Bone Flashcards
What is endochondral ossification?
The replacement of pre-existing hyaline cartilage with bone
Most bones of the body develop by __________ ossification
Particularly which sort of bones
Endochondral
Long bones
Hyaline cartilage is _______ to become bone
Mineralised
What is the middle portion of a bone called?
Diaphysis
What is the portion of bone between the middle of the bone and the epiphyseal growth plates called?
Metaphysis
What is the end of a bone called? (After the epiphyseal growth plates)
Epiphysis
When do the epiphyseal growth plate of long bones disappear? What are these epiphyseal growth plates replaced by?
After growth ends (in adults)
Compact bone
In an embryo, long bones begin as a hyaline cartilage template, how do they develop by endochondral ossification?
1) collar of compact bone appears in the shaft (6-8 weeks)
2) a primary ossification centre is formed at the diaphysis
3) central cartilage calcifies
4) artery penetrates the centre and supplies bone depositing osteogenic cells (8-12 weeks)
5) Medulla becomes cancellous bone
6) cartilage forms epiphyseal growth plates
7) secondary ossification centres form at epiphyses
8) epiphyses ossify
9) epiphyseal growth plates move further apart and bone lengthens
(Prepubertal)
10) growth plates replaced by compact bone (mature adult)
What are the 3 different type of bone cells?
Osteoclasts
Osteoblasts
Osteocytes
When does an osteoblasts become an osteocyte?
Once it is completely surrounded by bone
What is the function and a characteristic feature of osteoclasts?
Resorb and deposit bone/useful in bone remodelling
They are multinucleate
The synovial membrane contains macrophages to…
Remove debris from a joint
What is intramembranous ossification?
The formation of bone from condensations of mesenchymal tissue
Which sorts of bones develop by intramembranous ossification?
Flat bones e.g. Skull, pelvic bone, clavicle
As well as help in the development of flat bones, intramembranous ossification is important in…
The thickening of long bones
What are the stages of intramembranous ossification?
1) MSCs —> osteoprogenitor cells —-> osteoblasts
2) osteoblasts lay down an EM with a lot of type 1 collagen (osteoid)
3) osteoid mineralises —>bony spicules
4) osteoblasts —> osteocytes
5) bony spicules —-> trabecullae —-> woven bone
5) replaced by the lamellae of mature compact bone
What do osteoclasts release to help in the remodelling of bone?
H+ ions and lysosomal enzymes
Where is compact bone found?
Forms the external surfaces of bone
What is the structure of cancellous bone?
Network of bony columns
What is found between the spaces in cancellous bone?
Bone marrow
What is the periosteum?
Connective tissue with blood supply and fibroblasts on the outside of compact bone
What is the endosteum?
The connective tissue between the compact bone and cancellous bone
What is the structure of compact bone?
Consists of lamellae of bone in circular structures called osteons
What is in the centre of an osteon?
Osteon canal containing blood vessels and nerves
What do Volkmann’s and Haversian canals contain? How do they appear in an osteon?
Blood vessels, lymphatics and nerves
Haversian canals run parallel to the osteon central canal
Volkmann’s canals run perpendicular
Where are osteocytes in compact bone?
Embedded between lamellae
How do osteocytes communicate with each other?
They have slender cytoplasmic processes which reach out to adjacent osteocytes
Connect via gap junctions
What is a difference in structure between cancellous and compact bone?
No volkmann’s/haversian canals in cancellous bone
What is the general % composition of bone?
65% calcium hydroxyapatite crystals
23% type 1 collagen
10% water
2% non collagen proteins
Why does bone breakage result in bleeding?
Blood vessels are broken
What are the four general steps in bone fracture repair?
1) haematoma formation
2) fibrocartilaginous callus formation
3) bony callus formation
4) bone remodelling
Which cells remove dead/damaged tissue when a haematoma forms during a fracture? Which cells remove the blood clot?
Phagocytic cells/osteoclasts
Macrophages
What happens in the fibrocartilaginous callus formation stage of bone fracture repair?
New blood vessels enter the fracture site
Procallus of granulation tissue
Fibroblasts —-> chondrocytes and collagen fibres
Hyaline cartilage sleeve formed
Osteoblasts invade fracture site and form spongy bone
What happens in the bony callus formation of bone fracture repair?
New bone trabecullae appear
Fibrocartilaginous callus —-> bony callus (cancellous bone)
Which forms of ossification are used in the repair of a bone fracture?
Both
What happens in the bone remodelling stage of bone fracture repair?
Callus of cancellous bone —> compact bone (at cortical regions)
Bone is remodelled to original shape by osteoclasts
What are the three types of bone grafting?
Autograft
Homograft
Heterograft
Which particular type of animal bone works reasonably well in bone grafting?
Calf bones after refrigeration
What is osteoporosis? What does it result in?
A metabolic bone disorder where mineralised bone is decreased in mass
Increased susceptibility to fractures
What are the most common fractures as a result of osteoporosis?
Fractures of the vertebral bodies and hip
Is there a higher risk of osteoporosis in males or females?
Females
What are the two types of primary osteoporosis?
Type 1
Type 2
Which group is most affected by type 1 osteoporosis? What is the cause?
Post menopausal women
Oestrogen withdrawal —> increased osteoclasts
Which group of people is most affected by type 2 osteoporosis? What is the cause?
Elderly
Compromised osteoblast function
What is the recommended calcium intake of postmenopausal women?
800mg/day
