Lectures 14 + 15 - Bone Flashcards
outline the functions of bone
Support • Protection • Metabolic • Storage • Movement • Haematopoeisis
what is the composition of bone ?
and its structure ?
The cells - 2% within bone are
osteoclasts
osteocytes
osteoblasts
made of type I collagen -23 %
contain Minerals - 65% - Clacium, Phosphate and Hydroxyapatite
10% water
Bone structure outline?
Cancellous/spongy bone in the center - with gaps for the bone marrow
compact / cortical bone - dense and thick on the outside
surrounded by a periosteoum (dense CT)
bones are highly vascular- large amount of blood vessels, to suplly inner bone marrow (red) , yellow gets low supply) with O2 to preform its functions
also to allow new blood cells from heamopoieis in the red bone marrow into the blood
we learn about bone through the simplest - long bone
what are the regions of the long bone ?
in order
Proximal epiphysis metaphysis diaphysis metaphysis distal epiphysis
What is endochondral ossification ?
the process of growth of length of our long bones and also heals when we suffer fractures
out line the process of endochondral ossification ?
Zone of reserve cartilage fully grown
Zone of proliferation
Zone of hypertrophy
Zone of calcification growing
Zone of resorption Brand new
Followed by bone remodelling
at the bottom we have the meatphysis plate - the Zone of Ossification / resorption - made of Primary Spongiosa - vascular invasion and resorption of calcified cartilage - bone formation
remodelling: internal removal of spicules, replacement of woven bone with lamellar bone
and secondary spongiosa - branches of the meatphyseal and nutrient arteries
then the zone of calcificaiton - cell death
then zone of hypertrophy - accumulation of lipid, glycogen, alkaline phosphate, matrix calcification
then zone of proliferation - matrix production and mitosis
reserve zone - matrix production
these are the zones and the structural changes that occur in chondroctyes
so the cells produce matrix, proliferate and grow upwards to growth plate, while the cells at the bottom, die calcify and from bone
growth occurs at epiphysial growth plates
outline the process of long bone development
increase in length is endochondrial ossification
increase in width is intramembranous ossification
- Fetal hyaline cartilage model develops
made only of perichondrium - Cartilage calcifies, and a periosteal bone collar forms around the diaphysis (center of bone)
there is degenerating hypertrophic cartilage in the middle
developing periosteum at the metaphysis zone
- Primary ossificaiton center forms in the diaphysis
blood vessel of periosteal blood and endophyseal capillaries innervate into the bone
- secondary ossification center forms in the epiphysis
cappiliries now form ephiphysial blood vessels
have a medullary cavity and are developing compact bone at the edged of the diaphysis - forming epiphysial growth plates
- Bone replaces cartilage, except articular cartilage on surface (joints) and epiphysisal plates (where bone growth occurs)
formed proper periosteum at edges made of compact bone
growth comes from ossification at ephiphysial growth plates - lengthening bone
- epiphyseal plates ossify and form epiphysial lines
articular cartilage on surface
a ephiphysial line surrounded by spongy bone
a medullary cavity
outline the process of intramembrous ossification
Development of flat bones Skull Clavicle Scapula Pelvis
the thickening of long bones at their periosteal surfaces
Differentiation of mesenchymal stem cells (MSCs): 1• => Osteoprogenitor cells 2• => Osteoblasts(deposit matrix) 3• => Osteocytes 4• Followed by bone remodelling
MSC’s diff into osteoblasts will lay down collagen fibers and send out projections into matrix
once fully differentatied - collagen fibers impregnated with hydroxyapatite crystals to form mineralized bone matrix
osteocytes in lacuna (from osteoblasts)
osteocyte process innervate the canniculi
what is bone remodelling ?
Two steps: 1. Osteoclasts make a wide tunnel in the bone (cutting cone) 2. Osteoblasts make a smaller tunnel of cortical bone (closing cone)
Once a bony spicule has formed, it is remodelled in the same way whether it was formed by endochondral or intramembranous ossification
OsteoBLASTS - Bone DEPOSITION
OsteoCLASTS - Bone RESORPTION
mature bone is continuously remodelled - impact exercise in many directions strengthen bone by promoting bone remodelling to strengthen it
what is trabecular bone ?
its structure ?
- Spicules grow and merge into trabeculae
- Bone marrow is present in spaces between trabeculae
structure - many spaces still with bone marrow
growth occuring from trabeculae
what is Woven bone ?
its structure ?
- An immature intermediate between trabecular and cortical bone
- Trabeculae merge together
- Physiological:
- Embryonic development of bone
- Fracture repair
- Pathological –Paget’s disease
structure
more dense
trabecula merge
what is Cortical bone ?
its structure ?
process goes - trabecular —> woven —-> cortical/compact bone
structure
looks like many circular rings - osteons
Central or haversian canals - are the main blood vessels longnitudinally with lateral volksmans cannals
this is surrounded by rings of bone deposition - lamellae
osteons connected by interstitial lamellae
where osteons meet are cementing lines
has an outer circumfrential lamellae surrounded by periosteum and endosteum
cancellous bone has now haversian or volksmans cannals as it is surrounded by blood supply
summarise bone formation
Endochondral ossification—->cartilage template —–> calcification of dead chondrocytes and matrix ——> bone remodelling—–>feed into 2.
Intramembrous ossification—–> mesenchymal stem cells ——> osteoprogentor cells——-> osteoblasts——> bone remodelling ——> feed into 2.
- Bony spicule —–>trabeculae —–> woven bone——> compact bone
how do we undergo bone fracture repair ?
- Hematoma formation
we from a hematoma - blood clot around the break/fracture
done by bleeding and haemostasis, cell necrosis and inflammation
macrophages will remove the blood clot eventually
- Fibrocartilaginous callus formation
the external callus forms - splints the bone
, new blood vessels invaginated
we get spongy bone trabeculae forming
internal callus has fibrous tissue and cartilage
done by angiogenisis
granulation tissue
fibroblasts produce collagen
hyaline cartilage formation
- Bony callus forms
made of spongy bone
trabecullar bone- undegoes IM and EC ossification
- Bone remodelling
compact bone reshaping
get a healed fracture
what is osteoporosis ?
Osteoporosis
• Loss of bone mass due to higher osteoclastic activity relative to osteoblastic activity
• Leads to larger spaces between trabeculae, giving a ‘porous’ appearance
• Risk factors:
• Age –Osteoblast function declines with age
• Post-menopause –Enhanced osteoclast activity
• Genetic
• Dietary calcium insufficiency
• Physical inactivity
• Cigarette smoking
