Bones and Skeletal Tissues: Structure, Types, and Classification

Bones and Skeletal Tissues

Introduction

The skeletal system provides the framework for the human body, supporting movement, protecting organs, and serving as a reservoir for minerals. Skeletal tissues include bone and cartilage, each with distinct structures and functions essential for anatomy and physiology.

Cartilage: Basic Structure, Types, and Functions

Structure of Skeletal Cartilage

• Cartilage is a resilient, flexible connective tissue found in various parts of the skeleton.

• It contains a high percentage of water, which lends resiliency and flexibility.

• Cartilage is avascular (contains no blood vessels) and aneural (contains no nerves).

• The perichondrium is a dense connective tissue girdle that surrounds cartilage, providing nutrients via blood vessels and resisting outward expansion.

Types of Skeletal Cartilages

Cartilage is classified based on the composition of its extracellular matrix and its location in the body.

• Hyaline Cartilage

  • Provides support, flexibility, and resilience.

  • Contains fine collagen fibers only; most abundant type.

  • Locations: articular (joint) cartilage, costal (rib) cartilage, respiratory tract, and nasal cartilage.

• Elastic Cartilage

  • Similar to hyaline cartilage but contains more elastic fibers.

  • Locations: external ear and epiglottis.

• Fibrocartilage

  • Contains thick collagen fibers, providing great tensile strength.

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

Functions of Cartilage

• Provides support and flexibility to skeletal structures.

• Reduces friction and absorbs shock in joints.

• Serves as a template for bone formation during development.

Classification of Bones

Overview

The adult human skeleton consists of 206 named bones, which are classified into two major groups based on their location and function.

Axial Skeleton

• Forms the long axis of the body.

• Includes the skull, vertebral column, and rib cage.

• Functions: supports and protects the brain, spinal cord, and thoracic organs.

Appendicular Skeleton

• Composed of bones of the upper and lower limbs.

• Includes girdles (pectoral and pelvic) that attach limbs to the axial skeleton.

• Functions: enables movement and manipulation of the environment.

Table: Types of Skeletal Cartilage and Locations

Type of Cartilage	Main Features	Locations
Hyaline	Support, flexibility, fine collagen fibers	Articular cartilage of joints, costal cartilage, respiratory tract, nasal cartilage
Elastic	More elastic fibers, flexible	External ear, epiglottis
Fibrocartilage	Thick collagen fibers, tensile strength	Menisci of knee, intervertebral discs, pubic symphysis

Key Terms

• Perichondrium: Dense connective tissue surrounding cartilage, providing nutrients and structural support.

• Chondrocytes: Mature cartilage cells located in spaces called lacunae.

• Axial Skeleton: Central part of the skeleton including the skull, vertebral column, and rib cage.

• Appendicular Skeleton: Peripheral part of the skeleton including limbs and girdles.

Example: Clinical Application

• Damage to articular cartilage in joints can lead to osteoarthritis, a common degenerative joint disease.

• Fibrocartilage in intervertebral discs helps absorb shock and prevent spinal injuries.