L15- Bone formation and repair Flashcards
5 Types – What are they called?
long short flat irregular sesamoid
Long
Support Weight and Facilitate Movement
FEMUR
short
Cube shaped- stability and some movement.
The carpals in the wrist and the tarsals in the ankles
irrregular
protective role
- vertebre protect the spinal cord
- pelvis protects vital organs
flat
Protect Internal Organs
- ribs
- sternum
sesamoid
function to protect tendons from stress and wear.
These small, round bones are commonly found in the tendons of the hands, knees, and feet.
- patella
Which method: endochondral or intra-membranous ossification is used to make
them?
flat bones- intramembranous ossification
all other bones- endochondral ossification
Can you distinguish between these two methods of bone formation?
In endochondral ossification, a cartilage is formed as a precursor on which new bone is laid down.
Intramembranous ossification is the direct laying down of bone into the primitive connective tissue (mesenchyme) and there is no intermediate cartilage involved.
What are the differences between compact and cancellous bone?
Compact
- highly organised into osteons
- not porous
- much more dense
Cancellous
- randomly organised into trabeculae
- filled with bone marrow
- very light
When are bones made?
Ossification begins about the third month of fetal life in humans and is completed by late adolescence.
osteoblast
are the cells that form new bone.
ONE NUCLEUS
osteocytes
a bone cell, formed when an osteoblast becomes embedded in the material it has secreted.
osteoclasts
large multinucleate bone cell which absorbs bone tissue during growth and healing
What happens when a bone repairs itself? What are the different stages of bone repair called and can you describe what happens at each stage?
1) Haematoma formation
- A blood clot (haematoma) is formed in which granulation tissue arises
2) Fibrocartilaginous callus formation
- The procallus of granulation tissue is replaced by a fibrocartilaginous callus in which bony trabeculae are developing
3) Bony callus formation
- Endochondral and intramembranous ossification give rise to a bony callus of spongy/ cancellous bone
4) Bone remodelling
- Cancellous bone is replaced by compact cortical bone until remodelling is complete
1) Haematoma formation
Blood vessels in bone and periosteum break
A mass of clotted blood (haematoma) forms
Bone cells at the fracture edge die (no blood supply)
Swelling and inflammation occurs (granulocytes enter the site)
A procallus of granulation tissue (i.e. tissue rich in capillaries and fibroblasts) starts to develop
Phagocytic cells and osteoclasts begin to remove dead and damaged tissue
Macrophages eventually remove the blood clot
2) Fibrocartilaginous callus formation
New blood vessels infiltrate the fracture haematoma
Some fibroblasts produce collagen fibres
that span the break. Others differentiate into chondroblasts that give rise to a sleeve of hyaline cartilage
Simultaneously:
osteoblasts from the nearby periosteum and endosteum, (and multipotent cells from the bone marrow) invade the fracture site and begin bone reconstruction by forming spongy/ trabecular bone
3) Bony callus formation
Within a week, new bone trabeculae begin to appear in the fibrocartilaginous (soft) callus.
The trabeculae develop as the former fibrocartilaginous callus is converted to a hard (bony) callus of cancellous bone
Endochondral ossification replaces all cartilage with cancellous bone
Intramembranous ossification produces new cancellous bone in any gaps
Bony callus formation continues for about two months until a very firm union across the fracture site is formed
4) Bone remodelling
Cancellous bone begins to be re-modelled into compact bone, especially in the prior cortical region (i.e. in the region of the former bone shaft walls)
This process continues for several months (or even years)
The material bulging from the outside of the bone, and inwards, into the medullary cavity, is removed by osteoclasts
The final shape of the re-modelled area is the same as that of the original unbroken bone because it responds to the same set of mechanical stressors
How long does bone remodelling take for a child?
many months but usually <1 year
How long does bone remodelling take for an adolescent?
between 1 -5 years
How long does bone remodelling take for a young adult?
2-10 year
How long does bone remodelling take for an elderly person?
continuously
How long does bone remodelling take for a baby?
does not occur because nones not fully formed
How long does bone remodelling take for an infant?
usually <6 months (if walking)
bone remodelling rates is related to age how
inversely
all bones are formed through
ossification
ossification can take
1 of 2 forms, depending on the type of bone it is forming
flat bones (ribs, scapula, pelvis and skull) undergo
intramembranous ossficiation
intramembranous ossficiation
- mesenchymal cells within the fibrous connective tissue differentiate into osteoblasts
- These osteoblasts form ossification centres
- ostoeblasts begin to lay down osteoid (organic part of bone- collagen fibres)
- Some osteoblasts become trapped within the osteoid- then said to be osteocytes]
5) osteoid then calcifies and forms spicules, which aggregate into a honey form formation called trabeculae- as this thickens it forms spongy cancellous bone
6) periosteum forms
most bones in the body are formed via
endochondral ossification
endo
within
chondro
cartilage
ossification
bone formation
long bone development by endochondral ossification
embryo 5-6 weeks
- intitial cartilage model forms
embryo 6-8 weeks
- collar of periostesal bone appears in the shaft
fetus 8-12 weeks
- central cartilage calcifies
- nutrient artery penetrates (supplying osteogenic cells)
- primary ossificantion centre nformed in the middle of the diaphysis
Post natal
- medulla becomes cancellous bone
- cartilage forms epiphyseal growth plate
- epiphyses develop secondary centres of ossification
Prepubertal
- epiphyses ossify and growth plates continue to move apart lengthening the bone
mature adult
- epiphyseal growth plates replaced by bone
endochondral ossification involves
hyaline cartilage models
when does endochondral ossification begin
within the developing foetus (starts at 8 weeks
what is found at the articular edges of long bones
hyaline articular cartilage
- protects bone
