Cartilages are the specialized type of connective tissue composed of cells & extracellular matrix (fibers & ground substances).
• It is devoid of blood vessels, & nerve supply.
Thus, the healing of cartilage is quite slow.
Peculiarities of cartilage• Devoid of nerve supply• Avascular, get nutrition from blood vessels of adjacent tissues by diffusion.• Matrix is not calcified like in bone.
• Chondroblasts (immature)
• Chondrocytes (mature)
|* Chondroblasts → responsible for synthesis of extracellular matrix.
|2) Extracellular matrix
• Ground substance
Mainly composed of
- Glycosaminoglycans (GAG)
- Water & electrolyte
|• Fibers (collagen & elastic fiber)
Fibrocartilage & Hyaline
→ Type-II collagen fibers
Functions of cartilage
• Supports the soft tissues of the body
• Shock absorber
• Sliding area for joints & facilitates bone movements.
• Growth & developments of long bones before & after birth.
Types of cartilage:
- Hyaline cartilage
- Elastic cartilage
Distribution of cartilage:
|• Articular cartilage (cartilage around articular surface of bone)
|• Costal cartilage of ribs which articulate with the sternum
|• Thyroid & cricoid cartilage of larynx
|• Epiphyseal plate of Growing long bone
|• In the walls respiratory tract i.e nose, larynx, trachea, bronchi
|• Annulus fibrosis of intervertebral disc
|• Symphysis pubis
|• Menisci (present in knee joint)
|• Glenoid labrum (of shoulder joint socket)
|• Acetabular labrum of the hip joint socket
|• Articular discs of temporomandibular joint & wrist joint
|• Auricles or pinna of external ear
|• Cartilaginous part of external auditory canal
|• Auditory tube (Eustachian tube)
|• Epiglottis, cuneiform & corniculate cartilage of larynx
It is the fibrocartilagenous structure, intervening between the articular surfaces in synovial joints.
• Temporo-mandibular joint (TMJ)
• Wrist Joint (Radio-carpel joint)
• Sternoclavicular joint
|* Articular discs present in the wrist joint (radio-carpel joint) prevent ulna for making wrist joint.
|* Articular discs of the Temporomandibular joint divide the joint cavity into two compartments.
It is a special type of hyaline cartilage that covers the articular surfaces of the bones of most synovial joints.
• In some cases, where the bone is ossified in membrane, the cartilage is fibrocartilage
• Absence of perichondrium in articular cartilage
• Acts as shock absorbers & ensures gliding movement
The two adjacent vertebral bodies are united to each other by a special type of connective tissue called an intervertebral disc.
• Annulus fibrosus (outer layer of fibrocartilage)
• Nucleus pulposus (inner mass of gelatinous materials, rich in hyaluronic acid)
1. Allow certain movements between the vertebrae.
2. Acts as a shock absorber.
3. Protect the friction of the corresponding vertebrae.
|• Annulus fibrosus, a type of fibrocartilage developed from mesenchyme.
• Nucleus pulposus developed from notochord.
Nucleus pulposus represents notochord.
Dislocation or herniation of intervertebral disc from its position between the vertebrae.
• Due to a reduction in proteoglycan size within the nucleus pulposus diminishes its viscoelasticity leading to focal damage.
• Most common at L 4 & L 5 due to increased mechanical forces across this area.
Just to know:
Mode of nutrition of cartilage:
• Cartilage is devoid of blood vessels
• Hyaline cartilage cells metabolize glucose mainly by anaerobic glycolysis to produce lactic acid.
• Hyaline & elastic cartilage → From vessels of perichondrium
• Fibrocartilage → From blood vessels of surrounding connective tissue
• Articular cartilage → From synovial fluid
Histology of Elastic cartilage: -
• Yellowish in appearance due to the presence of elastic fibers.
• Composed of-
• Chondrocytes are present in the space called lacunae.• Perichondrium present• Elastic fibers form branching & anastomosing network• It's composition is similar to hyaline cartilage except that it contains elastic fibers instead of collagen type-II fibers.
• Chondrocytes &
|2. Extracellular matrix
• Fibers- Elastic fiber
• Ground substance
Histology of fibrocartilage:
• Fibrocartilage is a tissue intermediate between dense connective tissue & hyaline cartilage.
• Cells lies in rows between collagen fiber bundles
• Long, parallel, wavy bundle of collagen fibers present
• No distinct perichondrium
Histology of Hyaline Cartilage
• Weakest cartilage of all
• Matrix around the cells → deeply stained called as territorial matrix.
• Inter-territorial matrix (lightly stained) → present between two groups of cells
• Chondrocytes lie in space called lacunae forming groups of cells called isogenous aggregates.
• Composed of-
• Perichondrium present• Chondrocytes appear in the space called lacunae.
|Cells → Chondrocytes & Chondroblast
|Fibers → Type-II collagen fibers
A lacunae contains either single cells or multiple cells.
Collection of lacunae group of cells called isogenous aggregates.
|• Chondrocytes synthesize collagens & the other matrix molecules.
|* Hyaline & Fibrocartilage contain Type-II type of collagen fibers but elastic cartilage contains elastic fibers.
|* Perichondrium is absent in articular cartilage & Fibrocartilage.
• Its a sheath of dense connective tissue that surrounds the cartilage.
• Not found in articular cartilage & fibrocartilage
Two layers present
Composed of Type-I collagen fibers, fibroblasts & chondrocytes in inner layers.
|Outer fibrous layer (Vascular)
|Inner chondrogenic layer (Cellular)
• It harbors the vascular supply for avascular cartilage.
• Cells around the Perichondrium has the capacity to regenerate to some extent in case of cartilage damage.
• It contains nerves & lymphatic vessels.
Cartilage Formation/ Chondrogenesis:
|• All cartilage derived from the embryonic mesenchyme.
|• The mitotic proliferation of mesenchymal cells occurs which later differentiate into chondroblasts
|• Chondroblasts secrete the components of extracellular matrix & form lacunae and become chondrocytes.
|• Chondrocytes divide one or two times within lacunae to form isogenic groups.
|• Each chondrocytes secrete their own matrix causing it to form its own lacunae and separate apart.
|• The superficial mesenchyme develops into the Perichondrium.
• Synthesis of matrix contributes greatly to the growth of the cartilage.