Ch 7 Cartilage

Cartilage

• An avascular tissue composed of Chondrocytes and an extensive extracellular matrix

• Specialized form of fibrous connective tissue

• 95% of cartilage volume is ECM the chondrocytes are sparse but essential for maintaining the matrix

Chondrocytes

Embedded in ECM. (Contained in matrix cavities called lacunae: fill in vivo but cells shrink in prep

Functions

• support soft tissues

• Guides the development & growth of long bones

The ratio of GAGs to type II collagen fibers

Allows diffusion of the substances in the blood with the surrounding connective tissue and Chondrocytes in the matrix

Classified into 3 types

Hyaline cartilage, elastic cartilage, fibrocartilage

Hyaline cartilage

Characterized by matrix containing type II collagen fiber, GAG (glycosaminoglycans), Proteoglycans and multiadhesive glycoproteins

Elastic cartilage

Elastic fibers and elastic lamellae in addition to the matrix material of hyaline cartilage

Fibrocartilage

Abundant type I collagen fibers in addition to the matrix material of hyaline cartilage

Hyaline cartilage location

• fetal skeletal tissue

• Epiphyseal plates

• rib cage

• Nasal cavity

• Larynx

• Rings of trachea

Elastic cartilage location

• pinna of external ear

• Auditory tube

• Cartilages of larynx (epiglottis)

Fibrocartilage

• intervertebral disks

• Symphysis pubis

• Menisci (knee joint)

Hyaline cartilage function

• resistant to compression

• Provides cushioning

• Support respiratory system

Elastic cartilage function

• provides flexible support

Fibrocartilage

• resists deformation under stress

Hyaline cartilage (presence of Perichondrium)

• YES (except Articular cartilage and Epiphyseal plates)

Elastic cartilage (presence of Perichondrium)

• YES

Fibrocartilage (presence of Perichondrium)

• NO

Hyaline cartilage (undergoes calcification)

• YES

Elastic cartilage (undergoes calcification)

• NO

Fibrocartilage (undergoes calcification)

• YES

Hyaline cartilage (cell types present)

• Chondroblasts, chondrocytes

Elastic cartilage (cell types present)

• Chondroblasts, chondrocytes

Fibrocartilage (cell types present)

• Chondrobalsts, fibroblasts

Hyaline cartilage (features of ECM)

• type II collagen fibrils

• Aggrecan (Proteoglycans)

Elastic cartilage (features of ECM)

• type II collagen fibrils

• Elastic fibers

• Aggrecan

Fibrocartilage (features of ECM)

• type I collagen

• Type II collagen

• Proteoglycan monomers: aggrecan (secreted by Chondrocytes and versican) (secreted by fibroblasts)

Cartilage is

Similar to bone in that the cells are embedded in a matrix that is reinforced with collagen

BUT:

1. Cartilage matrix is not calcified

2. Cartilage is avascular

3. Turnover of matrix (as seen in bone) does not occur

The Perichondrium

Is analogous to the periosteum of bone and covers the surface of cartilage

Chondronectin

Structural glycoprotein that mediates adherence of chondrocytes to ECM

Territorial matrix

Area surrounding chondrocyte; decreased collagen present; stains darker than remainder of matrix

Hyaline cartilage is

The most common type of cartilage and is found on the articulating surface of long bones

Residual cartilage at the proximal and distal end of the bone serves as growth sites called

Epiphyseal growth plates (Epiphyseal discs)

In fully grown individuals, a remnant of cartilage from developing skeleton is found on the

Articular surface joints (ARTICULAR CARTILAGE) and in the rib cage (COSTAL CARTILAGES)

New bone matrix is deposited by

Osteoblasts

Onto the calcified cartilage thereby forming cancellous bone

In adults, hyaline cartilage present in the skeletal unit in the

Trachea, bronchi, larynx, and nose

Hyaline cartilage that covers the Articular surfaces of movable joints is termed

Articular cartilage

Growth of cartilage (interstitial)

From preexisting Chondrocytes

• occurs only by early phases of cartilage formation and within Epiphyseal plates of long bones and in Articular cartilage

Growth of cartilage (appositional)

Differentiation of peripheral cells

• matrix synthesis contributes to growth

• Poor regeneration; in extreme damage, usually forms scar from Perichondrium rather than forming new tissue

Elastic cartilage is surrounded by Perichondrium and unlike hyaline elastic

DOES NOT calcify with age