The Cartilage

today lecture is about the cartilage, so we talked previously about the connective tissue, the cartilage is a special type of connective tissue and has the extracellular matrix that is condense into fat but flexible material containing cells of chondrocytes that are embedded in this matrix

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 -depend on the diffusion of the nutrients from nearby blood vessels,

2 -you expected it low 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 plorer of lacuna) . the extracellular matrix consist of fibers

and ground substances.

there are three types of cartilage base on variation of the compassion of 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 collagen fiber the fibro cartilage is different its composed mainly of type one collagen fiber

a) the hyaline cartilage:

its located in the articular surfaces of movable joints , in order reduce the fraction at this joint,

its located in largery respiratory passages and the ventral ends of ribs and epiphyseal plate, ( in the epiphyseal plate its responsible longitudinal growth of bones )

so the first constituence of the hyaline cartilage is extracellular matrix which is consist of type two collagen fiber, another component is proteoglycan aggregate such as aggrecan ( Dr said i have mentioned the aggrecan in the proteoglycans in the connective tissue as an example if u remember it)

the proteoglycan aggregate are very large macromolecules composed of proteoglycan and hyaluronic acid, the proteoglycan are none covalently linked by linked the proteins to the hyaluronic acid and you know that the hyaluronic acid is the unique glycosaminoglycans (GAGs) for it's being non-sulphated(it's the only GAGs which is non-

sulphated) .

proteoglycan them self are composed of GAG which are polysaccharide compose of repeating disaccride 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 keratan 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 sides to collagen type two, integrins and GAGs and it's mediating the adherence of chondrocytes to the extracellular

matrix(ECM)

(she is explain now on the figure of macromolecular presentation on the hyaline cartilage )

as u see on the figure the proteoglycan resample 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 )(12:00)this proteoglycan is non-covalently linked to the hyaluronic acid by linking proteins so the proteoglycan with hyaluronic acid is present the proteoglycan aggregate (e.g. the aggregan). and there is interaction between the

proteoglycan aggregate and collagen type two fiber.

Chondrocyte:

so cartilage cells are called chondrocytes and they 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 is immediately surrounding chondrocytes refers the territorial matrix, which has abundant of GAGs and not that much of collagen.

BUT inter territorial matrix which is distant from lacunae its rich of 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 is covered 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 thus cells that can differentiate into chondroblasts which become then chondrocytes .

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 tissue preparation there is shrinking of the ECM that causes the cells to bull

away and become distorte, this way there is lacunae and space between the cell and its lacunae.

when there is group of cells and their lacuna closed from each other and associated the same Chondrocyte, this what we call isogenous group.

*territorial matrix and the GAGs are basophilic .but the collagen is eosinophilic.

there is 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 very located were separately and long differentiation and rounded to produce the chondroblasts to wear the hyaline cartilage

b) the elastic cartilage :

it's very similar to the hyaline cartilage even in the size and the distribution except that it have elastic fibers in the ECM , and it has perichondrium , and its 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 need to 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.

c) the fibro cartilage:

the fibro cartilage is intermediate between the dense connective tissue and hyaline cartilage .

its bond the intervertebral disks ( between the vertebral ), attachment of certain ligaments and in the pubic symphysis .

the fibro cartilage characterise 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) . (its fond pelvic cavity between the two pubic bones don't worry about it we ganna take it later in the gross anatomy )

(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's just isogenous group of chondrocytes

fibro cartilage does not have perichondrium .

Chondrogenesis ( this suffix, genesis: mean formation . chondro: mean

cartilage) so its the process of cartilage formation or by which cartilage is form

*there are 4 main or major stages in chondrogenesis.

Mesenchyme gives rise to all types of cartilages, its type of the embryonic connective tissue that have this mesenchymal cells which are undibranchiate (28:20), this cells give rise to chodrocytes then they divide or multiply and dibranchiate becoming more rounded and larger

forming thus chondroblasts .

the doctor asked if u can see figure (b) what...( someone answer anaphase ) the Dr good :) I like him cause he answer me before I

complete the Q .

after they becoming rounded and becoming chondroblasts they as chondroblasts start secreting the matrix of the cartilage the component of the ECM and they start move apart from each other.

this is a graph of the cartilage, they multiply forming isogenous group and this process called interstitial growth .

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 is mean the chondrocytes inside the cartilage they multiply forming isogenous group then the cells inside the isogenous group start secreting 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

so interstitial growth result from mitotic division of pre existing chondrocytes wherefore the appositional growth result from the

differentiation of the cells in the inner layer .

- Good Luck All and STUDY WELL -

done by : Mohammed AL Esayi ):