Bone Flashcards
1
Q
Describe and label the structure of bone
A
Exterior of compact bone, interior of spongy trabecullar/cancellous bone
2
Q
What are the main 2 types of bone?
A
Lamellar and woven bone
3
Q
Describe the two types of lamellar bone
A
Compact/cortical bone
- has central blood vessel associated with CT
- osteocytes lie within lacunae and are linked by caniculi arranged in bony layers
- have osteone/Haversian system
Spongy/cancellous/trabecullar bone
- occurs within bones of all shapes
- spicules are aggregated into bony trabecullae with blood vessels in between
- spaces between trabecullae consist of CT (endosteum)
4
Q
Describe woven bone
A
- temporary form of bone associated with development, fracture repair and bone tumours
- randomly arranged collagen fibres
- in most cases is replaced by lamellar bone
5
Q
What are the functions of bone?
A
- rigid and hard support
- protects vital organs
- contains bone marrow
- reservoir for Ca, PO4 and other ions
- transforms forces of skeletal muscle contraction into bodily movements
6
Q
What are the 3 main cell types and what are their functions?
A
- Osteoblasts - external and internal surfaces, synthesise osteoid (ECM), develop into osteocytes
- Osteocytes - located in lacuna between lamellae of calcified osteiod, communicate via canaliculi, maintain bony matrix
- Osteoclasts - external and internal surfaces; large, motile, multinucleated cells; on contact with bone develop a ruffled border sink in and digest bone to form lacuni
7
Q
What are the components of the bony ECM?
A
- osteoid - organic - collagen type 1 fibres, GAGs, Ca binding glycoproteins
8
Q
Describe the structure of compact bone
A
- Periosteum & endosteum - vascular CT on inner and outer surfaces; osteoblasts; forms outer and inner circumferential lamellae
- Volkmann’s canals & Haversian - branching network which penetrates diaphysis of long bone; lined with CT which is continuous with endosteum & periosteum; blood vessels & osteo-progenitor cells penetrate the bony shaft & form Haversian systems
- Osteones/Haversian system - central canals lined with osteoprogenitor cells; osteoblasts form concentric lamellae; collagen fibres have a specific orientation which gives strength; constantly being remodelled
9
Q
How do Haversian systems form?
A
- Forms under the periosteum - longitudinal ridges form along the diaphysis & periosteal cells differentiate into osteoblasts; periosteal capillary is found in the groove; new bone extends adjacent ridges towards each other
- Ridges fuse, groove becomes bony tunnel enclosing the blood vessel
- Additional bone lamellae are deposited around the tunnel, then converted into Haversian canal containing blood vessel
- Haversian vessel continues to recieve blood through Volkmann’s canal which extend obliquely across the diaphysis
- When bone reaches full size, outer and inner circumferential lamellae provide boundaries of the compact bone consisting of Haversian systems
10
Q
What are the 2 ways in which the bony skeleton develops?
A
- Intra-membranous ossification
- Endochondral ossification
11
Q
Describe intra-membranous ossification
A
- forms directly from osteogenic CT
- there is no pre-existing hyaline cartilage model
- flat bones of the skull, mandible and maxilla are formed by it
- occurs in areas of appositional growth and repair
12
Q
Describe endochondral ossification
A
- replaces hyaline cartilagenous model in embryo with bone
- responsible for growth of long bones in embryo and juvenile
*woven bone is produced first but is replaced by lamellar bone*
13
Q
Describe the first stage of endochondral ossification
A
- hyaline cartilage acts as a template
- osteoprogenitor cells of perichondrium form the periosteal collar
- chondrocytes proliferate then undergo hypertrophy which initiates the formation of the primary ossification centre
- hypertrophic chondrocytes secrete VECGF to induce sprouting of blood vessels from perichondrium
- blood vessels form the periosteal bud brach in opposite directions
- calcification and apoptosis of hypertrophic chondrocytes occurs
14
Q
Describe the second stage of endochondral ossification
A
- secondary centres of ossification and the epiphyseal growth plate forms
- blood vessels and mesenchyme infiltrate the epiphysis and establish a secondary centre of ossification
15
Q
Describe the 3rd stage of endochondral ossification
A
- termination of growth and closure of epiphyseal growth plate
- blood vessels from the diaphysis and epiphysis intercommunicate
- all epiphyseal cartilage is is replaced by bone, except for articular surface
- epiphyseal plate is replaced by an epiphyseal line - gradually occurs from puberty to maturity until long bone can no longer grow in length
