Lecture
Dr. Noor Erekat
8
The Cartilage today lecture is about the cartilage, so we talked previously iou sly about about the connective tissue, the cartilage is a special type of connec tive tissue
and has the extracellular matri x that is condense into fat but flexible material containing cells of chondrocytes that that are embedded in this matrix the cartilage is avascular ( its mean no blood vessels) it may ha ve blood vessels that traversed to nourish nourish oth er tissues by passing the cartilage ,
the cartilage also lack of lymphati c 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 , bec ause 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 matri x , the cells as mentioned they are called chondrocytes . they occupied or located in spa ces called l acunae
( lacunae is plorer of la cuna) . the extracellular matri x consist of fibers and ground substan ces . there are three types of cartilage base on variation of the compassion of extracellular matri x : a) hyaline,
b) elastic
c) and fibro cartilage.
the hyaline and elastic cartilage are similar both compose d mainly of type two collagen fibers , but the elastic cartilage has elastic fiber in addition to typ e two collagen fiber the fibro cartilage is diff erent its composed mainly of type one collagen fib 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 bon es )
so the first constituence of the hyaline cartilage is extracellular matri x which is consist of type two collagen fiber, another component is proteoglycan aggr egate such as aggrecan ( Dr said i ha ve mentioned the aggrecan in the prot eoglycans in the connective tissue as an example if u remember it)
the prot eoglycan aggregate are very large m acromolec ules composed of proteoglycan and hyaluroni c acid, the prot eoglycan are none covalently link ed by link ed 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 whi ch is non -sulphated) . proteoglycan them self are composed of GAG which are polysa ccharide compose of repeating disa ccride unit and core-protein thus GAGs ar e covalently link ed .
the main GAG that ar e present in the extracellular matri x of hyaline cartilage are chondroitin 4 -sulpghate and chondroitin 6-sulphate in
addition to k eratan sulphate .
now in addition to this two ( two collagen fibers
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proteoglycan
aggregate ) you have the multi adhesive glycoprotein called chondronectin ( which chondro r ef er to the cartilage ) pres ent in the cartilage , it has binding sid es to collagen typ type two, integrins and GAGs
and it's mediating the adherence of chondrocytes to the extracellular matrix(ECM)
(she is explain now on th e 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 th e stem of the bottel brush and GAG the brest cells of the brush ( so th e prot eoglycan is composed of core protein and GAG atta ched to it )( 12:00)this prot eoglycan is non covalently linked to the hyaluronic acid by linking prot eins so the
proteoglycan with hyaluroni c acid is pr esent the prot eoglycan aggregate (e.g. the aggregan). and there is interaction between the proteoglycan aggregate and an d collagen type two fiber .
Chondrocyte: hondrocyte :
so cartilage cells are called chondrocytes and they occupy spaces in the cartilage called lacunae , chondrocytes f ound 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 produ ce more chondrocytes . the function of the chondrocytes: can be accelerated by ( growth hormon e, thyroxin and t estosterone.)
it can be slowed ( cortisone, hydrocortison e and estradiol ) Cartilage growth depends on pituitary d erived growth hormone somatotropin . the areas which is immediately surrounding chondrocytes ref ers the territorial matrix, which has abundant of GAGs and not that mu ch of collagen. BUT
inter territorial matrix which is distant from la cunae its rich of
collagen. Hyaline cartilage
is invested in dense connective tissue called
perichondrium . its consist mainly of typ e 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 th e cartilage . so the inner layer of perichondrium has thus cells that can diff erentiate into chondroblasts whi ch become then chondrocytes. perichondrium has connective tissue, the fibroblast is main cell in the connective tissue to produce ECM and has nu clei .
the lacunae is circular over the Chondrocyte , remember due to tissue preparation there is shrinking of th e ECM that causes the cells to bull
away and become distorte, this way there is lacunae and spa ce between the cell and its la cunae . when there is group of cells and their la cuna closed from each other and associated the same Chondro cyte, 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 hyalin e cartilage and noti ce there is gradual transition in th e diff erentiation of this fibroblasts , and they are very lo cated were separately and long diff erentiation and round ed to produce the chondroblasts to w ear the hyaline cartilag e
b) the elastic cartilage : it's very similar to th e 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 th e auricle ear, walls of the external auditory canals, the auditory auditory (Eustachian) tubes, epiglottis
and the cuneiform cartilage in the larynx .
this is a ma crograph of th e elastic cartilage, and elastic fiber need to a special stain(Or cein stain) to appear pure under the light microscope, so as u can see in the figure the chondrocytes and the material rial in between should b e the elastic fibers , and u can see the perichondrium which is a dense connec tive tissue, and the lacunae containing the chondro cytes, and ECM .
c) the fibro cartilage : the fibro cartilage is intermediate between the dense connec tive tissue and hyaline cartilage. its bond th e intervertebral disks ( b et ween the vertebral ), attachment of certain ligaments and in th e pubic symphysis . the fibro cartilage chara cteris e by having Chondrocyte containing lacunae that are less numerals and mor e 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 p elvic cavity between the two pubic bones don't worry about it we ganna take it later in the gross anatomy )
(a) is a photo ma crograph of fibro cartilage at low magnification you can see the constituence ECM unlike the hyaline & elastic cartilages, it
has large spaces betwee n chondrocytes , and the chondrocytes line long the axis . and (b) is a photo mi crograph but in high er magnification u can see the chondro cytes with their la cunae and its long arrows and this arrows ar e
further to each other .and it's just isog enous group of chondrocytes fibro cartilage does not ha ve perichondrium . Chondrogenesis ( this suffix, g enesis: m ean formation . chondro: m ean cartilage)
so its the process of cartilage formation or by whi ch cartilage
is form *
there are 4 main or major stag es in chondrogenesis .
Mesenchyme gives rise to all types of cartilages, its type of the embryonic connective tissue that have this mesenchymal cells which
are undibran chiate (28:20), this cells give rise to chodrocytes then they divide or multiply and dibran chiate 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 lik e him cause he answer me before I complete the Q .
after they becoming rounded and becoming chondroblasts th ey as chondroblasts start s ecreting the matrix of the cartilage the component
of the ECM and they start move apart from each other.
this is a graph of th e cartilage, they multiply forming isog enous group and this proce ss called interstitial growth. growth . so variable growth of the cartilage is accomplish ed by two pro cess : 1)
interstitial growth
2) appositional growth
interstitial growth ( int er : between ) so it's from insid e the cartilage to out , this is mean the chondrocytes insid e 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 r esult from the diff erentiation of the cells in the inner layer of the perichondrium so interstitial growth r esult from mitoti c division of pr e existing chondro cytes wherefore the appositional growth r esult from the
diff erentiation of the cells in the inner layer . -
Good Luck All and S TUDY WELL
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done by : Mohammed AL Esayi :)
