8/3/2019 Histo 9 Cartilage

1/9

Lecture # 9 :THE CARTILAGE

Before we move on, lets try to remember what Dr.Kassim has taught in the

previous lecture. In the last lecture Dr. Kassim talked about the connective tissue

and that any connective tissues consists of 3 major elements which are:

1. cells2. fibers3. ground substances ( extracellular matrix)

The cartilage is considered as a special type of connective tissue and accordingly it

also consists of the 3 major elements (cells, fibers, ground substances).

And if you remember in the last lecture. The function of a connective tissue

is to connect tissues together. When it comes to the cartilage which is a special

type of connective tissue, with some modifications, the function of the cartilage is

somewhat different from the general function of the connective tissue.

FUNCTION:

a) Bears the Mechanical stress without permanent distortion.b) Support of Soft tissues.c) A shock absorbantd) Facilitate Joint Movemente) Bone development &growth . (ie: long bones)

The cartilage is avascular ( its mean no blood vessels) it may have blood vessels

that traversed to nourish other tissues by passing the cartilage , the cartilage also

lack of lymphatic vessels and nerves , since the cartilage is avascular so it :

1- depends on the diffusion of the nutrients from nearby blood vessels ,

8/3/2019 Histo 9 Cartilage

2/9

2- low in metabolic rate or activity .

because the cartilage is special kind of connective tissue it has the same

constituency as the connective tissue so the cartilage is compose of cells and

extracellular matrix , the cells as mentioned they are called chondrocytes . they

occupied or located in spaces called lacunae ( lacunae is plural of lacuna) . the

extracellular matrix consist of fibers and ground substances .

:CHONDROCYTES

Chondrocytes occupy spaces in the cartilage called lacunae , chondrocytes

found in small group or clusters- which represent the offspring of a single parent

Chondrocyte , this chodrocytes and the associated lacunae produce the matrix

components and therefore moving the part from each other to occupy separate

lacunae and continue in separating to multiply and produce more chondrocytes .

the function of the chondrocytes:

can be accelerated by ( growth hormone, thyroxin and testosterone.)

it can be slowed ( cortisone, hydrocortisone and estradiol )

Cartilage growth depends on pituitary derived growth hormone somatotropin .

the areas which immediately surrounds the chondrocytes are referred as the

territorial matrix, which has abundant of GAGs and not that much of collagen.

BUT inter territorial matrixwhich is distant from lacunae is rich in collagen.

Hyaline cartilage is invested in dense connective tissue called perichondrium .its

consist mainly of type one collagen fiber and has numerous fibroblasts and it

covers the hyaline cartilage except the articular cartilage.the inner layer of

perichondrium is chondrogenic ( genic: mean have the ability to form ) so

chondrogenic it has the potential to form the cartilage .

so the inner layer of perichondrium has cells that can differentiate into

chondroblasts which becomes chondrocytes.

8/3/2019 Histo 9 Cartilage

3/9

perichondrium has connective tissue, the fibroblast is main cell in the connective

tissue to produce ECM and has nuclei .

the lacunae is circular over the Chondrocyte , remember due to tissues

preparation there is shrinking of the ECM that causes the cells to pull away andbecome distort, this way there is lacunae and space between the cell and its

lacunae .

when there is group of cells and their lacuna is close to each other and

associates the same Chondrocyte, this iscalled an isogenous group.

there is an area called the transitional area between perichondrium and hyaline

cartilage and notice there is gradual transition in the differentiation of this

fibroblasts , and they are located separately . they are also long differentiated

and rounded to produce the chondroblasts .

THE EXTRACELLULAR MATRIX (ECM/GROUND SUBSTANCE):

The ECM is mainly made of water, where water is the most dominant element.

Besides water, it is also made of glycoproteins, glycosaminoglycans(GAGs) and

proteoglycans. The water dominance in the ECM is highly linked to the GAGs as

they have sulphates that highly attracts water. The jelly-like ground substance is due

to the chondroitin sulfate present.

(read the connective tissue tafare3 for detailed explanation on the ECM)

TYPES OF CARTILAGE

there are three types of cartilage base on variation of the compositionof

extracellular matrix :

hyaline, b) elastic c) and fibro cartilage. a)

the hyaline and elastic cartilage are similar both composed mainly of type two

collagen fibers , but the elastic cartilage has elastic fiber in addition to type two

8/3/2019 Histo 9 Cartilage

4/9

collagen fiber.the fibro cartilage is different, it is composed mainly of type one

collagen fiber.

*although the collagen and elastic fibers are flexible, the cartilage tissue is still firm in

consistency.

a) the hyaline cartilage:

it is located in the articular surfaces of movable joints , in order reduce the

friction at this joint ,

it is located in large respiratory passages and the ventral ends of ribs and

epiphyseal plate, ( in the epiphyseal plate its responsible longitudinal growth ofbones )

so the first constituencies of the hyaline cartilage is the extracellular matrix

which consists of type two collagen fiber, another component is proteoglycan

aggregate (such as aggrecan in the connective tissue lecture)

the proteoglycan aggregate are very large macromolecules composed of

proteoglycan and hyaluronic acid, the proteoglycan are none covalently linked

by the proteins to the hyaluronic acid and you know that the hyaluronic acid is a

8/3/2019 Histo 9 Cartilage

5/9

unique glycosaminoglycans (GAGs) for it is non-sulphated(it's the only GAGs

which is non-sulphated) .

proteoglycan them self are composed of GAG which are polysaccharide compose

of repeating disaccharide unit and core-protein thus GAGs are covalently linked.

the main GAG that are present in the extracellular matrix of hyaline cartilage are

chondroitin 4-sulpghate and chondroitin 6-sulphate in addition to keratin

sulphate .

now in addition to this two ( two collagen fibers - proteoglycan aggregate ) you

have the multi adhesive glycoprotein called chondronectin ( which chondro

refer to the cartilage ) present in the cartilage , it has binding sites to collagen

type two, integrins and GAGs and it's mediating the adherence of chondrocytes

to the extracellular matrix(ECM)

as u see on the figure the proteoglycan resamble the battel brush and the core-

protein remind you of the stem of the bottel brush and GAG the brest cells of

the brush ( so the proteoglycan is composed of core-protein and GAG attached

to it)this proteoglycan is non-covalently linked to the hyaluronic acid by linking

proteins so the proteoglycan with hyaluronic acid is present the proteoglycan

8/3/2019 Histo 9 Cartilage

6/9

aggregate and there is interactions between the proteoglycan aggregate and

collagen type two fiber .

b) the elastic cartilage :

it is very similar to the hyaline cartilage even in the size and the distribution

except that it has elastic fibers in the ECM , and it has perichondrium , and it is

located or found in the auricle ear, walls of the external auditory canals, the

auditory (Eustachian) tubes, epiglottis and the cuneiform cartilage in the larynx .

this is a macrograph of the elastic cartilage, and elastic fiber needs a special

stain(Orcein stain) to appear pure under the light microscope, so as u can see in

the figure the chondrocytes and the material in between should be the elastic

fibers , and u can see the perichondrium which is a dense connective tissue, and

the lacunae containing the chondrocytes, and ECM .

8/3/2019 Histo 9 Cartilage

7/9

c) the fibro cartilage :the fibro cartilage is an intermediate between the dense connective tissue and

hyaline cartilage.

it binds the intervertebral disks ( between the vertebral ), attachment of certain

ligaments and in the pubic symphysis .

the fibro cartilage characterizes by having Chondrocyte containing lacunae that

are less numerals and more separated from each other, and this chondrocytes

are a line along the axis of the hyaline cartilage in the axial direction fairly to

each other .

fibro cartilage has abundant collagen type one in its ECM . (be aware, not type

two collagen) . (it is found at pelvic cavity between the two pubic bones )

(a) is a photo macrograph of fibro cartilage at low magnification you can see the

constituence ECM unlike the hyaline & elastic cartilages, it has large spaces

between chondrocytes , and the chondrocytes line long the axis . and (b) is a photo micrograph but in higher magnification u can see the

chondrocytes with their lacunae and its long arrows and this arrows are further

to each other .and it is an isogenous group of chondrocytes

fibro cartilage does not have perichondrium .

8/3/2019 Histo 9 Cartilage

8/9

DEVELOPMENT OF CARTILAGE (CHONDOROGENESIS)

there are 4 main or major stages in chondrogenesis .

1.Mesenchyme gives rise to all types of cartilages, its type of the embryonicconnective tissue that have this mesenchymal cells which are un-dibranchiate

this cells give rise to chondrocytes .

2.then they divide or multiply and dibranchiate becoming more rounded and

larger forming thus chondroblasts .

3.after they become rounded and becomes chondroblasts, there is actin in the

secreting of the matrix which separate the chondoroblasts from each other.(look

at the figure below)

8/3/2019 Histo 9 Cartilage

9/9

4.After the mitotic division of the pre-existing chondrocytes , differentiation starts

( at the centre) in the inner layer.

so variable growth of the cartilage is accomplished by two process :1) interstitial growth 2) appositional growth

interstitial growth ( inter : between ) so it's from inside the cartilage to out , this

means the chondrocytes inside the cartilage they multiply forming isogenous

group then the cells inside the isogenous group start secreting actin in the

matrix causing them to move apart from each other occupying separate lacunae

to start multiply again and again .appositional growth result from the differentiation of the cells in the inner layer

of the perichondrium .

******************************************************************

LET US DO OUR BEST AND LET GOD DO THE REST. GOODLUCK GUYS

DONE BY,

ULYA HUSAMUDIN