Bone formation and absorption

Question 1

Why are bones constantly remodelled?

Answer 1

Repairs breaks/injuries/microfractures

Change in response to stresses like exercise

Question 2

Flow chart of the process of remodelling bone?

Answer 2

Quiescence - resorption - reversal - formation - mineralisation - quiescence

Question 3

What happens during quiescence?

Answer 3

Nothing is occurring

Question 4

What happens during the reversal stage of making bone?

Answer 4

Macrophages clear up debris left behind by osteoclastic activity

Question 5

What happens during the formation stage of forming bone?

Answer 5

Osteoblasts lay down bone tissue

Question 6

Where does bone growth occur?

Answer 6

At the epiphyseal plate

Question 7

Which type of cell divides to bring about bone growth?

Answer 7

Chondrocytes

Question 8

How do bones grow?

Answer 8

Chondrocytes (cartilage) replicate, die and are replaced by calcified cartilage and bone

Question 9

What stages does cartilage go through at the epiphyseal plate?

Answer 9

Resting cartilage
Proliferating cartilage
Hypertrophic cartilage
Cell death
Calcified cartilage

Question 10

What happens to epiphyseal cartilage in adults?

Answer 10

It is replaced by bone, leaving the epiphyseal line

Question 11

How does bone thicken?

Answer 11

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

Question 12

Factors affecting bone growth

Answer 12

Dietary intake - calcium/phosphate/vitamin D

Hormones - growth hormone/insulin/PTH/calcitonin

Question 13

Where does bone thickening occur?

Answer 13

At the bone surface

Question 14

What does the embryonic skeleton comprised of?

Answer 14

Mesenchyme in the general shape of a skeleton

Question 15

What are the two patterns of bone formation?

Answer 15

Intramembranous ossification

Endochondral ossification

Question 16

What is intramembranous ossification?

Answer 16

Forms flat bones of skull/mandible/clavicle within membrane

Question 17

What is endochondral ossification?

Answer 17

Cartilage is replaced by bone

Question 18

Describe the process of intramembranous ossification

Answer 18

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

Question 19

What type of cells are osteoprogenitor cells?

Answer 19

Stem cells

Question 20

Describe the process of endochondral ossification

Answer 20

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

Question 21

Describe the process of fracture repair

Answer 21

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

Question 22

Flow chart of fracture repair

Answer 22

Hematoma - inflammatory stage - hard callus - remodelling

Question 23

What factors regulate bone growth?

Answer 23

Diet, physical activity, hormones, genetics

Question 24

What causes bones to be flexible?

Answer 24

Collagen

Question 25

What causes bones to be rigid?

Answer 25

Mineral salts

Question 26

Where does the growth of bone (length) occur?

Answer 26

Epiphyseal plate

Question 27

Where does thickening of bone occur?

Answer 27

External surface

Question 28

What do calcium and phosphate do to contribute to bone health?

Answer 28

Make bone ECM hard

Question 29

What does magnesium do to contribute to bone health?

Answer 29

Helps form bone ECM

Question 30

What does fluoride do to contribute to bone health?

Answer 30

Strengthen bone ECM

Question 31

What does manganese do to contribute to bone health?

Answer 31

Activates enzymes to synthesise ECM

Question 32

What does vitamin A do to contribute to bone health?

Answer 32

Stimulates osteoblasts

Question 33

What does vitamin C do to contribute to bone health?

Answer 33

Synthesises collagen

Question 34

What does vitamin D do to contribute to bone health?

Answer 34

Helps absorb calcium in gut

Question 35

What do vitamins K and B12 do to contribute to bone health?

Answer 35

Synthesise bone protein

Question 36

What is the active form of vitamin D?

Answer 36

1,25(OH)2D

Question 37

What are the two routes that can create vitamin D?

Answer 37

Sunlight - skin - 7-dehydroxycholesterol | Food - vit D - liver - kidney

Question 38

What is a deficiency of vitamin D called?

Answer 38

Rickets

Question 39

Characteristics of rickets

Answer 39

Bone matrix fails to calcify Weight-bearing bones bend Deformed pelvis and rib cage

Question 40

What is osteomalacia?

Answer 40

Adult rickets

Question 41

Characteristics of osteomalacia?

Answer 41

Lack of vitamin D/calcium or renal disfunction Poorly calcified bones Soft bones = more frequent fractures Bone pain

Question 42

Why is exercise important for healthy bones?

Answer 42

Mechanical stress causes increases osteoblast activity, which means increased deposition of bone No stress = more bone resorption than formation

Question 43

When will bone homeostasis be achieved?

Answer 43

When osteoclasts (bone resorption) = osteoblasts (bone formation)

Question 44

How are trabecular arranged to best support bones?

Answer 44

Arranged along stress lines which absorb compressive loads | They remodel in response to activity changes

Question 45

What does growth hormone do?

Answer 45

Stimulates osteoblasts to form bone and increase bone mass | Stimulates chondrocytes to increase rate of cell differentiation

Question 46

Function of chondrocytes

Answer 46

Secrete extracellular matrix

Question 47

What are the two ways pituitary gigantism can occur?

Answer 47

Too much GH in childhood | Lack of oestrogen closes epiphyseal plates

Question 48

What is osteogenesis imperfecta?

Answer 48

A genetic disorder that causes weak bones that break easily

Question 49

What causes osteogenesis imperfecta?

Answer 49

Defects in collagen synthesis

Question 50

What is osteogenesis deformans?

Answer 50

Defect in bone remodelling - osteoclasts absorb bone quicker, osteoblasts produce bone quicker The new bone is longer and weaker

Question 51

Which aspects of bone formation are of particular interest to forensics and anthropology?

Answer 51

Ossification centres, the time of appearance and the rate at which they grow

Question 52

How is bone age measured?

Answer 52

Assessing expected growth using x-ray images

Question 53

Which condition is caused by the over-secretion of GH in adulthood?

Answer 53

Acromegaly

Question 54

Where is thyroid hormone produced?

Answer 54

The thyroid

Question 55

What does thyroid hormone do?

Answer 55

Stimulates osteoblasts to promote bone growth

Question 56

Where is insulin secreted?

Answer 56

Pancreas

Question 57

What does insulin do to bones?

Answer 57

Increases synthesis of bone proteins to promote bone growth

Question 58

Example of androgen

Answer 58

Testosterone

Question 59

What do androgens do?

Answer 59

Responsible for bone strength in males

Question 60

Why are gonadal steroids important for bones?

Answer 60

Important in regulating bone growth and development of peak bone mass

Question 61

Why is oestrogen important for bone health?

Answer 61

Regulates bone formation and re-absorption | Shuts down growth at epiphyseal plate

Question 62

What is osteoporosis?

Answer 62

Osteoclasts > osteoblasts Bone mass and amount of collagen decreases Haversian canals emerge and are filled with adipose tissue

Question 63

Why does bone heal more rapidly than cartilage?

Answer 63

It has a better blood supply