Cartilage

Learning Objectives

After reading this post you will know:

• What is cartilage (definition)?
• Functions of cartilages.
• Characteristic features of cartilage tissue.
• Components of cartilage.
• Types of cartilage and their sites.
• Differences between hyaline, elastic and fibrous cartilage.

Q. What is cartilage?
A. Cartilage is a specialized connective tissue designed to give support to regions of body that require rigidity and flexibility.

Q. What the functions of cartilages?
A. Functions of Cartilages:

• Form framework for respiratory passage to prevent their collapse.
  
• Act as shock absorber in spine ( intervertebral discs).
• Resist compressive forces at joints ( articular catilages).
• Helps in growth of bone (epiphyseal plate).

Q. What are the characteristic features of Cartilages.
A. Characteristic features of Cartilages:

• Cartilages lack blood vessels, lymphatics and nerves.
• Cartilages are supplied by diffusion of oxygen and nutrients through extracellular matrix from blood vessels in perichondrium /surrounding tissues/synovial fluid.
• Extracellular matrix of cartilages is highly permeable.
• Cartilages have poor regeneration capacity.
• Cartilages are usually surrounded by perichondrium (except articular cartilage and fibrocartilage).

Q.What are the components of cartilages?
A. Components of cartilages:

• Cells are chondroblasts and chondrocytes
• Fibres are collagen and elastic ( impart tensile strength and elasticity)
• Ground substance is made up of hyaluronic acid , glycosaminoglycans and (chondroitin sulphate, keratan sulphate), glycoproteins (chondronectin).

Q. What is perichondrium?
A.   Perichonrium is a connective tissue sheath that surrounds the hyaline and elastic cartilages.

•  It has two layers:
  •  outer fibrous layer  contains collagen fibers, fibroblasts,  blood vessels.
  • Inner chondrogenic layer is cellular. It contains chondrogenic cells and chondroblasts.
•  It helps in growth and repair of cartilage.

Q. What are the characteristic features of Chondroblasts and chondrocytes?
A. Chondrocytes and chondroblasts  are derived from mesenchymal cells.

Chondroblasts are:

• oval shaped young  cells  with cell processes.
• present in perichondrium.
• precursors of  chondrocytes.

Chondrocytes are

• older and mature cells.
• oval shaped and small at the periphery.
• round and large towards the center.
• located within the lacunae, singly or in isogenous groups.

Q.   Differentiate between hyaline, elastic and fibrous cartilage.

A.

Q. How does a cartilage grows?

A. Cartilage grows by two methods:

Interstitial growth:  In this type of growth  the cartilage  grows by mitotic divisions of existing chondrocytes and  deposition of the extracellular matrix  by these newly formed chondrocytes.

Appositional growth:  In this type of growth,  the inner layer of perichondrium cells ( chondrogenic cells) divide and differentiate into chondroblasts. The newly formed cells and matrix are added at the periphery/surface .