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Question 1

Functions of bone

Answer 1

• Support
• load bearing
• protection (e.g. skull, ribcage)
• Attachment for muscles/levers for motion
• Storage of calcium and phosphate
• Contains bone marrow – important for haematopoiesis

Question 2

What is bone an example of

Answer 2

cONNECTIVE TISSUE

Question 3

What is structure of bone

Answer 3

, consisting of cellular component and ECM mineralised by deposition of hydroxyapatite (basic calcium phosphate)

Question 4

What is property of bone

Answer 4

is resistant to tensile (doesn’t shatter) and compressive forces

Question 5

Why has bone got good tensile strength, how to prove this

Answer 5

Collagen

Heat, denature collagen, shatter bone

Question 6

Why has bone got compressive strength, evidence

Answer 6

Hydroxyapatite crystals

Add acid, demineralise, bone becomes flexible

Question 7

Why is bone remodelling important

Answer 7

enables bone shape to be maintained during growth and allows fracture healing.

Question 8

What can fibroblast like precursor cells give rise to

Answer 8

Osteoblasts, adipocytes, myocytes, chondrocytes

Question 9

Where are osteogenic cells derived form mesenchymal tissue (undiff and pluiripotent) found in adults. Why are they needed

Answer 9

Periosteum and endosteum

Important for remodelling, growth and repair of bones by providing osteoblasts when needed

Question 10

Cells involved in bone remodelling

Answer 10

Osteoblast, osteoclast, osteocyte

Question 11

What do osteoblasts do

Answer 11

secrete osteoid – organic component of bone, initially uncalcified but rapidly becomes mineralised, as you get further away from osteoblasts, by deposition of hydroxyapatite

Question 12

When are osteoblasts recruited

Answer 12

When bone needs to grow

Question 13

What do osteoclasts do

Answer 13

bone removal– important in bone remodelling (they resorb bone), large multinucleated cells macrophages which resorb bone through acid and protease secretion, forming Howship’s lacunae which are depressions of bone surface

Question 14

What are Howship’s lacunae

Answer 14

depressions of bone surface when resorption has occurred.

Question 15

What are osteocytes

Answer 15

preserve bone matrix, sit in lacunae surrounding bony matrix

Question 16

2 types of bone formation

Answer 16

Intramembranous ossification, endochondral ossification

Question 17

Where does intramembranous ossification occur

Answer 17

Flat skull bones, mandible, maxilla, clavicle

Question 18

What is different about intramembranous ossification

Answer 18

• Bone formation from connective tissue/bone matrix (not cartilage); bone matrix produced by osteoblast

Question 19

Steps in intramembranous ossification

Answer 19

1) Osteogenic progenitor cells differentiate into (mesenchyme which differentiate into) osteoblasts forming ossification centre
2) Osteoblasts secrete osteoid which is mineralised by hydroxyapatite deposition, calcified bone engulfs osteoblasts, they are trapped in matrix becoming osteocytes
3) Spongy bone formation – trabeculae form around blood vessels, leaving pores in which red bone marrow appear later.
4) Peripheral osteoid condenses to form compact bone around spongy bone

Question 20

Sum up endochondral ossification

Answer 20

, initial hyaline cartilage that continues to grow then is calcified by chondrocytes

Question 21

Describe steps in endochondral ossification

Answer 21

• Periosteum forms around hyaline cartilage.
• Osteoblasts formed by osteogenic cells secrete osteoid on outside of cartilage, lay down bone, forming compact bony collar.
• Inner cartilage ossifies, forming primary ossification centre in diaphysis – now impermeable to nutrient diffusion so deteriorates, forming cavities
• Vessels in periosteum pass through bony collar invading inner cartilage via nutrient foramen through which osteoclasts, osteoblasts also pass.
• Remaining cartilage broken down by osteoclasts
• Osteoblasts secrete osteoid forming trabeculae (spongy bone)
• As this process continues, medullary cavity and diaphysis undergoes elongation and appositional growth.

Question 22

What’s the difference between second ossification centre and primary

Answer 22

• Spongy bone formed instead of compact
• Layer of hyaline cartilage remains on ends of long bone
• Epiphysial growth plates do not mineralise until maturity, allowing long bone growth until adulthood.
  Epiphysial plate made of cartilage, cartilage grows and divides so more cells on under side laid down and bone shaft length increases

Question 23

When does secondary ossification occur, and where

Answer 23

Just before birth, at epiphysis

Question 24

What are the different zones in growing long bone

Answer 24

1) Zone of resting cartilage
2) Zone of proliferation
3) Zone of hypertrophy
4) Zone of calcification
5) Ossified bone

Question 25

Pneumonic to remember zones of growing bone

Answer 25

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Question 26

What happens in zone of hypertrophy

Answer 26

chondrocytes mature and enlarge

Question 27

What happens in ossified bone

Answer 27

calcified cartilage on diaphyseal side of plate is replaced by bone

Question 28

What happens in resting zone of cartilage

Answer 28

cartilage attaches to epiphysis

Question 29

What happens in zone of proliferation

Answer 29

new cartilage produced on epiphysial side of plate as chondrocytes divide and form stacks of cells (all growth upwards)

Question 30

Zone of calcification

Answer 30

cartilage matrix is calcified and ossified by osteoblasts, mechanism for long bones growing.

Question 31

What happens in osteoporsis

Answer 31

: imbalance: bone breakdown>bone formation. Due to too much osteoclast activity or too little osteoblast activity. So amount of bone retained decreases

Question 32

How do bones remodel

Answer 32

- Force/stimulus to remodel – perceived by osteocyte or periosteal osteoblasts. - Osteoclasts recruited and remove unwanted bone then die - Osteoclast replaced by osteoblasts which are recruited forming new bone then becoming inactive bone lining cells - Adds new bone/makes bond stronger.

Question 33

What is appositional bone growth

Answer 33

growth or increase by the gradual accumulation of additional layers or matter . The growth in diameter of bones around the diaphysis occurs by deposition of bone beneath the periosteum.

Question 34

Role of osteoblast in appositional growth

Answer 34

secrete osteoid against the shaft of the cartilage model

Question 35

Names for spongy bone

Answer 35

Trabecular Spongy Cancellous

Question 36

2 types of secondary bone

Answer 36

Spongy | Compact

Question 37

Describe roles of spongy and compact bone in long bone

Answer 37

Spongy forms interior and epiphyses of long bones and surrounded by outer layer of denser and stronger compact bone, which forms most of outer layer of diapysis .

Question 38

Describe trabeculae of spongy bone and compact bone

Answer 38

Trabeculae of cancellous bone attached to overlying compact bone at right angles to resist compressive forces

Question 39

Describe cavities in spongy bone

Answer 39

Many interconnecting cavities

Question 40

Benefit of spongy bone

Answer 40

Forms the interior and epiphyses of long bones (so bone light enough to be moved by muscle)

Question 41

Benefit of compact bone

Answer 41

of denser and stronger compact bone, which forms most of outer layer of diapysis and provdes strength (strong cyclinders in shafts of long bone)

Question 42

Structure of spongy and compact bone in flat bones

Answer 42

Cancellous bone sandwiched between 2 plates of compact bone

Question 43

Describe primary/woven bone

Answer 43

collagen fibres in irregular arrangement with high number of osteocytes and little mineralisaton

Question 44

Where Is primary bone found

Answer 44

Tooth socket

Question 45

What happens to woven bone in adults

Answer 45

Replaced by secondary bone

Question 46

Describe secondary bone

Answer 46

- Formed as Haversian system/osteon canal along length of diaphysis - . Collagen fibres arranged in lamellae/rows. Often arranged around central canal in concentric fashion

Question 47

Where are osteocytes found in secondary bone

Answer 47

between concentric layers of lamellae in lacunae (i.e. around each layer).

Question 48

What does central/haversian canal in secondary bone contain

Answer 48

neurovascular bundle and loose connective tissue (lamellae on outside of canal)

Question 49

Why do osteocytes need cytoplasmic projections

Answer 49

Bone mineralisation prevents diffusion of nutrients and waste products. Instead osteocytes extend cytoplasmic processes into canaliculi (channels within bone containing extracellular fluid) allowing exchange of nutrients and waste products between bone and blood and communication between osteocytes.

Question 50

Describe how osteocytes are linked

Answer 50

by canaliculi and gap junctions. Projections of osteocyte connected by gap junctions form network of force sensors in canaliculi throughout the bone, connected to osteoblasts

Question 51

How can osteocyte stimulate bone remodelling

Answer 51

Projections of osteocyte connected by gap junctions form network of force sensors in canaliculi throughout the bone, connected to osteoblasts. Osteocytes can therefore communicate when force applied, sense lines of stress and stimulate remodelling to make bone stronger.

Question 52

Role of yellow and red bone marrow

Answer 52

Red bone marrow helps produce blood cells. Yellow bone marrow helps store fat.

Question 53

When do epiphysial growth plates mineralise, what's the consequence

Answer 53

Epiphysial growth plates do not mineralise until maturity, allowing long bone growth until adulthood.

Question 54

How are osteocytes formed

Answer 54

Osteocytes are simply osteoblasts trapped in the matrix that they secrete

Question 55

How does epiphysial plate allow bone shaft length to increase

Answer 55

Epiphysial plate made of cartilage, cartilage grows and divides so more cells on under side laid down and bone shaft length increases