Bone formation and absorption Flashcards
Why are bones constantly remodelled?
Repairs breaks/injuries/microfractures
Change in response to stresses like exercise
Flow chart of the process of remodelling bone?
Quiescence - resorption - reversal - formation - mineralisation - quiescence
What happens during quiescence?
Nothing is occurring
What happens during the reversal stage of making bone?
Macrophages clear up debris left behind by osteoclastic activity
What happens during the formation stage of forming bone?
Osteoblasts lay down bone tissue
Where does bone growth occur?
At the epiphyseal plate
Which type of cell divides to bring about bone growth?
Chondrocytes
How do bones grow?
Chondrocytes (cartilage) replicate, die and are replaced by calcified cartilage and bone
What stages does cartilage go through at the epiphyseal plate?
Resting cartilage Proliferating cartilage Hypertrophic cartilage Cell death Calcified cartilage
What happens to epiphyseal cartilage in adults?
It is replaced by bone, leaving the epiphyseal line
How does bone thicken?
Osteoblasts lay down bone matrix
Results in groove forming alongside periosteal blood vessel
Forms tunnel containing new vessel
Remodelled and forms new osteon
New outer circumferential lamellae laid down
Factors affecting bone growth
Dietary intake - calcium/phosphate/vitamin D
Hormones - growth hormone/insulin/PTH/calcitonin
Where does bone thickening occur?
At the bone surface
What does the embryonic skeleton comprised of?
Mesenchyme in the general shape of a skeleton
What are the two patterns of bone formation?
Intramembranous ossification
Endochondral ossification
What is intramembranous ossification?
Forms flat bones of skull/mandible/clavicle within membrane
What is endochondral ossification?
Cartilage is replaced by bone
Describe the process of intramembranous ossification
Mesenchyme cells cluster together and turn into osteoprogenitor cells which turn into osteoblasts
This creates ossification centres (bone and bone matrix is laid down)
Osteoblasts form osteocytes, causing calcification
Trabeculae (spongy bone) begins to form
Periosteum develops on outside
What type of cells are osteoprogenitor cells?
Stem cells
Describe the process of endochondral ossification
Mesenchyme forms bone shape
Develops into chondroblasts which secrete cartilage ECM
This produces a hyaline cartilage model, which grows
Ossification centres (turn cartilage to bone) form
Secondary ossification centres develop
Articular cartilage and epiphyseal plate form
Describe the process of fracture repair
1) Hematoma stage - haemorrhage and clot formation occurs within a few days
2) Inflammatory stage - inflammatory cells appear, organisation and resorption of clot, soft callus forms
3) Hard callus - bony callus grows and bridges fracture site, trabecular bone laid down by osteocytes
4) Remodelling - bone is reorganised and original structures are restored
Flow chart of fracture repair
Hematoma - inflammatory stage - hard callus - remodelling
What factors regulate bone growth?
Diet, physical activity, hormones, genetics
What causes bones to be flexible?
Collagen
What causes bones to be rigid?
Mineral salts
Where does the growth of bone (length) occur?
Epiphyseal plate
Where does thickening of bone occur?
External surface
What do calcium and phosphate do to contribute to bone health?
Make bone ECM hard
What does magnesium do to contribute to bone health?
Helps form bone ECM
What does fluoride do to contribute to bone health?
Strengthen bone ECM
What does manganese do to contribute to bone health?
Activates enzymes to synthesise ECM
What does vitamin A do to contribute to bone health?
Stimulates osteoblasts
What does vitamin C do to contribute to bone health?
Synthesises collagen
What does vitamin D do to contribute to bone health?
Helps absorb calcium in gut
What do vitamins K and B12 do to contribute to bone health?
Synthesise bone protein
What is the active form of vitamin D?
1,25(OH)2D
What are the two routes that can create vitamin D?
Sunlight - skin - 7-dehydroxycholesterol
Food - vit D - liver - kidney
What is a deficiency of vitamin D called?
Rickets
Characteristics of rickets
Bone matrix fails to calcify
Weight-bearing bones bend
Deformed pelvis and rib cage
What is osteomalacia?
Adult rickets
Characteristics of osteomalacia?
Lack of vitamin D/calcium or renal disfunction
Poorly calcified bones
Soft bones = more frequent fractures
Bone pain
Why is exercise important for healthy bones?
Mechanical stress causes increases osteoblast activity, which means increased deposition of bone
No stress = more bone resorption than formation
When will bone homeostasis be achieved?
When osteoclasts (bone resorption) = osteoblasts (bone formation)
How are trabecular arranged to best support bones?
Arranged along stress lines which absorb compressive loads
They remodel in response to activity changes
What does growth hormone do?
Stimulates osteoblasts to form bone and increase bone mass
Stimulates chondrocytes to increase rate of cell differentiation
Function of chondrocytes
Secrete extracellular matrix
What are the two ways pituitary gigantism can occur?
Too much GH in childhood
Lack of oestrogen closes epiphyseal plates
What is osteogenesis imperfecta?
A genetic disorder that causes weak bones that break easily
What causes osteogenesis imperfecta?
Defects in collagen synthesis
What is osteogenesis deformans?
Defect in bone remodelling - osteoclasts absorb bone quicker, osteoblasts produce bone quicker
The new bone is longer and weaker
Which aspects of bone formation are of particular interest to forensics and anthropology?
Ossification centres, the time of appearance and the rate at which they grow
How is bone age measured?
Assessing expected growth using x-ray images
Which condition is caused by the over-secretion of GH in adulthood?
Acromegaly
Where is thyroid hormone produced?
The thyroid
What does thyroid hormone do?
Stimulates osteoblasts to promote bone growth
Where is insulin secreted?
Pancreas
What does insulin do to bones?
Increases synthesis of bone proteins to promote bone growth
Example of androgen
Testosterone
What do androgens do?
Responsible for bone strength in males
Why are gonadal steroids important for bones?
Important in regulating bone growth and development of peak bone mass
Why is oestrogen important for bone health?
Regulates bone formation and re-absorption
Shuts down growth at epiphyseal plate
What is osteoporosis?
Osteoclasts > osteoblasts
Bone mass and amount of collagen decreases
Haversian canals emerge and are filled with adipose tissue
Why does bone heal more rapidly than cartilage?
It has a better blood supply
