Bone: structure growth and repair

Question 1

Compact bone

Answer 1

Around the outsides of bone.

Question 2

Coarse cancellous bone

Answer 2

Adult spongy bone

Question 3

Fine Cancellous bone

Answer 3

Fetal bone. Cancellous means spongy.

Question 4

Trabeculae

Answer 4

Small elements in lamaller bone (adult coarse cancellous or stingy bone)

Question 5

Why is bone good under tension

Answer 5

It contains a lot of collagen

Question 6

Why is bone good under pressure and torsion

Answer 6

Hydroxapatite

Question 7

Components of bone

Answer 7

Collagen and hydoxyapatite. Very little proteoglycan

Question 8

Periosteum

Answer 8

Fibrous layer on the surface of bone that contains osteoblasts that generate new bone

Question 9

Endosteum

Answer 9

Surface of cancellous bone and inner surface of compact bone with similar properties to the periosteum

Question 10

Cells in bone

Answer 10

Osteoblast (immature)

Osteocyte (mature)

Question 11

Fibre(s) in bone

Answer 11

Collagen

Question 12

Proteoglycan matrix in bone

Answer 12

Decorin

Question 13

What does decor do

Answer 13

Holds the collagen fibres together

Question 14

Glycoproteins in bone

Answer 14

Osteonectin (bind components of matrix together)

Question 15

What is the mineral in bone

Answer 15

Hydroxyapatite. Allows the bone to withstand compression and torsion

Question 16

Describe membrane bone

Answer 16

A kind of fine cancellous (fetal bone). Forms from osteoblasts in flat sheets creating the flat bones of the skull

Question 17

Describe cartilage bone

Answer 17

A kind of fine cancellous bone (fetal bone) formed from cartilage creates most bones in the body.

Question 18

Describe woven bone

Answer 18

Fetal fine cancellous bone. Called woven as the collagen fibres are not yet arranged in parallel.

Question 19

How does fine cancellous bone (woven bone) turn into adult bone (lamellar bone)

Answer 19

Turns into coarse cancellous (spongy) and compact bone. It becomes lamellar bone when collagen fibres are laid down in alternating parallel sheets. Happens gradually.

Question 20

Where are osteoblasts found

Answer 20

On the surfaces of bone in the osteogenic layers, either periosteum or the endosteum

Question 21

How is the periosteum attached to the bone

Answer 21

Through collagen fibres at right angles to the bone known as sharpy’s fibres

Question 22

Describe the growth of bone

Answer 22

Grows at the periosteal and endosteal surfaces. Osteoblasts divide and the progeny away from the bone surface remains in the periosteum or endosteum and divide again. The other progeny secretes new bone matrix. Called appositional growth

Question 23

Appositional growth

Answer 23

Means applying something (bone) to a surface

Question 24

When do osteoblasts become osteocytes

Answer 24

Once they divide and secrete matrix and have surrounded themselves with hydroxyapatite

Question 25

What do osteoblasts secrete

Answer 25

Collagen fibres and hydroxyapatite and other matrix components

Question 26

How do osteocytes obtain their nutrition

Answer 26

Osteocytes have cell processes which run in small channels called canaliculi. Each cells passes on nutrients to its neighbour which in turn passes its nutrients to its neighbour. Nutrition comes from the endosteum or periosteum

Question 27

How far can nutrients be passed before the last cell in the chain suffers from deprivation

Answer 27

0.2 mm. Therefore maximum thickness of trabeculea is 0.4mm (pass from both surface). This is why blood supply has to exist in compact bone which is thicker than 0.4 mm

Question 28

How do blood vessels get inside the bone?

Answer 28

1. They are enclosed at the surface during appositional growth (primary) 2) They invade channels in bone formed by osteoclasts (secondary)

Question 29

Two forms of osteon formation

Answer 29

Primary (appostional) formation where periosteum surrounds blood vessels and becomes endosteum which lays down bone in towards blood vessel. Secondary

Question 30

What is the canal in the middle of the osteon called

Answer 30

Havasian canal

Question 31

What are the canal the run perpendicular to the osteon that hols capillaries that feed into the havarsian canals called

Answer 31

Volkmans canals

Question 32

What are the canal the run perpendicular to the osteon that hols capillaries that feed into the havarsian canals called

Answer 32

Volkmans canals

Question 33

How does bone remodelling occur?

Answer 33

Through removing bone from the inside and adding bone on the outside. This occurs through osteoclasts derived from blood cells.

Question 34

How do osteoclasts work

Answer 34

Osteoclast seals onto bone with 'collar'. In the basolateral membrane of the osteoclast is a ruffled border. Within the border are vesicles holding acids and enzymes. Acids digest hyroxapatite, enzymes digest the collagen.

Question 35

Hormonal control of bone removal

Answer 35

Parathyroid hormone- increases osteoblast and osteoclast activity, decreases bone mass. Calcitonin- reduces osteoclast activity

Question 36

Describe the interplay between RANK and RANK-L

Answer 36

RANK is a molecule found on primitive osteoclasts. RANK-L is found on mature osteoblast. When RANK-L binds to RANK this signals the primitive osteoclast to differentiate and become mature.

Question 37

What does OPG do

Answer 37

OPG- osteoprotegrin. Acts to block RANK-L binding to RANK. Inhibits bone loss

Question 38

Why does decreasing oestrogen levels cause osteoperosis

Answer 38

Oestrogen reduces the activity of osteoclasts through decreasing RANK L levels

Question 39

What does HRT do

Answer 39

Reduces the activity of osteoclasts, less bone reabsorption

Question 40

Is most adult bone composed of primary or secondary osteons?

Answer 40

Secondary

Question 41

At what rate is bone replaces each year?

Answer 41

2%

Question 42

What are the three molecules that control osteoclast activity

Answer 42

RANK, RANK-L and OPG

Question 43

Where does growth in long bones occur

Answer 43

Epiphyseal plates

Question 44

Describe the process of long bones growing in length

Answer 44

In youth there are epiphyseal plates which grow cartilage at one end which at the other end the cartilidge dies and blood vessels bring in osteoblasts and bone forms this occurs until closure of the epiphyseal plates during/ after puberty.

Question 45

How do bone fractures heal

Answer 45

The periosteum and endosteum provide osteoblasts which secrete bone cells in a collar around the fracture site. Later osteoclasts dig out channels and new secondary osteons to knit together fracture

Question 46

What are the stages of growth in growth in length of a long bone

Answer 46

``` From the epiphyses side of cartilage: Zone of resting Zone of proliferation Zone of maturation Zone of ossification ```

Question 47

What is a howships lacunae

Answer 47

The space around the osteoclast on the surface of the bone.