Cartilage:
Cartilage is a
connective tissue as
1) It has
a supportive and protective role as part of the skeletal
system.
2) It is
of mesenchymal origin
3) It is
precursor of bone formation in endochondral
ossification
4) The
cells are widely spaced apart in the ECM
There are
chondroblasts, chondrocytes and lacuna in cartilage. ECM and
periochondrium too.
Cartilage matrix
consists of ECM made up of water, cells, proteoglycan aggregates.
Cartilage has no nerves, lympatics or blood vessels. They consists
of different type of fibres:
1)
hyaline cartilage, type2 cartilage. Most common type of
cartilage. Found on the surface of epiphysis of bones, cartilage
rings, parts of the larynx and precursor of bone in developing
bone. Perichondrium is dense irregular connective
tissue.
2)
Elastic cartilage, elastic fibres
3)
Fibrocartilage, mix of type 1 and 2, mainly type
1.
Cartilage
surrounded by perichondrium.
Appositional
growth: growth from the edges of the cartilage. Cartilage
surrounded by perichondrium, consisting of an inner chondrogenic
layer and an outer fibrous layer. The cells of the chondrogenic
layer can differentiate into chondroblasts and secrete cartilage
ECM.
Intersitial growth:
Growth from within tissue. Chondroblasts form centres of
chondrogensis. The chondroblasts secrete ECM and become surrounded
by it. The chondroblasts divide so each cell occupy a lacuna and
form an isogenous group. As they divide again, they separate,
causing growth of cartilage mass.
Elastic
cartilage:
Similar appearance
to hyaline cartilage. Can tell them apart by staining with orcien
stain. Chrondrocytes are more closely packed with fewer isogenous
groups. Has a perchondrium and can undergo interstitial and
appositional growth. Found in ear and epiglottis.
Fibrocartilage: Has
mainly type 1 collagen. Is strong and incompressible and still give
it some cushioning effect. Examples are intervertebral discs of the
vertebrae column, pubic symphysis and meniscus. It originates from
dense connective tissue. Mix between hyaline cartilage and dense
connective tissue.
‘
Cartilage repair:
Limited ability to repair, best when perichondrium is present. No
blood vessels and lymphatics. Cartilage often replaced by dense
connective tissue and it frequently ossifies in older
people.