5.1 - Lecture - Cartilage + Bone Development Flashcards
Endochondral ossification
- one of two was bone is initially developed
- cartilage model is used as a precursor
- bones developed by this method are considered to be weight bearing bones ( bones of extremities + axial skeleton)
intramembranous Ossification
- 1 of 2 ways bone is initially developed
- bone is formed without cartilage precursor, in well vascularized area
- bones developed by this method: flat bones of face + skull, mandible, clavicle
Mesenchymal Cell
Part of the mesoderm and specific neural crest cells that differentiate, proliferate, migrate through the developing embryo
–> give rise to CT of adult + other tissues
Appositional Growth
- growth on an existing surface
- surrounding mesenchymal cells give rise to osteoprogenitor cells –> come into apposition with initially formed bone + differentiate into bone producing cells
Bone Collar
- layer of bone forming a cuff around the diaphysis of a cartilage model of developing bone (endochondral ossification)
- is located between the periosteum and the cartilage
= the first sign of ossification of long bones
Primary Ossification Center
- located in the diaphysis of long bones
- site where bone begins to form in the cartilage model ( endochondral ossification)
Secondary Ossification center
- Located in epiphysis of long bones
- formation of bone and breakdown of the cartilage model in the epiphysis is typically a post natal event
3 names for Woven Bone
= primary bone
= bundle bone
= nonlamellar bone
Woven bone is …
- Bone Tissue that is initially formed and considered immature
- has more cells + they are organized in a random pattern
= the major bone type in the developing fetus
Mature/Lamellar bone ..
- has less cells + arranged in an organized circular fashion typical of the lamellar structure of an osteon
Calcified cartilage matrix
- serves as the initial scaffolding for the deposition of new bone
- chondrocytes will undergo cell death in this area
- calcified cartilage will be removed by phagocytosis (as new bond is being laid down by osteoblasts)
Epiphyseal Cartilage/growth plate
- cartilage that remains between the epiphyseal and diaphyseal cavities following development of the secondary ossification center
- the epiphyseal growth plate allows for continued growth of long bone.
Zones of the epiphyseal cartilage/growth plate: what are they, what do they show
- they show the transitory appearance of the stages of remodeling of cartilage into bone Zones: A) hypertrophy B) Calcification C) resorption d) ossification
Articular Cartilage
= Hyaline cartilage found at the ends of a bone
- is found at all synovial/moviable joints of the body
- allows for smooth gliding of the articulating surfaces
Epiphyseal line
- represents the epiphyseal plate when the bones of the individual have completed growing
- no cartilage remains between the epiphysis and diaphysis
- site of epiphyseal plate is replace by bone tissue
What 3 embryonic sources give rise to the skeletal system
1) Paraxial Mesoderm
2) Lateral Plate Mesoderm
3) Neural Crest Cells
Paraxial mesoderm functions in skeletal system development by:
- Gives rise to somites with give rise to
a) scelerotome of somites forms axial skeleton - vertebral columns
- ribs
- base of skull
b) somitomeres - contribute to boen formation in the head region
Lateral Plate mesoderm functions in skeletal system development by:
forming bones of (apendicular skeleton):
- sternum
- limbs
- pelvic girdle
- soulder girdle
Neural Crest Cell functions in skeletal system development by:
- critical role in development of facial bones and flat bones of skull (+clavicle)
- they are the link between cranial/facial deformities which are mostly due to lack/failure of neural crest cell migration (e.g. Treacher Collins Syndrome, Cleft Palette)
What are the ways bone can be initially formed?
1) Intramembranous Ossification
2) Endocondral Ossification
What is Intramembranous Ossification?
= Direct mineralization of matrix secreted by osteoblasts (direct differentiation of mesenchymal cells into bone)
What is endochondral ossification?
formation of bone a pre-existing cartilage matrix
What is woven-bone
= first bone tissue formed
- also called primary bone
- will eventually be replaced by secondary bone (lamellar bone)
What are the 3 requirements for intramembranous ossification
A) enough tissue mass to produce appropriate amount of bone producing cells (enough neural crest cell invaded mesenchyme)
B) well vascularized tissue
C) adequate maternal nutrition
What is the developmental time frame for the start of intramembranous ossification
end of the 7th week of development
What is the role of Meckel’s Cartilage, and where is it found in the adult?
- Gives rise to none of the facial cartilage
- is basically a structural support for tissues to lay down around
- -> allows first cells of facial skeleton to lay down and differentiate
- eventually completely regresses (is not present in adult)
Steps of Intramembranous Ossification
A) Mesenchymal cells migrate + aggregate (froming a bone blastema) in areas where bone will form
B) Vascular network proliferation
C) mesenchymal cells differentiate into bone producing cells that become rounded and larger
D) Osteoblasts begin to lay down the bone matrix
E) Cells trapped in calcifying matrix differentiate into osteocytes
F) Woven bone is formed
G) remodeling of initial bone forms compact bone with lamellar arrangement around can cellos bone
What are the two layers of the periosteum?
1) inner circular layer - contains stem cells of bone
2) Outer fibrous layer - for protection
what is a bone blastema
Condensation of cells that will produce bone
what is an osteocyte
osteoblast that has trapped itself in the bone matrix it has made
Describe the H and E LM appearance of an osteoblast
- Cuboidal Shaped cell (because it is active)
- basophilic staining
- will often have clear osteoid layer at its apical membrane surface in developing bone regions
What is osteoid
= new, uncalcified bone material
- first element produced by an osteoblast
- appear as a pale stained area between the calcified matrix + cuboidal shaped osteoblast cells
What is bones are produced by endochondral ossification?
- bones that participate in weight-bearing
- e.g.
a) long bones of extremities
b) pelvic + shoulder girdles
c) vertebral column
Where would you find the oldest cells/cartilage in endochondral ossification
-cartilage in the center of the bone is the oldest, because it is the first laid down
What is the time frame for development of bone by endochondral ossification
6th week of development - hyaline cartilage bone models forms
8th week of development - primary centers of ossification are formed in bones
38 weeks - some secondary centers of ossification are present
after birth- most secondary centers of ossification are formed
Describe the differential staining of cartilage and bone in H and E stains under LM
Cartilage = basophilic Bone = eosinophilic
What is the first sign of ossification in endochondral ossification
the appearance of the bone collar around the cartilage model
What is the function of the Bone Collar
- prevents diffusion of oxygen resulting in degenerative changes in underlying cartilage:
A) chondrocytes hypertrophy, synthesize alkaline phosphate
B) surrounding cartilage matrix becomes calcified (calcified cartilage matrix)
C) blood vessels invade future bone - bringing in bone cells that begin forming the primary ossification center
What are the two regions cartilage remains when the secondary center of ossification is present, and which one is absent in fully grown adult tissues?
1) Articular Cartilage
2) Epiphyseal cartilage (absent in adult)
Describe articular cartilage
- covers articulating surfaces of joints
- no perichondrium
Describe epiphyseal cartilage
- responsible from growth of bones
- is the epiphyseal plate/growth plate that disappears in adult and leaves epiphyseal line as its marker
Briefly Describe Clinical Correlations between somites and bone developmental issues
- Groups of disorders are derived from the improper development of somites and the resulting affects on axial skeleton malformations
- characterized by vertabral segmentation dects, rib anomalies
e.g. - Spondylocostal dystosis syndrome (SCD)
(spondyl = vertebra, dystosis = disorder in development of bone, coastal = rib)
Briefly Describe Clinical Correlations between neural crest cells and bone developmental issues
- Cranial/facial regions of bone & the rearrangement + sculpting of facial prominences and pharyngeal arches are assembled largely through active migration of these cells
- genetic/molecular/cellular processes are temporally + spatially regulated to culminate in 3D structure of face
- they are also the starting constituent for majority of skeletal + CT tissues of face
- -> makes them susceptible to large number of defects
- Are sensitive during development to: Alcohol, Retinoic Acid, Gestational Diabetes among other factors
Briefly Describe Clinical Correlations between Lateral Plate mesoderm and bone developmental issues
- Linked thalidomide to its interference with vascular development
- this link to birth defects was a turning point in toxicology during pregnancy (such that drugs, and other factors can cross the placental membrane - is not a “barrier”)
Characteristic due to improper lateral plate mesoderm development are often:
A) Amelia = lack of limb development
B) Meromelia = partial limb development
(among others)
What are the five zones of epiphyseal cartilage development from least active to most active?
Zone 1: Zone of resting cartilage (reserve cartilage)
Zone 2: Zone of proliferating cartilage
Zone 3: Zone of hypertrophy
Zone 4: Zone of calcified cartilage
Zone 5: Zone of ossification and resorption
Describe the appearance of Zone of Resting Cartilage
- Zone 1
- typical hyaline cartilage with chondryocytes
Describe the appearance of Zone of Proliferating Cartilage
- Zone 2
- chondrocytes are dividing rapidly + forming columns of cells parallel to long axis of bone
- cells produce collagen fibers + cartilage matrix processes
Describe the appearance of Zone of Hypertrophy of Cartilage
- Zone 3
- Enlarged/swollen cells producing Type I and Type X cartilage
- facilitates vascular invasion and growth
- hypertrophy compresses cartilage matrix into thin septa between chondrocytes
Describe the appearance of Zone of Calcified Cartilage
- Zone 4
- loss of chondrocytes
- calcification of cartilage matrix
- calcified cartilage will serve as scaffolding for new bone
Describe the appearance of Zone of Ossification + Resorption
- Zone 5
- Bone tissue appears
- stem cells from periosteum invade cavities left by chondrocytes
- osteoblasts lay down primary bone on calcified cartilage matrix
- cartilage is resorbed (by osteoclasts?) leaving only primary bone
True or False: Bone growth plate changes in thickness
False: Bone is proliferating at same rate as cartilage is being resorbed
- plate does not change in thickness only in length
