Cartilage is a type of connective tissue composed of chondrocytes and ECM. The chondrocytes produce and maintain the matrix.
It has a supportive and protective role as part of skeletal system.
There are different types of cartilage.
It originates from mesenchyme.
Precursor to bone formation in ossification
Avascular and aneural
Composed of ECM, water, GAGs and fibres(Collagen and elastic)
3 types of cartilage, Hyaline, elastic and fibrocartilage
Hyaline cartilage( covers ends of the bones): articular cartilage on bones, no perichondrium on articular cartilage. Hyaline cartilage surrounded by dense irregular connective tissue.(perichondrium). Appositional growthby cells of perichondrium differentiating into chondroblasts and forming new cartilage. Can grow from within too. Avascular
Elastic cartilage: similar but chondrocytes are more closely packed. Fewer isogenous groups.
Elastic fibres predominate in ECM
In intervertebral discs
Mostly collagen fibres
Dense connective tissue
Mix of hayline cartilage and dense connective tissue
From UTAS notes: This is not a comprehensive guide, its my summary
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.
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.