Bone structure, growth and Repair

Question 1

Bone remodelling is done by which cell type?

Answer 1

Osteoclasts

Question 2

Howships lacunae are?

Answer 2

Depressions in which osteoclasts are active

Question 3

What do osteoclasts secrete and what does this secretion do? What is this process called?

Answer 3

1) Acids - digest hydroxyapitite
2) Enzymes - digest collagen

‘Decalcification’

Question 4

Focal decalcification

Answer 4

Done by organic acids

Question 5

Extracellular digestion

Answer 5

by acid hydrolysis

Question 6

Calcitonin

Answer 6

Produced by C-cells in the thyroid. A hormone that causes a DECREASE in osteoclast activity, number, movement and a decrease in membrane ruffling (so a lower SA for secretion).
Bone mass increases

Question 7

Parathyroid Hormone (PTH)

Answer 7

From the parathyroid in the neck. A hormone that INCREASES osteoblast/clast activity.

Bone mass DECREASES

Question 8

“______ can remove bone at flat surfaces”

Answer 8

Osteoclasts

Question 9

What are the three molecules that control osteoclast activity?

Answer 9

RANK (on primitive osteoclast)
RANKL (on osteoblast)
Osteoprotegerin (OTP)

OTP is a decoy molecule that stops bone reabsorbtion by ‘capping’ RANKL and stopping RANK from binding

Question 10

Formation of a Secondary Osteon

Answer 10

1) Osteoclasts drill through bone
2) Blood vessel develops and loops into the hole
3) Osteoblasts from periosteum crawl out and line the hole
4) these osteoblasts grow the hole inwards to the capillaries

Question 11

Adult bone is comprised manly of which type of osteon

Answer 11

Secondary osteon, as the original primary osteons have been replaced

Question 12

At what rate is bone replaced per year?

Answer 12

2%

Question 13

Where does growth occur often in long bones?

Answer 13

The epiphyseal plates

Question 14

what are the sites of epiphyseal growth?

Answer 14

resting cartilage/proliferation/maturation/hypertrophy/calcification/newbone

Question 15

How do the epiphyseal plate eventually stop growing?

Answer 15

The rate of cartilage growth is surpassed by the rate of bone formation, the plate fuses and epiphyseal line is left

Question 16

Steps of healing bone fractures

Answer 16

1) Hematoma (blood clot) forms,
2) Periosteum moves in and covers blood clot
3) Capillaries lag so the O2 levels are low and cells around this degenrate into chondrocytes
3) Eventually cappilaries invade, chondrocytes to osteoblasts
4) new bone is laid in a collar around the fracture site, called a ‘bone callous’
5) eventually this callous is broken down by osteoclasts, and secondary osteons invade

Question 17

why is there blood/blood clots after a fracture

Answer 17

Because there is a blood vessel in every osteon.

Question 18

What allows bone to resist tension?

Answer 18

Collagen fibres

Question 19

What allows bone to resist torsion and compression?

Answer 19

Hydroxyapitite

Question 20

What Extracellular materials are in bone?

Answer 20

Collagen fibres - resist tension
Decorin (PG) - aligns collagen fibres
Osteonectin (glycoprotein)
tissue fluid (little bit)
Hydroxyapitite

Question 21

What cells are in bone

Answer 21

Osteoblast

osteocytes

Question 22

What are the types of bones?

Answer 22

Fine Cancellous- fetal, seen via microscope
Coarse cancellous - adult
Compact Bone - solid bone

Question 23

Fine Cancellous?

Answer 23

Membrane bone (by intramembranous ossification)
- flat bones of skull. NOT preceded by cartilage, form fibrous sheets
Cartilage Bone (by endochondral ossification)
-all other bones in body. Trabeculare have core of cartilage surrounded by woven bone

Question 24

The trabeculae arrangement in Long bone

Answer 24

Arranged so the force on the head of the bone is directed down the shaft of the bone and to the surface, dispersing some of the force.

Question 25

Trabeculae arrangement in general

Answer 25

Thicker trabecaulae have a common alignment and are supported by smaller trabeculae at right angles to it

Question 26

Appositional Growth

Answer 26

Bone grows on the osteogenic surfaces. Osteoblasts secrete CF and hydroxyapitite that seeds onto bone. osteoblasts divide, daughter cell closest to the bone buries itself in matrix to become an osteocyte Remaining daughter cell will maintain the Osteogenic layer and later divide again.

Question 27

What is something that protects the osteoblasts

Answer 27

A layer of unmineralised matrix surrounding the osteoblast, giving it 'wiggle room'. This has CF but NO hydroxyapitite. This is arround osteocytes also

Question 28

What is an osteocyte process for and what does it lie in?

Answer 28

To deliver nutrients and remove waste from osteocytes. They lie in canniculi

Question 29

Why is the size of bone limited?

Answer 29

As each cell passes on nutrients whilst taking what it needs, there comes a point where not enough will be passed on = deprivation of the cell. The max width in which this will not occur in 0.2mm

Question 30

Max size of trabueculae

Answer 30

0.4mm as can only get nutrients from the peri/endosteum.

Question 31

Max thickness of compact bone

Answer 31

Much larger, due to the presense of blood vessels enclosed within the bone. On each side there is also a clear zone of vessels as the peri/endosteum can supply instead.

Question 32

What are the two ways to get a blood vessel into a bone?

Answer 32

1) Primary osteon - grows around blood vessel lying on surface 2) Secondary osteon - burrows hole by osteoclasts and vessel follows.

Question 33

Which form of osteon is more common in adults

Answer 33

Secondary as bone has stopped growing so much

Question 34

What are interstitual lamellae?

Answer 34

Bit of leftover bone from old osteons that are left from the formation of secondary osteons. they will eventually be burrowed out.

Question 35

What happens when RANK binds with RANKL

Answer 35

It acts as a signal to the primitive osteoclast to differenciate in to an active osteoclast

Question 36

High RANK, RANKL and low OPG

Answer 36

more bone reabsorbtion (bad for elderly)

Question 37

Low RANK, RANKL and high OPG

Answer 37

less bone reabsorbtion

Question 38

What experiment showed that growth didn't occur centrally in long bones?

Answer 38

Man put two holes in the centre of a chicken leg.

Question 39

What experiment discovered epiphyseal plates?

Answer 39

Man feed his pigs beetroot, stained plates red

Question 40

How could you avoid a bony calous and whats the disadvantage of this?

Answer 40

A screw and plates. Disadvantage is that this bone is weaker without the callous, more likely to fracture again