18 Bone function and repair Flashcards
endochondral ossifaction
formation of long bones from cartilage template. Continued lengthening is by ossification at epiphyseal plates.
Intra-membranous ossification
the formation of bone from cluster of MSC (mesochymal stem cells) in the centre of bone eg flat bones. Not done by replacement of pre-existing hyaline cartilage template.
this process also contributes to the thickening of long bones at their periosteal surfaces by appositional growth.
Stages of intramembrane ossification
1 MSCs form a tight cluster
2 MSCs transform into osteoprogenitor cells and them transform into osteoblasts
3 osteoblasts lay down a osteoid
4 osteoid mineralises to form rudimentary bone tissue spicules
5 spicules join to form trabeculae, which merge to form woven bone
6 trabeculae replaced by the lamellae of mature compact bone
Skull bone
skull development is intramembranous. takes place after birth. skull needs to fit out during birth
mature bone
circular structure of the osteocytes in the osteon around the haversian canal: vein, artery nerve
haversian canal?
a series of tubes in the corticol bone
Volkmann’s canal
Volkmann’s canals are any of the small channels in the bone that transmit blood vessels from the periosteum into the bone and that communicate with the haversian canals.
Type of fractures?
transverse, linear, oblique nondisplaced, oblique displaced, spiral, greenstick, comminuted
Where does the bone strength come from?
in the cortical boone as lamellae are thought to be able to slip relative to each other to resist fractures.
osteons remodel themselves to thicken the bone.
exercise is key determinant of bone strength . inactivity increases bone resorption
What factors afect bone stability?
Activity of osteocytes: osteiod recycling, can scavenge osteoids into the lacunae.
Activity of osteoblasts: decomposition of bones. several stimulants of this.
activity of osteoclasts: bone resorption.
Nutrition: vitamin D3, vitamin C, vitamin K and B12
fracture repair overview
A haematoma is formed in which a granulation tissue arises.
the procallus of granulation tissue is replaced by fibrocartilaginous callus in which bony trabelculae are developing.
Endochondral and intramembranous ossificaiton give rise to bony callus of cancellous bone.
cancellous bone is replaced by compact cortical bone until remodelling is complete
Bone remodelling
osteoclasts make a wide tunnel in the bone (cutting cone) and then the osteoblasts make a smaller tunnel of cortical bone (closing cone)
Osteogenesis imperfecta
increased suscepibility to fracture
mutation in COL1A gene. so incorrect production of collagen 1 fibres. shortened height and stature
Rickets
vitamin d deficiency so poor calcium mobilisation and inefective mineralisation. weakened bone development, prone to fractures.
Osteomalacia
rickets of adult.
Vitamin D deficiency: increased osteoids and lower mineralisation. increased calcium reabsorption. caused by surgery (stomach/ intestines), kidney disease, sunlight protection, drugs.
