Bones

Question 1

Describe the structure of compact bone

Answer 1

Organised into circular structures called osteons/Haversian systems

Question 2

What structure lies in the middle of an osteon ?

Answer 2

Haversian canal

Question 3

The less dense bone is known as what?

Answer 3

Spongey (trabecular) bone

Question 4

Describe the structure of trabecular bone

Answer 4

Network of lamellate trabeculae filled with bone marrow (no Haversian systems)

Question 5

Orientation of trabeculae serves what physiology?

Answer 5

Directions of main mechanical stress

Question 6

What permeates the trabecular bone?

Answer 6

Blood vessels

Question 7

What are the names of the two membranes of bones?

Answer 7

Periosteum and endosteum

Question 8

What three specialised cell types make up bone?

Answer 8

Osteocytes, osteoblasts and osteoclasts

Question 9

What is an osteocyte?

Answer 9

Mature bone cells found in lacunae (natural depressions)

Question 10

What is the function of an osteocyte?

Answer 10

Not well understood - its suggested that they may maintain the bone matrix and sense mechanical forces

Question 11

What channels allow communication between bone cells?

Answer 11

Canaliculi connect lamellae to each other

Question 12

What is an osteoblast?

Answer 12

Immature bone cell created from osteoprogenitor cells in periosteum and endosteum

Question 13

What are the functions of osteoblasts?

Answer 13

Produces bone matrix and initiates calcification

Question 14

Unmineralised bones matrix is also known as what?

Answer 14

Osteoids

Question 15

When do osteoblasts become osteocytes?

Answer 15

When the bone matrix is fully developed

Question 16

What is an osteoclast?

Answer 16

Multinucleate cells derived from monocytes/macrophages

Question 17

Where are osteoclasts found?

Answer 17

Bone surface

Question 18

What do osteoclasts look like?

Answer 18

Large cells with ‘ruffled’ edge

Question 19

What do osteoclasts do?

Answer 19

Reabsorb bone matrix

Question 20

Where are the structure called where osteoclasts arefound?

Answer 20

Howships’ lacunae (pits on surface of bone)

Question 21

Describe the extracellular matrix of bone

Answer 21

1. 45% Hydroxyapatite crystals (complex calcium phosphate crystal)
2. 35% collagen
3. 20% water

Question 22

What is the special feature of collagen found in bone?

Answer 22

1. Modified Type I collagen fibres have strong covalent cross links which leave large gaps for hydroxyapatite crystals
2. Collagen fibre orientation linked to mechanical forces

Question 23

What two types of bone formation are there?

Answer 23

Endochondral and intramembranous

Question 24

Which is the most common type of bone formation?

Answer 24

Endochondral

Question 25

Describe the process of endochondral ossification (bone synthesis)

Answer 25

1. Bone forms a cartilage 'model' first 2. Blood vessels invade cartilage 3. Cartilage replaced with bone 4. Cartilage remains in epiphyseal growth plate - eventually ossifies

Question 26

What is the key difference between endochondral and intramembranous bone development?

Answer 26

Intramembranous bone development has no cartilaginous phase

Question 27

Describe intramembranous ossification

Answer 27

Mesenchymal cells develop osteoprogenitor cells that develop into osteoblasts that start depositing bone

Question 28

What happens to residual mesenchymal cells?

Answer 28

They develop into blood vessels and bone marrow

Question 29

Healthy bone is a balance of what processes?

Answer 29

Removal and formation

Question 30

Describe the process of bone turnover

Answer 30

1. Osteoclasts breakdown old bone 2. Osteoblasts build new bone 3. Repeat

Question 31

What are the functions of bones?

Answer 31

1. Weight baring 2. Protection 3. Mineral store 4. Blood formation

Question 32

Weight baring functions are achieved how?

Answer 32

Minerals make bone stiff (High strength under compression) and collagen gives bone flexibility and reduces risk of fracture (high tensile strength)

Question 33

Name the six types of bone

Answer 33

1. Flat bone 2. Sutural bone 3. Irregular bone 4. Short bone 5. Sesamoid bone 6. Long bone

Question 34

What is osteoporosis?

Answer 34

Occurs when the process of reabsorption is greater than the process of formation - this results in bone degradation

Question 35

Paget's Disease

Answer 35

Increased reabsorption/formation - causing massive irregularity in bone structure

Question 36

Osteopetrosis

Answer 36

Decreased reabsorption of bone

Question 37

What factors can regulate density of bone?

Answer 37

1. Weightlessness - can cause serious loss of bone density 2. Athleticism - higher bone density 3. Resistance and high impact sports are effective at maintaining bone density