Lecture Notes: Introduction to Skeletal System and Cartilage

Overview

• Focus on the skeletal system as a whole, not just bones.
• Importance of cartilage in bone formation.
• Cartilage as part of the skeletal system contributing to articulations (joints).

Components of the Skeletal System

• Cartilage: Key to articulations (joints) where bones meet.
• Bone Stem Cells: Contribute to various cells like leukocytes and erythrocytes.
• Nervous Tissue: Included as part of the skeletal system.
• Development: Newborns have cartilage (e.g., fontanelles in skull) that hardens into bone.
• Dynamic Nature: Skeleton changes throughout life; stress impacts bone replacement rates.

Types of Cartilage

• Hyaline Cartilage:
  • Least fibers, weak, serves as a template for bone.
  • Found in fetal skeleton, articulating bone ends, trachea, larynx, and nose.
• Elastic Cartilage:
  • Contains elastic fibers, very flexible.
  • Found in external ear and epiglottis.
• Fibrocartilage:
  • Contains many collagen fibers, very strong.
  • Found in intervertebral discs, pubic symphysis, and knee menisci.
  • No perichondrium due to high stress areas.

Cartilage Cells

• Chondrocytes: Resting cartilage cells, not actively making cartilage.
• Chondroblasts: Actively making cartilage.
• Chondrocytes can become chondroblasts when they start making cartilage again.
• Lacunae: Spaces that house chondrocytes; chondroblasts create lacunae as they build cartilage.

Cartilage Properties

• Semi-rigid Connective Tissue: Rigidity depends on type.
• Avascular: Relies on diffusion for nutrient supply.
• Flexibility: Allows for flexibility where needed, less hard than bone.

Cartilage Growth

• Interstitial Growth (Length):

  • Chondrocytes divide through mitosis to chondroblasts.
  • Chondroblasts lay down new cartilage, increasing length.
  • Process: Chondrocytes -> Mitosis -> Chondroblasts -> Lay down cartilage -> Become chondrocytes again.

• Appositional Growth (Width):

  • Stem cells on periphery divide and differentiate into chondroblasts.
  • Chondroblasts lay down new cartilage, increasing width.
  • Process: Stem cells -> Mitosis -> Chondroblasts -> Lay down cartilage -> Become chondrocytes.

Functions of Cartilage

• Supporting Soft Tissues: e.g., trachea.
• Articulations: Cushioning in joints (e.g., hyaline cartilage in articulating bones).
• Bone Growth Precursor: Some bones form using cartilage as a framework.

Conclusion

• Understanding cartilage is crucial for understanding bone growth.
• Concepts of cartilage growth apply to certain types of bone growth.
• Reminder to revisit these concepts during bone-related lectures.