H07 & 08: Bone

Question 1

What are the functions of bone?

Answer 1

Protect soft tissue, support body, allow for movement, mineral storage, haematopoiesis, hormone production.

Question 2

What allows bone to be involved in haematopoiesis?

Answer 2

The presence of bone marrow

Question 3

What allows bone to protect soft tissues & support the body ?

Answer 3

The fact that it is made of rigid CT

Question 4

What allows bone to be used for movement?

Answer 4

The fact that it has articular cartilage that has no perichondrium which allows for smooth movement.

Question 5

What allows bone to be used for storage of mineral?

Answer 5

It has a lot of inorganic material.

Question 6

What is the ratio of organic material to inorganic material?

Answer 6

1:2

Question 7

What is the inorganic material that makes up bone and what are the main components of this inorganic material?

Answer 7

Inorganic material is hydroxyapatite crystals, composed of calcium & phosphorus.

Question 8

Where are osteoprogenitors found?

Answer 8

Periosteum, endosteum & cells lining Harvesian systems & Volkmann’s canals

Question 9

What do oesteoprogenitors come from?

Answer 9

Mesenchyme

Question 10

What do osteoprogenitors give rise to?

Answer 10

Osteoblasts

Question 11

Where are osteoblasts found?

Answer 11

Surface of bone

Question 12

What do osteoblasts do?

Answer 12

They produce osteoid, which is the organic component of bone.

Question 13

What do osteoblast differentiate to form?

Answer 13

Osteocytes

Question 14

Where are osteocytes found?

Answer 14

In the lacuna of bone

Question 15

What is different between osteoblasts & osteocytes?

Answer 15

Osteocytes are embedded in their own matrix and they are the fully matured and differentiated form of osteoblasts

Question 16

How do osteocytes sense stress on bone and what is this ability used for?

Answer 16

Osteocytes have dendrites so they can sense the stress on bones & send signals to other bones. They use this ability to mitigate stress on bones by regulating formation & absorption of bone.

Question 17

What is the role of osteocytes apart from sensing stress on bones?

Answer 17

Transport of metabolites & hormones between cells.

Question 18

Where do osteoclasts come from?

Answer 18

Myeloid origin

Question 19

What do osteoclasts look like?

Answer 19

They are giant, motile & multinucleated cells.

Question 20

What is the role of osteoclasts?

Answer 20

They get rid of bone.

Question 21

How do osteoclasts get rid of bone?

Answer 21

They have the enzyme collagenase that gets rid of the collagen in bone & acid that dissolves the minerals.

Question 22

How is bone resorption of bone increased?

Answer 22

Increased by parathyroid hormone that increases release of calcium

Question 23

How is bone resorption decreased?

Answer 23

Hormone calcitonin decreases release of calcium in blood and opposes the actions of PTH hormone

Question 24

Where is intermembranous bone formed?

Answer 24

In the skull

Question 25

Where is endochondral bone formed?

Answer 25

In the growth plates

Question 26

How is intermembranous bone formed?

Answer 26

Mesenchyme lays down a bone blastema that lays down woven bone

Question 27

What is intermembranous bone?

Answer 27

Primary bone

Question 28

How is endochondral bone formed?

Answer 28

A cartilage model is formed by collagen type II and bone is laid down.

Question 29

What are osteons?

Answer 29

Harvesian systems

Question 30

When are primary osteons formed?

Answer 30

When bone is initially formed

Question 31

How are osteons formed?

Answer 31

- B.v runs along surface of bone containing osteoblasts. - Bone surface invaginates. - Invagination closes with b.v in the center. - Osteoblasts produce matrix. - Osteoblasts are constantly laid down which creates lamellae.

Question 32

What is at the centre of osteons?

Answer 32

Harvesian canals

Question 33

What is at the centre of Harvesian canals?

Answer 33

Blood vessel

Question 34

State the zones of a growth plate.

Answer 34

Resting zone Proliferative zone Maturation zone Hypertrophy zone Degenerative zone Osteogenic zone

Question 35

What is the resting zone composed of?

Answer 35

Chondrocytes & hyaline cartilage

Question 36

What happens in the proliferative zone?

Answer 36

Chondrocytes undergo successive mitotic division to form columns

Question 37

What happens in the maturation zone?

Answer 37

Chondrocytes have stopped dividing.

Question 38

What happens in the hypertrophy zone?

Answer 38

Chondrocytes become vacuolated and matrix becomes calcified.

Question 39

What happens in the degenerative zone?

Answer 39

Chondrocytes senesce, leaving space for osteoprogenitors to invade.

Question 40

What happens in the osteogenic zone?

Answer 40

Osteoprogenitors differnetiate into osteoblasts & accumulate on the surface of calcified cartilage. Woven bone formation can begin.

Question 41

Where is the osteogenic zone found?

Answer 41

In the metaphysis of the bone

Question 42

Which type of collagen is found in the proliferative zone?

Answer 42

Collagen type II

Question 43

Which type of collagen is found in the hypertrophy zone?

Answer 43

Collagen type X

Question 44

How does bone increase in diameter?

Answer 44

- Osteoprogenitor cells increase in diameter. - Bone is laid down beneath the periosteum. - Osteoclasts in the medulla maintain the thickness of the bone cortex.

Question 45

What is the difference between bone modelling and bone remodelling?

Answer 45

Bone modelling is most prominent during growth & development --> allows bone to adapt to stresses. Bone remodelling involves resorption of bone & laying down new bone but the shape of the bone remains the same.

Question 46

What is the basic outline of bone remodelling?

Answer 46

Osteoclasts resorb bone & osteoblasts lay down new bone.

Question 47

What is the detailed outline of bone remodelling, with the different stages?

Answer 47

- Activation stage: where cytokines & growth factors stimulate differentiation of pre-osteoclasts. - Resorption stage: where calcified bone is resorbed. - Reversal stage: where resorption ends. - Formation stage: where osteoblasts synthesise new bone matrix. - Quiescence stage: where osteoblasts become resting bone-lining cells.

Question 48

What are the stages of repair after a fracture & what happens in each of them?

Answer 48

Inflammatory stage: haematoma forms, inflammatory cells infiltrate the area. Fibroblasts form granulation tissue & osteoclasts clear bone debris. Neovascularisation occurs. Repair stage: provisional soft callus composed of hyaline cartilage & woven bone are formed. Fracture is bridged by woven bone through endochondreal ossification. Remodelling stage: Callus is remodelled & lamellar bone is formed in response to bone use.

Question 49

How long is the inflammatory stage?

Answer 49

Days long

Question 50

How long is the repair stage?

Answer 50

Weeks to months long

Question 51

How long is the remodelling stage?

Answer 51

Length varies depending on degree of displacement, blood supply, age of patient and degree of stabilisation.

Question 52

What is the function of sesamoid bones?

Answer 52

They are used to prevent wear and tear as tendons pass over joints.

Question 53

What are splanchnic bones?

Answer 53

Bones that develop in soft tissue organs.

Question 54

What is the function of splanchnic bones?

Answer 54

They provide strength to soft tissue organs.

Question 55

What are pneumatic bones?

Answer 55

Bones with air spaces to make them lighter.

Question 56

Whaat is the function of pneumatic bones?

Answer 56

Allows for flight as they are less dense.