Bones and Skeletal Tissues: Structure, Types, and Functions

Bones and Skeletal Tissues

Overview

The skeletal system is composed of bones and various types of cartilage, providing support, protection, and movement for the human body. This chapter introduces the structure, types, and functions of skeletal tissues, focusing on cartilage and bone.

Cartilage

Location and Basic Structure of Cartilages

• Cartilage is a specialized connective tissue found throughout the adult body.

• Major locations include:

  • External ear

  • Nose

  • Articular cartilages (at joints) and costal cartilage (connecting ribs to sternum)

  • Larynx and trachea

  • Intervertebral discs, pubic symphysis, and articular discs (such as menisci in the knee)

• Cartilage is avascular (lacks blood vessels) and relies on diffusion for nutrient supply.

Structure of Cartilage

• Perichondrium: A dense layer of connective tissue that surrounds most cartilages.

  • Resists outward expansion when cartilage is compressed.

  • Functions in the growth and repair of cartilage.

• Cartilage consists primarily of water, making it resilient and able to spring back to its original shape after deformation.

Types of Cartilage: General Features

• All cartilages share some similarities:

  • The main cell type is the chondrocyte, which resides in small spaces called lacunae.

  • The extracellular matrix contains fibers (collagen or elastic) and a jellylike ground substance.

Types of Cartilage: Classification and Properties

• Hyaline Cartilage:

  • Most abundant type of cartilage in the body.

  • Chondrocytes appear spherical under the microscope.

  • Matrix contains only fine collagen fibrils (not visible with light microscopy).

  • Ground substance holds a large amount of water, providing support through flexibility and resilience.

  • Examples: Articular cartilage of joints, costal cartilage, respiratory cartilages, nasal cartilage.

• Elastic Cartilage:

  • Contains many elastic fibers in addition to collagen.

  • Highly flexible and able to tolerate repeated bending.

  • Examples: Epiglottis, cartilage of the external ear.

• Fibrocartilage:

  • Contains thick collagen fibers, making it extremely tough.

  • Resists both strong compression and strong tension (pulling forces).

  • Intermediate in structure between hyaline and elastic cartilage.

  • Examples: Pubic symphysis, menisci of the knee, anulus fibrosus of intervertebral discs.

Comparison of Cartilage Types

Type	Main Fibers	Key Properties	Locations
Hyaline	Fine collagen fibrils	Support, flexibility, resilience	Joints, ribs, nose, respiratory tract
Elastic	Elastic fibers	Flexibility, repeated bending	External ear, epiglottis
Fibrocartilage	Thick collagen fibers	Strong compression and tension resistance	Intervertebral discs, pubic symphysis, menisci

Functions of Cartilage

• Provides support and shape to various body structures.

• Reduces friction and absorbs shock in joints (articular cartilage).

• Forms the template for bone growth in the embryo and during development.

Growth and Repair of Cartilage

• Cartilage grows by two mechanisms:

  • Appositional growth: Chondroblasts in the perichondrium produce new cartilage on the surface, increasing width.

  • Interstitial growth: Chondrocytes within the cartilage divide and secrete new matrix, increasing length.

• Cartilage growth slows and eventually stops when the skeleton reaches maturity.

Additional info: Cartilage is essential for the development and function of the skeletal system, serving as a precursor to bone in the embryo and providing flexible support in adults.