Scheda di revisione: Cartilaginous Tissue

📋 Course Outline

1. Cartilage within connective tissue
2. Cartilage structure and perichondrium
3. Hyaline cartilage
4. Elastic cartilage
5. Fibrocartilage
6. Cartilage growth and functions

📖 1. Cartilage within connective tissue

📝 Essential Points

★ Must-know

• Cartilage is one of the specialized connective tissues alongside bone tissue, blood, and lymph.
• The three types of cartilage are hyaline cartilage, elastic cartilage, and fibrocartilage.

📖 2. Cartilage structure and perichondrium

🔑 Key Concepts & Definitions

• Cartilaginous tissue : Formed by a dense network of collagen and elastic fibres firmly embedded in chondroitin sulphate.
• Perichondrium : A covering of dense irregular connective tissue on the surface of cartilage that is vascularized and innervated.

📝 Essential Points

★ Must-know

• In cartilage, collagen provides strength, elastic fibres provide elasticity, and chondroitin sulphate provides flexibility or resilience.
• The ground substance of cartilage has no blood vessels or nerve endings.

Further detail

• Cartilage contains chondrocytes that are isolated or grouped within spaces called lacunae.
• Perichondrium has an outer fibrous layer with few fibroblasts and an inner chondrogenic layer whose cells form chondroblasts and chondrocytes.
• Cartilage is nourished by diffusion of gaseous metabolites and small molecules from the perichondrium through the ground substance.
• Articular hyaline cartilage obtains nutrients from synovial fluid because it lacks perichondrium.

📖 3. Hyaline cartilage

📝 Essential Points

★ Must-know

• Hyaline cartilage is the most abundant and the weakest type of cartilage.
• Hyaline cartilage usually has perichondrium, except in articular cartilage and epiphyseal plates.
• Hyaline cartilage reduces friction at joints and provides flexibility, support, resilience, and shock absorption.
• Hyaline cartilage is located on :
  • articular surfaces of long bones
  • in the nose
  • larynx
  • trachea
  • bronchi
  • bronchioles
  • ventral ends of ribs
  • and in the skeleton of the embryo
  • foetus

Further detail

• Hyaline cartilage contains fine collagen fibres in a jelly-like bluish-white shiny ground substance, and its chondrocytes lie in lacunae.
• Because hyaline cartilage has no blood vessels or nerves, its repair is very slow.

📖 4. Elastic cartilage

📝 Essential Points

★ Must-know

• Elastic cartilage has an extracellular matrix rich in elastic fibres or elastin.
• Elastic cartilage provides support and elasticity and helps maintain the shape of organs after deformation.
• Elastic cartilage is found in :
  • the ear
  • vocal cartilages
  • and Eustachian tube

Further detail

• Elastic cartilage is covered by perichondrium.
• Elastic cartilage contains a higher amount of cells than the other cartilaginous tissues and does not convert into bone.

📖 5. Fibrocartilage

📝 Essential Points

★ Must-know

• Fibrocartilage contains multiple organized layers or bundles of collagen that give it great strength and allow it to absorb shock.
• Fibrocartilage does not have perichondrium and is linked to dense connective tissue.
• Fibrocartilage is the strongest of the three types of cartilage.
• Fibrocartilage is located in :
  • intervertebral discs
  • menisci
  • and the temporomandibular joint

Further detail

• The main function of fibrocartilage is to provide strength.

📖 6. Cartilage growth and functions

🔑 Key Concepts & Definitions

• Isogenous groups : Lacunae containing **2 to 4 **cells produced by mitotic division during interstitial growth.

📝 Essential Points

★ Must-know

• Most cartilage originates from mesenchyme during chondrogenesis, which begins when chondroprogenitor mesenchymal cells cluster into a dense mass of rounded cells.
• Interstitial growth is the formation of new cartilage inside preexisting cartilage by division of chondrocytes that produce new matrix, and it continues in childhood and adolescence in specific places.
• Appositional growth is the formation of new cartilage on the surface of preexisting cartilage when chondroblasts under the perichondrium secrete matrix, increasing cartilage width, and it continues in adolescence.
• Cartilage has mechanical support functions by resisting tension, compression, and shear, provides structural flexibility and elasticity, forms the embryonic skeleton, and allows longitudinal growth of long bones.

Further detail

• In regions where cartilage is forming, mesenchymal cells gather in chondrification centers, differentiate into chondroblasts, divide, secrete matrix, and become cells in lacunae.
• Cartilage repair and growth are slow processes because cartilage is avascular.

📊 Synthesis Tables

Types of cartilage compared

Type	Perichondrium	Main property	Typical locations
Hyaline cartilage	Present except in articular cartilage and epiphyseal plates	Most abundant, weakest, reduces friction and absorbs shock	Articular surfaces, nose, larynx, trachea, bronchi, bronchioles, ventral ends of ribs, embryo and foetus skeleton
Elastic cartilage	Present	Provides strength and elasticity, maintains shape after deformation	Ear, vocal cartilages, Eustachian tube
Fibrocartilage	Absent	Strongest type, provides strength and absorbs shock	Intervertebral discs, menisci, temporomandibular joint

Cartilage growth mechanisms

Mechanism	Where it occurs	Cells involved	Result
Interstitial growth	Inside preexisting cartilage	Chondrocytes	New matrix forms within cartilage
Appositional growth	Surface under the perichondrium	Chondroblasts from chondrogenic perichondrium	New matrix increases cartilage width

⚠️ Common Pitfalls & Confusions

1. Cartilage belongs to specialized connective tissue, not to connective tissue proper.
2. Fibrocartilage can be confused with dense connective tissue because both are collagen-rich.
3. Cartilaginous tissue should not be confused with bone tissue, whose matrix is mineralized.
4. Elasticity from elastic fibres should not be confused with flexibility from chondroitin sulphate.
5. Lacunae in cartilage can be confused with osteocyte lacunae in bone.
6. Perichondrium is vascularized, but the cartilage matrix itself is avascular and aneural.
7. Perichondrium is absent in fibrocartilage, articular cartilage, and epiphyseal discs.

✅ Exam Checklist

1. Cartilaginous tissue
2. Isogenous groups
3. Perichondrium
4. Cartilage is one of the specialized connective tissues alongside bone tissue, blood, and lymph.
5. In cartilage, collagen provides strength, elastic fibres provide elasticity, and chondroitin sulphate provides flexibility or resilience.
6. Hyaline cartilage is the most abundant and the weakest type of cartilage.
7. Elastic cartilage has an extracellular matrix rich in elastic fibres or elastin.
8. Fibrocartilage contains multiple organized layers or bundles of collagen that give it great strength and allow it to absorb shock.
9. Most cartilage originates from mesenchyme during chondrogenesis, which begins when chondroprogenitor mesenchymal cells cluster into a dense mass
10. The three types of cartilage are hyaline cartilage, elastic cartilage, and fibrocartilage.
11. The ground substance of cartilage has no blood vessels or nerve endings.
12. Hyaline cartilage usually has perichondrium, except in articular cartilage and epiphyseal plates.
13. Elastic cartilage provides support and elasticity and helps maintain the shape of organs after deformation.
14. Fibrocartilage does not have perichondrium and is linked to dense connective tissue.