meneghini 2 Flashcards
what are the cells in the cartilage that synthesize the ECM?
chondrocytes
the ECM is made of?
GAGs and collagen fibers
it is the way to give nutrients and supply from the connective tissue to the avascular cartilage
3 types of cartilage
hyaline
fibrous
elastic
which type of cartilage induces the lubrification of synovial joints?
HYALINE CARTILAGE
Which type of collagen is the most abundant in hyaline cartilage?
type II collagen, it is the bulk of collagen fibers and help the cartilage to resist to intermittent pressures
proteoglycans structure
protein core+GAGs
what are the GAGs present in hyaline cartilage?
chondroitin sulfate and keratan sulfate
each GAG is composed of
long polymers of repeated disaccharide units made of
1 modified sugar (glucosamine or galactosamine)
1 uronic acid (glucoronate or iduronate)
what is the most abundant proteoglycan in hyaline cartilage?
-aggrecan
structure of aggrecan
100 chondroitin sulfate + 60 keratan sulfate+protein core
the negatively charged sulfate group of the GAGs have high affinity for water
hyaluronic acid
-GAG present in the hyaline cartilage
-bonded to aggrecan (proteoglycan aggregate)
-doesn’t form proteoglycans
-made of repeated disaccharide units of glucosamine and glucoronate
multiadhesive glycoproteins
-allow the interaction of the ECM with the cell surface
-mediate the interaction of collagen fibrils with proteoglycan aggregate
anchorin CII
multiadhesive glycoprotein
acts as a collagen receptor on chondrocytes to link collagen fibers to the cells
tenascin and fibronectin
allow the interaction between membrane receptors on chondrocytes and collagen fibers
-a sort of a bridge
characteristics of young chondrocytes
-basophilic nuclei
-pale cytoplasm due to large golgi
-large ER for protein synthsesis
-metabilically active in modeling the cartilage ECM
-present lipid droplets and glycogen storage
characteristics of old chondrocytes
-less metabolical active
-less basophilic nuclei and smaller golgi
what’s the name of the dense connective tissue that sorrund the hyaline cartilage?
perichondrium
can we have more than one chondrocyte in each lacuna?
yes
2 or 4 is frequent
–>its called isogenous group
are cells that have just divided
different regions of the matrix within hyaline cartilage
-capsular matrix
rich in proteoglycans
rich in collagen type VI
-territorial matrix
-less purple
-rich in collagen type II
interterritorial matrix
-less stained->less proteoglycan
aged cartilage
what can we find in the perichondrium?
-fibroblast that produce type I collagen
-chondrocytes progenitors that give rise to chondroblasts
-all the nutrients and the nervous signals that are needed for the correct function and for the survival of chondrocytes are in the perichondrium
cartilage can grow in 2 ways
-appositional growth
chondrocytes progenitors in the perichondrium become chondroblasts that syntehtise collagen II molecules. when completely embedded in collagen matrix they become chodnrocytes
-interstitial growth
within the already existing cartilage
chondrocytes proliferate and synthesize new ECM
what is absent in articular hyaline cartilage that is present usually in hyaline cartilage?
the perichondrium
->no chondrocyte progenitors
no new chondroblasts
no repair after damage of the tissue
3 zones of articular hyaline cartilage
superficial zone
in contact w synovial fluid
flattened chondrocytes
compact collagen type II fibers to sustain the pressure of the synovial fluid
intermediate zone
rounded chondrocytes
sparse
less organized fibers
similar to normal hyaline cartilage
deep zone
chondrocytes form sort of columns
elastic cartilage structure
similar as hyaline cartilage
-chondroblasts /chondocytes
-type II collagen
-aggrecan
-contains elastic fibers made of elastin
-can’t undergo calcification during aging
-present the perichondrium
fibrocartilage structure
-chondrocytes arranged in lines or isogenous groups inside lacunae->secrete type II collagen
-fibroblasts are present and produce type I collagen which makes this type of cartilage more resistant to compression
->shock absorber
-fibroblast generate versican (proteoglycan made of less chondroitin sulfate)
-no perichondrium
-can undergo calcification
the perichondrium is present in which types of cartilage
hyaline (no articular hyaline)
elastic cartilage
in which types of cartilages is the perichondrium absent?
articular hyaline cartilage and fibrocartilage
in which types of cartilages can calcification occur?
hyaline and fibrocartilage
in the diaphysis is more present compact or trabecular bone?
compact bone
what surrounds the external compact bone?
the periosteum
where is the marrow cavity present ?
in the diaphysis
is more present compact or trabecular bone in the epiphysis?
trabecular
metaphysis
between each epiphysis and the diaphysial shaft
types of collagen in bone
type I and type V
what is that makes the bone matrix more compact compared to cartilage?
the presence of hydroxyapatite crystals
OSTEONECTIN
multiadhesive glycoprotein
mediate attachment of hydroxyapatite crystal with collagen
OSTEOPONTIN
multiadhesive glycoprotein
mediate attachment of cells to the bone matrix
OSTEOCALCIN
protein that regulate blood calcium levels
can uptake calcium from the circulation
RUNX2
transcription factor that allows osteoprogenitor cells to differentiate into osteoblasts
osteoid
initial non mineralized matrix produced by osteoblasts
made of collagen type I and organic matrix protein
shape of inactive osteoblasts
flattened with elongated nuclei
shape of active osteoblasts
round and basophilic
passive bone mineralization 3 stages
- precipitation of salts
- nucleation
- crystallization
active bone mineralization
-happens in the osteoid
mediated by the matrix vescicles of osteoblasts that contain a lot of phosphate and calcium
(thanks to active transports and specific enzymes)
->first crystal, calcium ortophosphate is formed
the crystal goes out from the vesicle into the osteoid and into the matrix.
in the matrix we have a lot of calcium thanks to calcitonin and this calcium adds to the orthophosphate and there is the formation of hydroxyapatite crystal
->main component of mineralized matrix
thanks to what the osteocytes can go in direct contact with blood vessels?
canalicoli
osteocytes can be in 3 different states
quiescent
formative-metabolically active-release matrix molecules
resorptive->lysis of the matrix, release of calcium and phosphate in the blood for calcium and phosphate homeostasis
main cells that regulate the process of bone degradation
osteoclasts
derive from hematopoietic stem cells
large, multinucleated
reside in hownship lacunae
what’s the name of the canal that we have at the center of the osteon?
Haversian, contains blood vessels and nerves
what connects the different Haversian canals?
Volkmann’s canal
osteoporosis
mutation affecting osteoblasts
no bone apposition only resorption
weak bones
osteopetrosis
-mutation affecting osteoclast
-irregular bone growth, no bone resorption
