Cartilage and bone Flashcards
Perichondrium consists of
proteoglycans and type 1 and 3 collagen
Cartilage matrix consists of
type 2 collagen and proteoglycans
Hyaline cartilage is mainly composed of
Type 2 collagen and aggrecan
Most abundant collagen type
2
9,11,6 also prevalent
ECM consists of
collagen and proteoglycans
Articular cartilage has no
perichondrium , but a periosteum
MMP does what
breaks down aggregan and proteins
Fibrocartilage contains what type of collagen
Type 1
Bone matrix contains which type of collagen
Type 1
osteoblasts and osteocytes are of which lineage
Mesenchymal
Osteoclasts are of which lineage
Monocytic/macrophage
Matrix vesicles contain
enzymes that help nucleate the hydroxyapatite to form crystals
Molecules of osteoclasts that help break down bone
cathepsin-K and matrix metalloproteins
Describe regulation of osteoblasts and osteoclasts
- Osteoblasts secrete M-CSF, which binds to a receptor on monocytes causing them to turn into macrophages.
- Macrophages express RANK receptor on the surface
- Osteoblasts synthesize RANK-L which binds to RANK-R on the macrophages and causes the macrophages to turn into osteoclast precursors, then resting osteoclast and then functional osteoclasts.
- Osteoblasts also secrete osteoprotegerin (OPG) . OPG also binds to RANK -L with greater affinity than RANK-R. The binding of OPG to RANK-L prevents the osteoclasts precursors from becoming functional osteoclasts. Osteoprotegrin is a natural inhibitor of osteoclast formation and could be used to prevent osteoporosis.
Lateral mesoderm
appendicular skeleton
Intramembranous ossification
mesenchyme condenses and forms bone blastema which then differentiates into osteoblasts and lays down bone layers (appositional growth ) then the osteoblast become osteocytes
Endochondrial ossification
Starts out as undifferentiated mesenchymal cells .. these cell proliferate and diff into chondrocytes rather than osteoblasts. Then perichondrium then forms and becomes vascularized and it will secrete regulatory factors.
The chondrocytes hypertrophy. Then they die once they 1. mineralize the matrix, and 2. secrete factors that will cause vasculature to come into the bone.
Then the osteoprogenitor cells come in either from the perichondrium or from the vasculature and lay down bone matrix to remodel cartilage to bone. This starts in the center which is the primary ossification center. Growth plate eventually closes.
FGFR3 mutation
results in inactivation (AD) Achondroplasia . Chondrocytes don’t divide.
Activating mutation in PTH/PTHrP
Jansen type metaphyseal chondroplasia
-cartilage doesn’t turn to bone
Inactivating mutation ofPTH/PTHrP
Blomstrand lethal chondroplasia
-accelerating hypertrophic diff , as soon as cartilage is formed, it turns to bone.
Local growth factors
FGF and PTH/PTHrP
GH regulates
expression of insulin like GFs (insulin like GF can act locally or systemically).
If fracture is big enough, it will go through which repair mechanism
Mesenchymal cells will go directly into bone.
