23 A - Cartilage and Bone Supplement Flashcards
(37 cards)
1
Q
3 types of cartilage
A
- hyaline
- elastic
- fibrous
2
Q
Proporties of hyaline cartilage
A
- most common
- large chondrocytes surrounded by cartilage matrix
- mainly type 2 collagen and chondroitin sulfate (GAG)
- articulating surfaces of joints, nose, larynx, trachea and bronchi
3
Q
Colour of hyaline cartilage
A
transparent
4
Q
Properties of elastic cartilage
A
- histology and matrix similar to hyaline (large chondrocytes surrounded by cartilage matrix)
- but matrix has elastic fibres/elastin
- chondrocytes arranged between fibres
- ear (pinna and ear canal) and epiglottis
5
Q
What colour is elastic cartilage>
A
yellow
6
Q
Properties of fibrous cartilage
A
- parallel rows of smaller chondrocytes embedded between type I collagen fibre bundles
- high tensile strength, resists pressure
- intevertebral disks, TMJ, pubic symphysis
7
Q
Where is hyaline cartilage found?
A
- articulating surfaces of joints, nose, larynx, trachea, bronchi
8
Q
Where are elastic cartilage found?
A
- ear (pinna and ear canal)
- epiglottis
9
Q
Where is fibrous cartilage found?
A
- intevertebral disks
- TMJ
- pubic symphysis
10
Q
3 mechanisms of bone formation
A
- endochondral ossification
- intramembranous ossification
- sutural ossification
11
Q
Explain endochondral ossification
A
- bones made from cartilage model
- condrocytes produce hyaline cartilage that is replaced by osteoid/bone from osteoblasts
- e.g long bones (epiphyseal growth plate), mandibular condyle (secondary cartilage) and base of skull (synchondrosis)
12
Q
Explain intramembranous ossification
A
- bones made directly from osteoblasts that have differentiated from mesenchymal stem cells
- like flat skull bones, facial bones, mandible, maxilla
13
Q
Explain sutural ossification
A
- similar to intramembranous - bone directly from osteoblasts from mesenchymal stem cells
- but with fibrous connection providing stability during growth
- e.g postnatal growth of skull bones
14
Q
List embryonic origins of skeleton
A
- trunk axial skeleton
- appendicular skeleton
- skull bones
15
Q
Explain the embryonic origins of the skeleton
A
- trunk axial skeleton from sclerotome of mesodermal somites - endochondral ossification
- appendicular skeleton from lateral plate mesoderm - endochondral ossification
- skull bones - roof and base from mesoderm or neural crest cells (roof - intramembranous ossi, base is endochondral)
- facial bones from neural crest cells - intramembranous ossification
16
Q
Development of endochondral bones
A
- early perichondrium is formed by chondroblasts derived from condensed mesenchymal cells
- cartilage model assumes shape of future bone and pericondrium becomes more prominent
- in diaphysis region, perichondrium becomes periosteum. Osteoblasts differentiate from osteoprogenitor cells in periosteum and produce collar of bone (cortical bone - intramembranous)
- cartilage matrix begins to calcify (dots)
- blood vessels invade cartilage model through bone collar and introduce osteoblasts and clasts. get formation of primary ossification centre
- bone trabeculae formed and link to bone collar
- secondary ossification centre established in epiphysis
17
Q
Growth in length of endochondral bones is … but thickness is …
A
- epiphyseal growth plate
- periosteum
18
Q
Cells involved with epiphyseal growth plate
A
- resting chondrocytes
- proliferating chondrocytes
- prehypertrophic chondrocytes
- hypertrophic chondrocytes
- then calcification zone
19
Q
What are resting chondrocytes?
A
resevoir of chondrocytes to replenish lost chondrocytes
20
Q
What are proliferating chondrocytes?
A
chondrocytes align in column and divide (secrete collagen matrix, collagen type II)
21
Q
What are prehypertrophic chondrocytes?
A
- chondrocytes begin to swell
- increased production of cartilage matrix (collagen type X)
22
Q
What are hypertrophic chondrocytes?
A
- fully matured chondrocytes
- eventually die by apoptosis
23
Q
What happens in the calcification zone?
A
- cartilage matrix being replaced by osteoblasts
24
Q
Explain mineralisation of endochondral bones
A
- matrix vesicles bud off from chondrocytes and induce mineral deposition between collagen II fibres
- first hydroxyapatite crystals catalyse formation of mineralisation foci - calcified cartilage
- osteoblasts surround calcified cartilage and deposit osteoid (bone matrix) that is later mineralised to bone
- mixed spicule contains calcified cartilage and bone - chondroclasts remove cartilage
25
Development of intramembranous bones
- mesenchymal cells in cellular periosteum differentiate to become osteoblasts which produce irregular bone type (woven bone)
- gradual turnover of woven bone to lamellar bone
- formation of primary osteons by osteoblasts surrounding blood capillary
- continued bone replacement produces highly organised, mature bone
- fewer cells, secondary and tertiary osteons, circumferential lamellae
26
What colour are osteoblasts?
yelloe
27
Development of sutural bones
- condensation of mesenchymal cells that form periosteum
- differentiation into osteoblasts that deposit woven bone
28
What is a suture?
- fibrous joints between skull bones
- enable skull bone growth in response to brain growth
29
How are sutures organised?
- cambrian layer - cellular for bone growth mediated by osteoblasts
- capsular layer - fibrous for stability mediated by fibroblasts
30
Histological sequence of sutures
- bone
- cells
- fibres
- cells
- bone
31
List molecular control methods of skeletal development
- induction of mesenchyme
- condensation of cells
- cell differentiation programme
- endochondral ossification
32
How is induction of mesenchyme a molecular control of skeletal development?
- notochord to sclerotome cells
- AER to lateral plate mesoderm cells
- neural fold to local environment to neural crest cells
- inducers - WNT, BMP, FGF, SHH
33
How is condensation of cells a molecular control of skeletal development?
- express N-cadherin (cell adhesion)
- TGF-beta signals stabilise condensation
- differentiation of osteo-chondroprogenitors
34
How is cell differentiation programme a molecular control of skeletal development?
- express Sox9 to chondroblasts to cartilage (matrix proteins of Collagen II, X) - perm or temp endochondral cartilage
OR
- express Runx2 to osteoblasts to bone (matrix proteins of Collagen I, Opn, Ocn) - intramembranous or endochondral bone
35
How is endochondral ossification a molecular control of skeletal development?
- ordered chondrocyte differentiation
- IHH, PTHrP, BMP regulatory loop
- RUNX2 also induces chondrocyte hypertrophy
OR
- VEGF secreted by hypertrophic chondrocytes induces vascular invasion - introduction of osteoblasts and clasts
36
Molecular control of endochondral bone formation
- PTHrP secreted by perichondrium and periarticular chondrocytes
- induces chondrocyte proliferation and inhibits IHH secretion
- IHH expressed by (pre)hypertrophic chondrocytes that are out of reach of PTHrP signals - IHH directly stimulates chondrocyte proliferation
- IHH stimulates PTHrP expression - negative feedback loop, coordinated chondrocyte differentiation
- IHH also stimulates osteoblasts of bone collar
37
Molecular control of intramembranous bone formation
- differentiation of mesenchymal stem cells into connective tissue
- osteoblast differentiation (Runx2 induces foramtion of preosteoblasts, osterix induces osteoblast differentiation - express RANKL on cell surface, secrete osteoprotegerin)
- osteoclast differentiation (M-CSF induces formation of preosteoclasts from hematopoietic stem cells - express RANK of cell surface - RANKL/RANK interaction induces fusion of preosteoclasts to form mature osteoclasts - OPG is a decoy receptor blocking this interaction)
- coordination of bone formation and resorption
