LEC45: Cartilage & Bone Flashcards
2 structures in cartilage
chondrocytes: cartilage cells, extracellular matrix
components of cartilage extracellular matrix
1) collagen fibers
2) ground substance
3) water
components of ground substance of ECM?
proteoglycans: hyaluronic acid + core proteins + chondromucoproteins (mucopolysaccharides and GSGs)
function of components of ground substance of ECM?
thicken the matrix, proteoglycans especially hold together matrix
water’s effect on matrix shape?
negative charge organizes water into stiff colloidal gel; makes matrix function like shock absorber; more water = bigger matrix
what happens to astronatus’ cartilage discs when in weightless environment?
discs enlarge
what happens to our height overnight, why?
we grow taller because water has chance to get back into disc overnight, saps during the day
what is lacunae?
artifactual appearance of chambers that chondrocyte cells occupy in cartilage; appear when cells are fixed, cells shrink away from matrix walls
3 types of cartilage
fibrous, elastic, hyaline
fibrous cartilage collagen type
Type I
fibrous cartilage visible in matrix?
yes
fibrous cartilage have perichondrium?
no
is fibrous cartilage vascular?
yes
elastic cartilage collagen type?
type II
elastic cartilage in matrix?
yes, elastin fibers are in the matrix
elastic cartilage have perichondrium?
yes
is elastic cartilage vascular?
no
hyaline cartilage collagen type?
type II
how does hyaline cartilage matrix appear?
homogenous, because no fibrous or elastin type fibers, so looks homogenous under microscope - light goes right through
does hyaline cartilage have perichomdrium?
yes
is hyaline cartilage vascular?
no
how are nutrients distributed in elastic and hyaline cartilage?
because avascular, nutrients must diffuse or be pumped through the matrix; so avascular cartilage size is limited
what inhibits nutrient flow through avascular cartilage?
calcium, causes chondrocytes to die, hence calcium replaced by bone
when does cartilage die, and what happens as result?
when calcium put down into avascular cartilage, cartilage dies; bone takes over, becomes matrix
where is fibrous cartilage found?
pubic symphysis, intervertebral disc, joint menisci, tendon and ligament insertions into bone, anulus fibrosis of IV discs
where’s elastic cartilage found?
ear, epiglottis
where’s hyaline cartilage found?
respiratory tract, ventral ends of ribs, long bone epiphyseal plates, synovial joints
types of cartilage cells
1) perichondrial cells
2) chondroblasts
3) chondrocytes
what are perichondrial cells from / what do they become?
are flat mesenchymal precursor cells, in perichondrium; differentiate into round chondroblasts
“peri”
periphery
“blast”
baby cell
chondroblast function
divide, grow, synthesize the matrix
“cyte”
mature cell
chondrocyte function
are trapped within, and maintain, the matrix
what are isogenous groups of chondrocytes
groups of chondrocytes dividing, making daughter cells for interstitial matrix around them
what happens spatially when isogenous groups of chondrocytes are at work?
cells working separate from each other
in which area of cartilage do isogenous groups of chondrocytes work?
interstitial
how do isogenous groups divide?
mitotic divisions of pre-existing chondroblasts
which way does matrix expand, why?
from within, b/c it’s a pliable colloid gel
what is appositional growth?
perichondrial cells > chondroblasts (make matrix) > chondrocytes
where does appositional growth occur?
outer edges of cartilage
what occupies epiphyseal growth plates, what kind of growth occurs there?
cartilage
interstitial growth
where does long bone growth occur (region of bone)?
epiphysis
top of long bone
where does ossification of long bone occur?
metaphysis
where is growth plate re: regions of long bone?
between metaphysis, epiphysis
where in long bone does appositional growth occur?
epiphysis’s perichondrium - cells added to the outside, make matrix, grow outside of long bone
steps of bone growth
1) cartilage model
2) periosteal collar forms on diaphysis
3) calcification in diaphyseal cartilage
4) blood vessels invade and form marrow cavity, eroding away middle part
5) endochondral bone formation occurs on metaphyseal cartilage and becomes ossofied b/c calcium deposited there
6) blood vessels invade, erode epiphyseal cartilage
7, 8) 2o ossification centers form in epiphyseal cartilages
8,9) epiphyseal plate forms btwn meaphysis and epiphysis
9,10) metaphysis and epiphysis fuse, epiphyseal plate disappears
10) ossification complete
type of cells in zone of reseve cartilage?
quiescent cells
tpye of cells in zone of proliferating cartilage?
making matrix so isogenous groups
type of cells in zone of cartilage hypertrophy
cells that’ve made matrix already; become isolated cells
what occurs in zone of capillary invasion
marrow cavity forms
what occurs in zone of mixed spicules
dying cartilage and newly formed immature bone present
what is in zone of remodeled spicules
mature bone that’s taking on shape that it’ll have in adult
7 endochondral bone formation zones
1) reserve cartilage
2) proflierating cartilage
3) cartilage hypertrophy
4) cartilage calcification
5) capillary invasion
6) mixed spicules w/ dying cartilage and newly formed immature bone
7) remodeled spicules, mature bone
how is bone able to be stained/on slide?
decalcify bone so can cut it
what happens to bone as grow older?
it’s resorbed where not needed, added to where it is needed, therefore changing bone shape over time
what causes bone WIDTH increase?
intramembranous and appositional growth
what causes bone LENGTH increase?
endochondral and interstitial growth
bone originally forms from what?
mesenchymal tissue
in membrane model of bone growth, what occurs?
appositional growth, intramembranous ossification at periosteum
what does membrane model of growth lead to?
long bone width, remodeling shape, skull vault
in hyaline cartilage model of bone growth, what occurs?
interstitial growth, endochondral ossification at growth plate
what does hyaline cartilage model of growth lead to?
long bone length, skull base
intramembranous appositional ossification growth involves what?
only bone, eg skull vault
endochondral intersitial ossification involves what?
both bone and cartilage, eg metaphysis of long bone
what is major different between cartialge matrix and bone matrix?
bone matrix has crystals and therefore high mineral content, cartilage matrix does NOT have crystals and therefore has low mineral content
what is bone matrix comprised of?
osteoid + minerals
what is osteoid?
uncalcified “pre-bone” made of water, type I collagen, ground substance, + calcium + phosphate ions
minerals of bone matrix?
hydroxyapatite crystals Ca10(PO4)6(OH)2
what is unique about the length/weight of long bones?
very strong, but not very heavy because TUBULAR structure adds STRENGTH where forces are incurred (solid outer surface) but doesn’t add weight (hollow center)
what does cancellous mean
spongy, trabecular; meshwork of bony spicules
what are concentric layers of bone?
periosteum > compact/cortial bone > cancellous/spony/trabecular boney meshwork
cancellous bone matrix made of?
trabeculae / spicules
how do trabeculae arrange? Why significant?
trabeculae form right-angles to each other; prevents bone from twisting, bending breaking; distributes force over larger area to cortex
where does bone marrow go
in spaces between trabeculae (also fat there)
what occurs in osteoperosis?
trabeculae still at right angles, but become THIN - lose calcium, so framework brittle, fragile
where is compact/cortical bone?
in perimeter of bones
function of compact/cortical bone?
nearly solid; accouts for most of bone weight
forms of compact bone
circumferential lamellae and haversian system osteons
how many layers of lamellae in bone?
2 circumferential lamellae - outer and inner; also interstitial lamellae
fiber type of circumferential lamellae, and their arrangement?
type I collagen; in parallel layers; fibers oriented at 45 degrees relative to adjacent layers
fiber type and arrangement of haversian osteons?
type I collagen fibers in concentric layers, fibers oriented 45 degrees relative to adjacent rings
organization of cortex of bone, from outer to inner?
1) outer periosteal circumferential lamellae
2) haversian system osteons
3) inner endosteal circumferential lamella > marrow inside
what type of layers do osteons have?
concentric lamellae (like Onion)
what type of layers do periosteal circumferential lamellae have?
parallel (like Parfait)
what are concentric lamellae arranged around? What does it contain?
haversian canal, which has blood vessels, nerves
what connects adjacent Haversian canals? Function?
Volkmann’s canals; allow blood vessels to get in from periphery, and in from 1 column to another; run 90o to Haversian canals; no concentric circles of lamellae
cartilage cell precursors?
perichondrial
bone cell precursors?
osteoprogenitor
what makes cartilage matrix?
chondroblast
what makes bone matrix?
osteoblast
what is trapped in cartilage matrix?
chondrocyte
what is trapped in bone matrix?
osteocyte
what resorbs cartilage matrix
NOTHING!
what resorbs bone matrix?
osteoclasts
osteoblasts
activated osteoprogenitor cells aka make bone
osteoprogenitor cell
bone lining cell that covers quiescent bone surfaces
osteocytes
former osteoblasts, trapped within bone matrix
what do osteoclasts arise from
mononuclear phagocytic system; eat old bone that needs to die, be resorbed and reformed
what system are osteoclasts part of?
mononuclear phagocytic system
bone cells’ evolution
osteoprogenitor > osteoblast > osteocyte > osteoclast
what are osteoprogenitors derived from, where are they found, what do they give rise to?
from mesenchyme-type cells; found at periosteum; give rise to osteoblasts and osteocytes
where are osteoblasts, what do they do
on perimeter of matrix, lay down organic components of bone matrix
osteoid?
unmineralized bone
osteocytes’ characteristics
lost their major protein syntehtic apparatus; connected to adjacent cells by long cell processes allowing cell-cell communication, ion/fluid transfer
what are the are bone matrix “maintenance” cells
osteocytes
what are canaliculi?
small channels, contain cytoplasmic processes, from osteocytes; communicate w/ other osteocytes via GAP JUNCTIONS
what do canaliculi do?
allow cell processes to transfer nutrients, fluid, ions, signals, wastes; connect remote osteocytes to blood vessels in central Haversian canal; help resorb surrounding bone if osteocytes die
what is delimiting edge?
“cement line” or boundary between osteons of adjacent HAVERSIAN SYSTEMS, formed when new bone is made, and which canaliculi don’t cross
what is in high concentration in delimiting edge?
muccopolysaccharides
how do osteoclasts appear, why?
foamy, ruffled border because dissolved bone minera , highly folded surface for increased SA
is cartilage present in intramembranous bone formation?
no
what is intramembranous bone remodeling
building w/ osteoblasts on 1 side and resorption by osteoclasts on other side of bone area
what happens in osteoporosis re: osteoblasts, osteoclasts?
decrease in osteoblastic activity, but osteoclast numbers and activity unaffected
what happens to astronauts re: bones in space?
suffer bone loss due to microgravity
osteon “life cycle”?
1) osteoclasts make large hole in old bone; left over partial lamellae called “interstital lamellae”
2) osteoprogenitor cells migrate inf rom blood, differentiate into osteoblasts
3) osteoblasts deposit bone along perimeter of canal lumen in sequential layers, narrow lumen
4) osteocytes trapped in lacunae within lamina layers
relationship between bone canal size and osteon age?
large hole=younger; small hole=older
leftover pieces of bone called?
interstitial lamellae of old haversian system
whether cortical or cancellous, what are 2 bone classifications?
1) lamellar 2) woven
what is woven bone?
immature bone (fetal-3 yrs old); less mineral, more cellular; irregular fiber arrangement; first bone formed during fracture repair
immature bone (fetal-3 yrs old); less mineral, more cellular; irregular fiber arrangement; first bone formed during fracture repair
mature bone (3 yrs-adult); more mineral, less cellular; have layered fiber arrangement
how does lamellar bone appear under polarized light, why?
alternating light/dark pattern because collagen fibers in successive layers arrayed at 45 degrees to each other
what does lamellar bone have?
layers: Osteons=concentric, circumferential=parallel; spongy=parallel
what is first bone formed at growth sites?
woven bone, primary spongiosa
how are lacunae in woven bone?
randomly placed
nickname for woven bone, why?
“band-aid bone” b/c made quickly, slapped down at fracture repair sites
where can you find woven bone and lamellar bone re: compact/cortical or cancellous/spongy layers?
can find both woven and lamellar bone in both compact and cancellous layers - depends on when made, and for what
what do intramembranous and endochondral ossification have in common?
both involve making woven bone first and then remodeling it into lamellar bone
woven bone is made form which model of bone development?
either membrane or cartilage model; either way, ends up becoming lamellar bone
where does woven bone persist?
gamphosis (tooth-jaw), where tendon attaches to muscle
why might growth plate fracture result in stunted growth?
because woven bone slapped onto fracture site, causing premature ossification of cartilage, therefore stunting growth of long bone
phases of bone fracture repair?
1) reactive
2) reparative
3) remodeling
what happens during reactive phase of bone repair?
1) hematoma
2) inflammation, granulation tissue, blood vessel growth
what happens during reparative phase of bone repair?
1) soft callus of fibrous tissue and hyaline cartialge bridges fracture site
2) hard callus forms of woven bone - endochondrial inside callus, intramembranous outside at periosteum
what happens during remodeling phase of bone repair?
1) remodeling callus: woven bone replaced by lamellar bone: trabecular lamellar bone forms first, excess bone removed, trabecular replaced by compact bone, bone returns close to normal shape
what is rickets? What happens, why?
osteoid (so called pre bone) doesn’t calcify under conditions of poor calcium and phosphate ion levels
normal bone matrix percent organic v mineral?
30 percent organic (water, Type I collagen, ground substance), 70 percent minerals (calcium and phosphate in hydroxyapatite crystals)
osteopenia?
failure of osteoid to calcify; thinning cortices, lucent metaphyseal bands results; on x-ray, bone looks very opaque rather than dense
what is fibrodysplasia ossificans progressive?
over-calcification; ossifies muscle and locks joints, imprisons victim in a “second skeleton”
what is osteogenesis imperfecta?
defect in formation of type I collagen that forms bone matrix, result is baby’s extremeties positioned oddly because has multiple fractures; can be lethal
what influences bone formation and resorption?
parathyroid hormone (PTH)-regulates bone turnover, and Vitamin D- regulates mineralization of bone matrix
factors involved in bone remodeling
estrogens, calcitonin, glucocorticoids, progesterone, androgens, impact of mechanical constraints, genetic background, growth hormone, gonadotrophic (sex) hormones
who was adam ranier? Why does it matter?
only person to be classified as both a dwarf and giant; 3 ft 10 inches at age 21, then pituitary tumor caused overgrowth, measured 7 ft 8 inches at his death at age 51
