Cartilage
Characterized byan extracellular matrix enriched with GAG and proteoglycans.
firm consistency of the extracellular matrix allow the tissues to be mechanical stresses without permanent distortion.
cartilage is essential for the development and growth of long bones before and after birth.
cartilage consists of cells, chondrocytes and chondroblasts
Three types of cartilage : Hyaline cartilage elastic cartilage fibrocartilage
cell nests : are the chondrocytes which found in little clusters , consisting of two or more cells in one lacuna
function of chondrocytes: synthesize and secrete the extracellular matrix, in hyaline cartilage chondrocytes
synthesize type II collage, proteoglycan, hyaluronic acid and chondroitin
perichondrium: is essential for the growth and maintenance of cartilage , it is rich in collagen type I fibers and contains numerous fibroblasts. The cells in the inner layer of the perichondrium are chondroblasts.
Collagen , hyaloronic acid , proteoglycans and small amount of several glycoproteins are the principal macromolecules present in all types of cartilage matrix .
Embryology of Cartilage: HYPERLINK "http://www.courseweb.uottawa.ca/medicine-histology/english/musculoskeletal/default.htm" \l "Histology"
Cartilage arises from mesenchyme. Some mesenchyme cells aggregate to form a blastema. The cells of the blastema begin to secrete cartilage matrix and are then called chondroblasts. They move apart as they deposit matrix, and when they are completely surrounded by matrix they are called chondrocytes. The mesenchymal tissue surrounding the blastema gives rise to the perichondrium.
Elastic cartilage : characterized by
great pliability
contain significant amounts of the protein elastin
Cartilage cells can give rise to benign chondroma
Or malignant chondrosarcoma tumors .
Growth
interstitial growth by chondrocytes
appositional growth by chondroblasts
regeneration :\
except in young children , damaged cartilage regenerate with difficulty and often incompletely why ?
because of the activity of the perichondrium in fracture , chondroblasts from the perichondrium invade the fractured area and regenerate new cartilage
in extensively damage areas , the perichondrium generate a scare of dense C.T. instead of cartilage
White fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its flexibility and toughness to the former of these constituents, and its HYPERLINK "http://en.wikipedia.org/wiki/Elasticity" elasticity to the latter. It is the only type of cartilage that contains type I HYPERLINK "http://en.wikipedia.org/wiki/Collagen" collagen in addition to the normal type II.
Fibrocartilage is found in the HYPERLINK "http://en.wikipedia.org/wiki/Pubic_symphysis" pubic symphysis, the HYPERLINK "http://en.wikipedia.org/wiki/Annulus_fibrosus" annulus fibrosus of HYPERLINK "http://en.wikipedia.org/wiki/Intervertebral_disc" \o "Intervertebral disc" intervertebral discs, HYPERLINK "http://en.wikipedia.org/wiki/Meniscus_(anatomy)" \o "Meniscus (anatomy)" meniscus, .
Intervetebral disks : the disks have two components
fibrous annulus fibrosus
nucleus pulposus the intervertebral disc acts as a lumbricated coushion that prevent adjacent vertebrae from being eroded
by abrasive forces during movement annulus fibrosus: has an external layer of dense C.T. the nucleus pulposus is situated in the center of the annulus fibrosus .
repulsion of the annulus fibrosus , results in explosion of the nucleus pulposus and concomitant flatting of the disk. Frequently slips from its position between the vertebrae , it moves towards the spinal cord compress the nerves and result in sever pain and neurological disturbance chondrocyte function depends on a proper hormonal balance , the synthesis of sulfated GAG is accelerated by growth hormones , thyroxin and testosterone slowed by cortisone and hydrocortisone.