summary Table: Types of Cartilage

Type	Main Fibers	Function	Location
Hyaline	Collagen	Support, flexibility, resilience	Articular surfaces, ribs, nose, respiratory tract
Elastic	Elastic & Collagen	Flexible support	External ear, epiglottis
Fibrocartilage	Thick Collagen	Tensile strength	Knee menisci, intervertebral discs

Key Terms and Definitions

• Chondrocyte: A mature cartilage cell found in lacunae.

• Lacunae: Small cavities within the cartilage matrix that house chondrocytes.

• Perichondrium: A layer of dense connective tissue surrounding cartilage, providing nutrients and structural support.

• Extracellular matrix: The non-cellular component of cartilage, composed of fibers and ground substance.

Applications and Clinical Relevance

• Articular cartilage is essential for smooth joint movement and is often damaged in arthritis.

• Elastic cartilage maintains the shape of flexible structures like the ear.

• Fibrocartilage resists compression and tension, crucial in weight-bearing joints.

Additional info: Cartilage growth and repair are limited due to its avascular nature. Damage to cartilage often requires medical intervention, such as surgical repair or transplantation.