Cartilage lecture notes for written and viva examination

 Cartilage lecture notes for written and viva examination

It is a special form of connective tissue composed of chondrocytes and a highly specialized extracellular matrix which designed to support to regions of body that require rigidity and flexibility.

Functions of Cartilages:

• Articular cartilage form smooth surface for movement
• It makes shape of ear, nose
• Act as shock absorber in spine ( intervertebral discs)
• It more flexible than the bone, so it breaks less costal cartilage of thoracic cage, ear , nose
• During development of bone, cartilage forms the initial blueprint of the skeletal system before being replaced by bone (a process called endochondral ossification).
• It form framework for respiratory passage to prevent their collapse.

Components of cartilages:

Cells of cartilage: chondroblasts and chondrocytes

Extracellular matrix:

Fibres : collagen and elastic ( impart tensile strength and elasticity)

Ground substance contain hyaluronic acid , glycosaminoglycans and (chondroitin sulphate, keratan sulphate), glycoproteins (chondronectin).

Types of cartilage: (according to the number of cells and the nature of the matrix)  

1. Hyaline cartilage 2.Elastic cartilage 3. Fibrocartilage

 

Features	Hyaline cartilage	Elastic cartilage	Fibrocartilage
Distribution	Tracheo-bronchial cartilage, costal cartilage of rib and nasal cartilage, most of the laryngeal cartilage	Epiglottis, external ear and ear canal, auditory tube, some laryngeal cartilage( corniculate, cuneiform etc.)	Intervertebral discs and pubic symphysis, articular discs of temporo-mandibular, sternoclavicular joint, menisci of the knee joint
Function	Resistant to compression, provides cushioning and low friction surface for joint , structural support in respiratory system	Provides flexible support	Resist deformation under stress
Presence of perichondrium	Yes (except articular cartilage and epiphyseal plates)	Yes	No
Undergoes  calcification	Yes ( during endochondral bone formation )	No	Yes (during bone repair)
Cell types	Chondroblasts, chondrocytes	Chondroblasts, chondrocytes	Chondrocytes, fibroblasts
Chondrocyte in lacunae	Smaller compare to elastic cartilage arranged in isogenous group (2-8)	Larger compare to hyaline  cartilage and closely packed and arranged in isogenous group (2-4)	Small arrange in row parallel to bundles of collagen fibers
Extracellular matrix	Type II collagen fibrils Homogenous and basophilic	Type II collagen fibrils and elastic fibers	Type II & type I collagen fibers Eosinophilic
Slide identification	*Cartilaginous matrix: is homogeneous *Cells: Lacunae (ovoid space within the matrix) contain chondrocyte singly or isogenous groups *Perichondrium: surround the cartilage (if present within the slide then add this points)	*Cartilage matrix contain elastic fiber so it is not homogenous Lacunae (ovoid space within the matrix) contain chondrocyte singly or isogenous groups *Perichondrium surround the cartilage (if present within the slide then add this points)	Cartilaginous matrix: thick collagen fibres located between parallel rows of condrocytes *Cells: the chondrocytes are smaller than those of hyaline or elastic cartilage and they are arranged in  parallel rows between the bundles of  thick collagen fibers *Perichondrium: absent

 

Peculiarities of the cartilage:

1. Cartilages lack blood vessels, lymphatics and nerves.
2. Cartilage has a limited ability to heal and regenerate, primarily because of its avascular nature.
3. when matrix calcified the chondrocytes are die
4. cartilage cells grow by appositional and interstitial methods
5. Cartilages are supplied by diffusion of oxygen and nutrients through extracellular matrix from blood vessels in perichondrium /surrounding tissues/synovial fluid.
6. Extracellular matrix of cartilages is highly permeable.
7. Cartilages are usually surrounded by perichondrium (except articular cartilage and fibrocartilage)

Perichonrium

 it is a connective tissue membrane  that surrounds the hyaline and elastic cartilages.

         It has

(a)  An outer fibrous layer, is composed mostly of fibroblasts and collagen fibers, &

blood vessels  

(b)  A inner cellular or chondrogenic layer, is composed of chondroblast and   chondrogenic cells.

 This   layer helps in growth and repair of cartilage.

Cartilage which are covered by perichondrium:

1.     Hyaline cartilage (except hyaline cartilage of articular surfaces of a  joint, epiphyseal cartilage)

2.     Elastic cartilage

The characteristic features of Chondroblasts and chondrocytes

Chondrocytes and chondroblasts  are derived from mesenchymal cells.

Features of Chondroblasts

1. Immature and young cells of cartilage
2. Shape : oval shape with few processes
3. Location : Chondroblasts are typically found in the perichondrium, a layer of connective tissue surrounding most types of cartilage (excluding articular cartilage, fibrocartilage)
4. Chondroblasts are responsible for producing the extracellular matrix (ECM) of cartilage, which includes collagen fibers and proteoglycans
5. Chondroblasts are precursor cells that can differentiate into chondrocytes, the mature cells of cartilage
6. Chondroblasts contain a high density of organelles, such as the rough endoplasmic reticulum and Golgi apparatus, which are essential for the synthesis and secretion of proteins and other components of the extracellular matrix.
7. Chondroblasts play a central role in both appositional growth (growth in width) and interstitial growth (growth in length) of cartilage.

 

Features of chondrocytes

1. older and mature cells
2. Shape : rounded or spherical shape in the center part of cartilage and oval at the periphery
3. Location : Chondrocytes are found within small cavities called lacunae in the extracellular matrix (ECM) of cartilage singly or in isogenous groups..
4. Chondrocytes generally have a low rate of cell division and mitotic activity, contributing to the limited regenerative capacity of cartilage tissue.
5. Chondrocytes can sense changes in mechanical stress and respond by altering their production of extracellular matrix components.
6. Chondrocytes typically function in a low-oxygen environment because cartilage is avascular (lacks blood vessels).
7. Chondrocytes have some rough endoplasmic reticulum,golgi Apparatus, Lysosome which are involved in the degradation of cellular waste and  mitochondria, which provide energy for cellular activities, primarily through anaerobic metabolism due to the low oxygen environment of cartilage.

Growth of  cartilage

      Cartilage grows by two methods:

 

Interstitial growth: In this type of growth, newly generated chondrocytes deposit extracellular matrix while existing chondrocytes divide mitotically to produce new cartilage.

Appositional growth: The inner layer of perichondrium cells, also known as chondrogenic cells, divide and develop into chondroblasts during a process known as apogephalic growth. The matrix and freshly produced cells are introduced at the surface and periphery.

 

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

For more anatomy topics and video please visit :

My youtube channel : https://www.youtube.com/c/easyhumanatomy73

My website: www.easyhumananatomy.com

My fb page : https://www.facebook.com/easyhumanatomy/