Chapter 4
Cartilage and Bone
1. Cartilage:
organ=Cartilage tissue+perichondrium
1)
structure of cartilage tissue
---cell: chondrocyte
---cartilage matrix
① chondrocyte:
---Structure: LM
embedded in cartilage
lacuna
peripheral cells:
--small and immature
--single and flattened
central cell:
--large and mature,
--round and in group of 2-8 cells
--small and round nucleus
--basophilic cytoplasm
--EM: rich in RER and Golgi complex
*isogenous group: several cells locates
in one lacuna, which are derived from a
single(same) parent cell
② Cartilage matrix
---ground substance:
proteoglycan:
--same to loose CT
--there are more chondroitin sulfate distributed
at the periphery of cartilage lacuna---called as
cartilage capsule(basophilic)
chondronectin
water
---fiber: type and number of fiber depends on the
type of cartilage
2) Classification: according to the fiber
a. Hyaline cartilage:
less collagenous fibril←type II collagen
articular surface, rib cartilage, trachea and
bronchi
b.
Fibrous cartilage:
large amount of collagenous fiber bundles
cells are small and less
intervertebral disc, symphysis pubis
c. Elastic cartilage:
large amount of elastic fiber
external ear, epiglottis
3) perichondrium
two layers:
---out layer: contain more fiber-protection
---inner layer: more cells-osteoprogenitor
cell(fusiform in shape)
4) growth of cartilage
---interstitial growth:
inner chondrocyte proliferation→ produce
fiber and matrix.
immature cartilage
---appositional growth:
osteoprogenitor
cell→cartilage
cell
(chondrocyte) → produce fiber and matrix.
growing and mature cartilage
2.Bone
---consists of bone tissue, periosteum and
endosteum, bone marrow
1)
Bone tissue
① Cells:
a. osteoprogenitor cell: stem cell
---structure:
fusiform, small
ovoid nucleus
slight basophilic cytoplasm
exist in periosteum and endosteum
---function: differentiated into osteoblast
and chondrocyte
b. osteoblast:
---structure:
LM:
single layer of
cuboidal or low columnar cell
round nucleus
basophilic cytoplasm
located on the surface of bone tissue
EM:
fine processes
rich in RER, Golgi complex
---function:
ⅰ.synthesize bone collagen fiber and ground
substance-osteoid
ⅱ.release matrix vesicle:
0.1um in diameter
membrane-coated
ALPase(Alkaline phosphatase), ATPase
and pyrophosphatase and phosphoester
(phospholipid)
calcium, crystal of bone salt and calbindin
function: promote calcification
c.osteocyte
---structure:
flattened cell with multiple
long thin processes
located in bone lacuna
and bone canaliculus
basophilic cytoplasm
adjacent cells connect in bone
canaliculus by gap junctions
---function:
Maintain bone matrix
regulate the balance of calcium
phosphonium
and
d. osteoclast
---structure: LM:
multinuclear large cell, 30-100um
6-50 nuclei
acidophilic cytoplasm
located at peripheral part of bone
EM:
ruffled border-processes
light zone: --under the ruffled border
--microfilament
primary lysosome, pinosome and secondary
lysosome
RER, mito. and Golgi
---function: dissolve and absorb bone matrix
②Bone matrix
---organic matter:
bone collagen fiber -collagenous fiber
(type I collagen)
ground substance:
glycosaminoglycan
glycoproteins:
osteocalcin: involve in calcification of
bone and regulate absorption of bone
osteonectin: related to adherence
between cell and bone matrix, regulate
calcification of bone
osteopontin
---inorganic matter: bone salts
Hydroxyapatite crystal:
Ca10(PO4)6(OH)2
pin-shaped
10-20 nm
longitudinal arranged
*bone lamella: bone matrix arranged in
layers at different direction
2) Architacture of long bone
Long bone is an organ, made up of
bone tissue(shaft and epiphyses),
periosteum and endosteum, bone
marrow
① shaft:
consists of compact bone
a. circumferential lamella:
/outer concentrically-arranged
/inner around inner surface of bone
b. Haversian system (osteon):
/cylindric structure, 3-5mm
/central canal: N, BV, CT
/Haversian lamella: 4-20 layers
c. interstitial lamella:
/irregular lamella
/remnant of Haversian
or circumferential lamella
*perforating canal:
/transverse canal
/connect with Haversian canal
② epiphyses: composed of spongy bone
---trabeculae:
formed by parallelly-arranged lamella
form a spongy-liked network
---Bone marrow: hemopoietic tissue
③ periosteum and endosteum: CT membrane
---periosteum: DCT
outer layer:more fiber bundles
form perforating fiber
inner layer:
rich in BV, N and osteoprogenitor cells
---endosteum: thin, a layer of osteoprogenitor cell
and CT
---function: provide nutrition and osteoblast for
bone growth and repairing
3)
osteogenesis
①basal processes
---formation:
osteoprogenitor cell→ osteoblast → osteoid
↓
↓calcification
osteocyte + bone matrix
bone tissue
---absorption: osteoclast →dissolve bone
tissue→reconstruction
②basal manner
a. intramembranous ossification:
---CT membrane →osteoprogenitor cell →
osteoblast→ossification
center→bone
trabeculae →thicker and longer
---flattened bone and irregular bone formed
in these manner
b. endochondral ossification: e.g. long
bone
ⅰ.formation of cartilage model
Mesenchymal cell→osteoprogenitor cell
→chondroblast→chondrocyte→cartilage
model( consists of hyaline cartilage and
perichondrium)
ⅱ.formation of bone collar
osteoprogenitor cell (perichondrium) →
osteoblast →bone tissue
* These bone tissue surround the central
segment of cartilage model as collar-shaped,
so called bone collar
ⅲ.formation of primary ossification
center and bone marrow cavity
chondrocytes of model center stop
differentiation, enlarge in size, calcification,
dead →CT, BV in periosteum enter
degenerating zone→osteoblast, osteoclast,
osteoprogenitor cell and mesenchymal cell
enter at same time→ossification→primary
ossification center
primary bone marrow cavity(space
between trabeculae) →bone marrow
cavity
ⅳ.Formation of secondary ossification
center and epiphyses
secondary ossification center appears
at the two end of long bone(epiphyses)
epiphyseal plate: cartilage layer
between epiphysis and bone shaft,
growing zone
③ Further growth of bone
---Become longer:
by growth of epiphyseal plate
from epiphyses to shaft, four zones can be seen:
i. reserve cartilage zone: cell is small, round and
basophilic
ii. proliferating cartilage zone: cell is flattened,
isogenous group cell arrange in single line
iii. calcified cartilage zone: cell become large,
mature, round and degenerated, strong
basophilic
iv. ossification zone:
---become thicker: periosteum cell →
osteoprogenitor cell→osteoblast