Cartilage

Question 1

What is Cartilage?

Answer 1

• Semi-rigid connective tissue

* Avascular and aneural (nutrients via diffusion)

Question 2

Function of Cartilage

Answer 2

Forms the supportive framework of some organs

Lines the articulating surfaces of bones

Shock absorption

Makes up the majority of the fetal/immature skeleton (replaced by bone via endochondral ossification)

Question 3

Contents of Cartilage

Answer 3

• Matrix contains proteoglycans

-GAGs are mostly hyaluronic acid, chrondroitin-4-sulfate, and chondroitin-6-sulfate

• Fibers and cells are embedded in the matrix

- Fibers: just collagenous OR collagenous + elastic (depending on type of cartilage)    - Cells: chondrocytes, chondroblasts, chondrogenic cells, fibroblasts

Question 4

Types of Cartilage

Answer 4

o Hyaline cartilage:

• Articular surfaces of long bones, costal cartilage, larynx, trachea, and bronchi
• all synovial joints are lined with hyaline cartilage

o Elastic cartilage
-External, Eustachian tube, and Epiglottis

o Fibrocartilage
- Intervertebral discs, pubic symphysis, TMJ

Question 5

Hyaline Cartilage

Answer 5

• Most common of the 3 types of cartilage
• involved in ENDOCHONDRAL OSSIFICATION
• Matrix looks smooth and glassy
• TYPE II COLLAGEN

-Matrix directly surrounding each chondrocyte is rich in GAGs (basophilic, stains metachromatically)

Question 6

Hyaline Cartilage Matrix

Answer 6

o Collagen embedded in a gel of proteoglycans and glycoproteins
- Proteoglycans (containing GAGs: chondritin 4-sulfate,
chrondritin 6-sulfate, and keratan sulfate) associate with
hyaluronic acid to form aggregates that interact with
collagen

• Water binds to GAGs – allows cartilage to act as a shock absorber (cartilage is 60-80% water)
• Chondronectin (glycoprotein) binds to GAGs and collagen to attach chondrocytes to the matrix

Question 7

Perchondrium

Answer 7

Surrounds the hyaline cartilage except for at the articular cartilage of joints

Made of dense connective tissue – contains fibroblasts and type I collagen
HAS BLOOD VESSELS so diffusion occurs through here to get to the true cartilage

Two layers:
1) Outer fibrous layer (mostly fibroblasts and collagen)

2) Inner chondrogenic layer (chondroblasts and chondrogenic cells)

Chondrogenic cells are PRECURSOR cells that will eventually become cartilage cells

Question 8

Hyaline Cartilage - Cells

Answer 8

o CHRONDROGENIC cells (immature cartilage cells not surrounded by matrix) in inner layer of perichondrium form CHONDROBLASTS, which secrete matrix

o As chondroblasts become surrounded by matrix (GAGs, hyaurlonic acid, etc.) they become trapped in LACUNAE, and are referred to as CHONDROCYTES

o Chondrocytes are flattened near the periphery of cartilage;
round/oval at interior; they are still in an active form but they are just more mature and surrounded by matrix in comparison to chondroblasts
- Found in groups
- Synthesize collagen and other matrix molecules

Question 9

Lacunae

Answer 9

spaces in the matrix where chondrocytes are located; visible when cells shrink during histological preparation

Question 10

Isogenous Group

Answer 10

group of up to 8 cells resulting from mitotic

divisions of a single chondrocyte

Question 11

Types of Matrix in Hyaline Cartilage

Answer 11

o CAPSULAR MATRIX: (around each individual cell) matrix adjacent to a chondrocyte
- Poor in collagen, rich in GAGs (basophilic,metachromatic, PAS-positive)

o TERRITORIAL MATRIX: (around the group) matrix around an isogenous group; more basophilic

o INTERTERRITORIAL MATRIX:
(between the groups) matrix between isogenous groups; more acidophilic

Question 12

Elastic Cartilage

Answer 12

• Found in:
o External ear
o Eustachian tube
o Epiglottis

• Similar to hyaline cartilage
    o Has a perichondrium
    o Chondrocytes, often in 
       isogenous groups, are 
       found in lacunae
     o Type II collagen fibrils in 
        matrix

• Elastic fibers in matrix
o Give the cartilage elasticity
o Can see elastic fibers with special stains
o Without elastic stains, it will look like hyaline cartilage

Question 13

Fibrocartilage

Answer 13

• Found in:
o Intervertebral discs
o Pubic symphysis

• Intermediate between dense connective tissue and hyaline cartilage

o No perichondrium (gradual transition to dense CT)
o Type II and type I collagen    o Matrix is acidophilic due to the type I collagen

o Type I collagen provides increased tensile strength

• Chondrocytes, in their lacunae, are found in parallel rows, separated by
type I collagen fibers

Question 14

How does cartilage develop?

Answer 14

MESODERM&raquo_space;> MESENCHYME&raquo_space;> CHONDROBLASTS&raquo_space;> CHONDROCYTES

(A) The mesenchyme is the precursor tissue of all types of cartilage

(B) Mitotic proliferation of mesenchymal cells gives rise to a highly cellular tissue

(C) Chondroblasts are separated from one another by the formation of a great amount of matrix

(D) Multiplication of cartilage cells gives rise to isogenous groups,each surrounded by a condensation of territorial (capsular matrix)

Question 15

Two Methods of Cartilage Growth

Answer 15

o INTERSTITIAL GROWTH: mitotic division of pre-existing
chondrocytes
- Chondrocytes divide (isogenous groups)
- New matrix expands cartilage from within
- Growth from INSIDE

o APPOSITIONAL GROWTH: differentiation of cells from
chondrogenic layer of perichondrium
- Chondroblasts become chondrocytes when they become embedded in the matrix they produce
- Growth from OUTSIDE