lecture 5: bone Flashcards
bone is hypocellular meaning
has few cells
bone stains pink because
it is eosinophilic
most ECM is made from collagen, which is positive
compare cartilage and bone
- *Cartilage**
- large, rounded cells found in clusters
- texture: firm but gel-like, elastic
- avascular
- low metabolic rate
- ECM Type II collagen and Aggrecan (sulfated PG) (negative purple)
- permeable
- continued growth
- *Bone**
- ellipsoid, isolated cells encased in mineral, hypocellular
- mineralized, hard
- vascularized
- high metabolic rate
- ECM: type I collagen, small PGs, glycoproteins
- impermeable
- complex structure with capacity for remodeling
ECM of cartilage vs bone
cartilage: type II collagen and aggrecan (sulfated PG) (make negative- purple stain)
bone: type I collagen, small PGs, glycoproteins (areas to bind calcium, positive- pink stain)
compare texture of cartilage and bone:
cartilage: firm, gel like, high tensile strength, elastic
bone: mineralized hard
compare cells in cartilage and bone
cartilage: large, rounded cells, often in clusters, encased in ECM
bone: ellipsoid, isolated cells encased in mineral, more hypocellular
compare metabolic rate and growth in cartilage and bone
cartilage: low metabolic rate, avascular, capacity for continued growth
bone: high metabolic rate, highly vascularized, complex structure with capacity for remodeling
% make up of ECM of bone
inorganic : 75% of bone
mineral hydroxyapatite
organic: 25 %
type 1 collagen: 90%
small proteoglycans and glycoproteins: 10%
type 1 collagen fibril
type 1 collagen molecules form head to tail and have spaces in between that form “hole zone”, gives stripped appearance
hole zones are where calcium deposits
“quarter staggered”
hole zones in bone is where ___
calcium and phosphate deposits
this brings more calcium and phosphate which allows minerals to grow and fill space in between type 1 collagen molecules
collagen molecules do not mineralize, only space in between that is why bone is at most 50-75% mineralized
Why is bone at most 50-75% mineralized
collagen molecules do not mineralize, only space in between that is why bone is at most 50-75% mineralized
allows some bending of bones
two type of bone formation
endochondral ossification
intramembranous ossification
endochondral ossification is found in what type of bones
axial and appendicular skeleton, some facial bones
where does intramembranous ossification take place
most cranial bones, periosteal bones
endochondral ossification
simple explanation
mesenchyme undergo chondrogenesis form
cartilage
cartilage undergoes hypertrophy and degradation and is replaced by trabecular bone (on inside), and bone marrow cavity
intramembranous ossification
simple explanation
mesenchyme
compact bone (no marrow)
happens on outside of long bones and skull bones
steps of endochondral ossification
mixed process of endochondral and intramembranous ossification
- hylan cartilage blueprint
- perichondrium replaced with periosteum (compact bone- intramembranous ossification )
- cartilage cells undergo proliferation and hypertrophy, during hypertrophy cartilage cells produce different ECM (matrix that can mineralize)
- vessels invade bring cells to breakdown cartilage and make bone
- cartilage is broken down by chondroclasts leaving hypertrophic ECM backbone
- bone is deposited by osteoblasts onto this hypertrophic ECM backbone
- same process happens at ends of bones, growth plate in between
- continues until bone fully formed and two sites of ossification fuse
how does perichondrium change to periosteum
progenitor cells in the perichondrium differentiate into osteoblasts instead of chondroblasts
how is matrix produced by hypertrophic cartilage cells different
can mineralize
matrix can be invaded by blood vessels (periostial blood)
what kind of cells are brought into the bone during endochondral ossification
clasts, that eat cartilage cells (chondrocytes) and ECM matrix
osteoprogenitor cells- (differentiate into osteoblasts that make bone)
stem cells that form marrow environment
stem cells that form hematopoetic lineages
where does cartilage remain after bones are finished growing
what is different about this cartilage?
caps of bone- ends articular surface
no longer has perichrondrium - does not have cells to make cartilage- can not repair or regrow
protects bone
epiphysis
end of bones
diaphysis
shaft of bone
periosteum
two layer membrane that covers bone
outer layer: dense irregular connective tissue with blood vessels
inner layer: progenitor cells
inner membrane of bone
endosteum
endosteum
inner membrane of bone
branched- has progenitor cells for bone and marrow stroma
metaphysis
area of bone between epiphysis and diaphysis that contains growth plate and its products (endochondral ossification)- trabecular bone
bone formed by endochondral ossification is called
trabecular
spongy
cancellous bone
and marrow
bone formed by intramembranous ossification is called
periosteal
cortical
dense
compact
what is this
endochondral ossification derived bone:
trabecular bone (spongy bone)(pink with purple center which is remnants of hypertrophic cartilage)
marrow (white with purple red blood cells)
intramembranous ossification
bone used for structural support
mesenchymal cells (star cells) differentiate into osteoblasts that start to secrete ECM bone matrix (type 1 collagen, small PG and glycoproteins (osteoid)
as the osteoblasts secrete more ECM, ECM starts to mineralize (mineralizing osteoid) osteoblasts get stuck and become osteocytes
occurs in outward fashion, concentric rings
matrix of bone that is not yet mineralized
osteoid
cytoplasmic projections of osteocytes that reach out and touch other osteocytes
filopodia
tiny canals through which osteocyte connect to each other
canaliculi
filopodia reach out and touch/ communicate with each other
home of osteocyte
lacuna
filopodia have calcium sensors and are bathed in interstitial fluid which allows for
calcium sensor: monitor EMC and determine if it needs to be broken down or made
interstitial fluid: can detect movement and detect pressure/ force put onto bone
cell that breaks down bone
osteoclast
(not a connective tissue type- made from hematopoetic cells- similar to macrophage)
secrete hydrochloric acid which demineralizes hydroxyapatite
removed matrix- forms resorption pit -Howship’s lacunae
large amount of lysosomes
pit of resorption made by osteoclast
howship’s lacunae
primary bone is changed to ___
secondary bone
primary bone gets eaten and deposited in rings to form osteons
IO: primary bone is unorganized, when it is remodeled it forms ___
secondary bone which is very organized in ring structures called osteons
rings of bone
lamellae
central canal of osteon
haversian canal
what lives in haversian canals
dense irregular connective tissue
blood vessels
and nerves
`mature secondary bone: other name
lamellae bone
perpendicular canals in bone
connect what to what
volkmann’s canals
connect periosteal vessels, to haversian canale vessels and to bone marrow
in trabecular bone new bone is formed
on outside, follows contour of hypertrophic cartilage underneath
in compact bone, bone is remodeled
by osteoclasts eaten bones and osteoblasts reform bone in a concentric circle (osteon)
flattened, line most bone surfaces, may represent quiescent osteoblasts
bone lining cells
osteoblasts
make bone
osteocytes
mature bone cells
non-proliferative, encased in mineral, extensive filopodia, monitor calcium levels and communicate with bone forming( osteoblasts) and bone resorbing (osteoclasts) cells
osteoclasts
break down or resorb bone
large multinucleate, form monocytic lineage, on bone surfaces
formation of bone
osteogenesis
direct differentiation of mesenchymal cells to osteoblasts which secrete bone matrix
intramembranous ossification
during skeletogenesis
bones increase in width and change their shape
primary bone is substituted by secondary
during adult life: bone remodeling
means for bone to adapt to mechanical pressure
calcium storage and release mechanism
during pathology: bone remodeling
calcium homeostasis disorders
fracture repair
bone remodeling is the balance of ___ and ___ controlled by ___
osteoblasts (make bone)
osteoclasts (eat bone)
osteocytes
