Introduction to Cartilage Tissue

• Cartilage is a specialized connective tissue

Learning Objectives

• Define the general specifications of cartilage tissue.
• Understand the cells and matrix of cartilage.
• Know the classification of cartilage, including hyaline, elastic, and fibrous types

Introduction to Cartilage

• Mesenchyme is the source of cartilage
• Cell and intercellular substances make up cartilage
• Fibers and matrix form the intercellular substance
• Chondroblasts and chondrocytes are the components of cells
• Collagen and elastic fibers are the components of fiber
• Chondro (-cyte & -blast) are located in lacunae, which are isolated small cavities
• Dense connective tissue, called the perichondrium, covers the cartilage

Functions of Cartilage Tissue

• Cartilage is a specialized connective tissue with a firm extracellular matrix
• Cartilage protects against mechanical stress without permanent distortion
• The tissue supports soft tissues
• It acts as a shock absorber because of its elasticity
• The smooth surface allows sliding against joints
• Bone growth relies on cartilage

General Specifications of Cartilage

• Cartilage tissue is a specialized connective tissue type
• A large amount of extracellular matrix is present, composed of collagen and elastic fibers
• A ground substance abundant in proteoglycans exists
• Chondrocytes are a kind of specialized cell that it contains
• Cartilage lacks blood vessels, unlike other connective tissues
• Chondrocytes receive nutrients through diffusion
• Cartilage grows and repairs more slowly than other connective tissues

Cartilage Growth Mechanism

• Cartilage grows in two ways simultaneously: interstitial and appositional

Interstitial Growth

• During immature cartilage development this occurs
• Chondrocytes are capable of mitosis and matrix formation
• Cartilage growth occurs because of this
• Chondrocytes cluster in the tissue, forming isogenous groups

Appositional (Exogenous) Growth

• Mesenchymal cells surround cartilage in the deep perichondrium (or chondrogenic layer)
• Mesenchymal chondrogenic layers separate into chondroblasts
• New chondroblasts derive from chondrogenic
• Additional matrix is formed on the cartilage periphery because they produce supplementary matrix
• Mature cartilage and bones can be created this way

Cells of Cartilage

• Mesenchymal cells give rise to chondroblasts
• Cartilage grows as a result of chondroblast proliferation
• Differentiated mature cartilage cells are termed chondrocytes
• Lacunae are defined as chondrocytes located in tiny isolated matrix cavities

Matrix of Cartilage

• The ground substance is rich in proteoglycans, which consist of a core protein and numerous glycosaminoglycans (GAGs)
• Chondroitin and keratan sulfate are included
• Type I and II collagen fibers are in the matrix
• Type II collagen mainly occurs in cartilage tissue
• Type I collagen is found in fibrocartilage, while Type II collagen is found in hyaline and elastic cartilage

Territorial and Interterritorial Matrix

• The matrix near isogenous chondrocyte groups contains larger amounts and different types of glycosaminoglycans
• This matrix is considered territorial
• The matrix that occupies spaces between chondrocytes is interterritorial

Classification of Cartilage

• Three types of cartilage exist: hyaline, elastic, and fibrocartilage

Hyaline Cartilage Description

• It features a blush-white, shiny ground substance with fine, pale type II collagen fibers
• Numerous isogenous groups can be found
• It provides a smooth surface with flexible, supportive movement at joints

Hyaline Cartilage Location

• It can be found in the trachea
• It can be found in the larynx
• It can be found at the nose tip
• It can be found connecting ribs
• Bone ends join where they appear
• Hyaline cartilage makes up temporary cartilage during human embryo development

Hyaline Cartilage Matrix

• Soluble collagens and proteoglycans enrich the cartilage's ground substances
• It's type II collagen
• A dense connective tissue called perichondrium surrounds the cartilage

Hyaline Cartilage Cells

• Chondrocytes are located inside lacunae
• Hyaline cartilage is easily distinguished from elastic and fibrocartilage due to its homogeneous (glassy appearance) extracellular matrix (ECM)
• Each chondrocyte of the isogenous group is surrounded by a territorial matrix rich in proteoglycans, but low in collagen fibrils
• Interterritorial matrix is located between numerous isogenous groups of collagen type II fibrils
• In histologic sections, collagen fibers are not visible
• An isogenous group is formed by 5-8 chondrocytes

Hyaline Cartilage Nutrition

• Cartilage is avascular
• No blood vessels directly serve the matrix
• The matrix is nourished and wastes are removed through diffusion
• Macromolecule turnover is slow

Elastic Cartilage Description

• It resembles hyaline cartilage, but has more elastic fibers in its matrix
• It consists of type II collagen fibers
• It allows great flexibility and maintains the shape of a structure
• It supports the external ear (pinna), epiglottis, larynx, and Eustachian tube walls

Elastic Cartilage Matrix

• Fibers are quite visible and more numerous
• Chondrocytes are larger than in hyaline cartilage
• The fibrillar component has a different nature
• It mainly consists of elastic fibers
• Its cartilage can be deformed and returned to shape
• Perichondrium surrounds it

Elastic Cartilage Cells

• Lacunae also contain chondrocytes of elastic cartilage
• Isogenous groups are fewer in cells (with populations between 2-3) than in hyaline cartilage

Fibrocartilage Description

• This cartilage is a combination of dense regular connective tissue and hyaline cartilage
• Due to abundant coarse type I collagen fibers, the matrix is acidophilic
• Its ability can absorb compressive shock
• Intervertebral discs, pubic symphysis, and discs of knee joint are some locations that it exists