W2 Bone Physiology

Question 1

what are the five basic functions of the skeleton?

Answer 1

framework and levers
protection
mineral storage
fat storage
production of blood cells

Question 2

bone is a rigid form of what?

Answer 2

connective tissue

Question 3

what is the basic unit of bone?

Answer 3

an osteon (as part of the Haversian system)

Question 4

collagen type 1 scaffold makes up about what % by weight of bone?

Answer 4

15%

Question 5

the organic matrix makes up which percentage?

Answer 5

10% by weight

Question 6

what is the major mineral component of bone?

Answer 6

hydroxyapatite (CaPO4(H2O)6)

Question 7

what does an osteogenic cell develop into (that maintains bone tissue)?

Answer 7

osteogenic cell into and osteoblast into and osteocyte

Question 8

describe where the principal bone cell, osteocytes, are found:

Answer 8

found in small spaces in the mineralised matrix called lacunae

Question 9

what connects adjacent lacunae?

Answer 9

small canals termed canaliculi

Question 10

what do osteocytes surround?

Answer 10

haversian canals

Question 11

is bone matrix impermeable or permeable to nutrients?

Answer 11

impermeable

Question 12

what do osteocytes communicate through?

Answer 12

gap junctions

Question 13

what makes up the bone cell layer?

Answer 13

periosteum, endosteum and haversian canals

Question 14

where is bone fluid found?

Answer 14

between bone cell layer and bone substance

Question 15

what do osteoblasts do?

Answer 15

synthesise and secrete collagen and other components of the cell matrix

Question 16

what is osteoid?

Answer 16

a tissue that undergoes calcification and is deposited as lamellae or layers in the bone matrix, create the foundation of bone

Question 17

calcium phosphate crystals are formed by what?

Answer 17

osteoblasts

Question 18

what do osteoclasts do?

Answer 18

they destroy bone matrix by acidifying their subcellular space to dissolve CaPO4 and enzymatically digest collagen and other matrix proteins

Question 19

what are osteoclasts derived from?

Answer 19

haemopoietic lineage

Question 20

are osteoclasts multinucleated?

Answer 20

yes

Question 21

osteoclasts have the capacity to spread over how many microns?

Answer 21

200

Question 22

what happens to the end products of degradation of osteoclasts?

Answer 22

they are absorbed into the osteoclasts before being released into the interstitial fluid

Question 23

as osteoclasts reabsorb bone, they leave behind what to encourage osteoblasts to mature?

Answer 23

mitogens (growth factors)

Question 24

osteoclasts remove damaged matrix to avoid catastrophic failure allowing what?

Answer 24

repair!

Question 25

to achieve constant mass of bone, what must be equal?

Answer 25

the amount of bone being formed must be equal to the amount of bone being removed

Question 26

what is dense bones (osteopetrosis) caused by?

Answer 26

too much activity from osteoblasts

Question 27

what causes osteoperosis?

Answer 27

too much osteoclast activity

Question 28

nutrient arteries of bones enter through what?

Answer 28

a nutrient foramen (opening)

Question 29

which part of the bone does the nutrient artery supply?

Answer 29

the inner 2/3 of the bone from the endosteum

Question 30

what supplies the outer third of the bone?

Answer 30

periosteal vessels via attachments of muscles and tendons

Question 31

describe the endosteal side of bone:

Answer 31

woven or cancellous bone housing the bone marrow, the blood supply runs parallel to the long axis in cortical bone inside Volkmanns canals

Question 32

describe the periosteal side of bone:

Answer 32

outer bone surface, also brings blood supply to the bone via soft tissue attachments

Question 33

where does ossification start in long bones?

Answer 33

starts in the middle

Question 34

the bone collar forms in the connective tissue, what does the outer layer of this eventually become?

Answer 34

vascularised periosteum

Question 35

describe the first three steps of endochondral ossification:

Answer 35

1. bones develop from structures of hyaline cartilage (which is lined with a connective tissue sheath - perichondrium) 2. ossification begins in the middle of long bones with the growth of blood vessels into the perichondrium (periosteum) 3. outer periosteum layer has dense, fibrous connective tissue, the inner layer is made up of osteoprogenitor cells. the vascularisation provides nourishment to these cells, stimulating them to differentiate to osteoblasts

Question 36

describe steps four and five of the ossification process:

Answer 36

4. the osteoblasts begin to produce osteoid, which becomes ossified and forms the bone collar 5. the bone cavity is then formed in the centre of long bones (occurs via hypertrophic chondrocytes releasing alkaline phosphatase, increasing P in the cartilage matrix) this then precipitates calcium phosphate crystals = calcification

Question 37

describe the final two steps of ossification:

Answer 37

6. blood vessels then infiltrate the centre of the calcified matrix allowing osteoclasts and osteoprogenitor cells to migrate along them, the calcified cartilage matrix is then gradually replaced by bone 7. ossification then progresses towards the ends of long bone, as osteoclasts break down tissue in the middle of the bone to form the marrow cavity

Question 38

ossification spreading from the primary centre (middle) gradually approaches what?

Answer 38

ossification spreading from secondary centres (i.e. epiphyseal growth plates)

Question 39

longitudinal growth occurs via what?

Answer 39

growth plates

Question 40

what does appositional growth allow?

Answer 40

the bone to become thicker

Question 41

what are the five zones of a growth plate?

Answer 41

1. resting/reserve 2. proliferation 3. hypertrophy/calcification 4. cartilage erosion 5. endochondral ossification

Question 42

where would you find the resting/reserve zone?

Answer 42

at the epiphyseal end

Question 43

what occurs in the proliferation zone?

Answer 43

chondrocytes form and multiply

Question 44

what happens to chondrocytes in the zone of hypertrophy/calcification?

Answer 44

they become bigger and the matrix begins to multiply

Question 45

what occurs in the zone of cartilage erosion?

Answer 45

the matrix is removed by chondroclasts and blood vessels invade

Question 46

what occurs in the zone of endochondral ossification?

Answer 46

bone replaces the removed cartilage and bone elongation occurs

Question 47

what defines the adult height of an individual?

Answer 47

growth plate closure or healing defines skeletal mature length

Question 48

roughly at what age are toy breeds skeletally mature?

Answer 48

8 months old

Question 49

roughly at what age are large/giant breeds skeletally mature?

Answer 49

14 months old

Question 50

how long does it take for cats to stop growing?

Answer 50

20-24 months

Question 51

what is intramembranous ossification?

Answer 51

when osteoblasts make bone directly within a membranous fibrous tissue structure, there are two layers that form bone between them to form two parallel plates of bone that become the to cortices of the flat bones

Question 52

skull bones and pelvic and scapular structures form in which way?

Answer 52

intramembranous ossification

Question 53

what forms an ossification?

Answer 53

selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification centre

Question 54

what happens after an ossification centre appears in the fibrous connective tissue?

Answer 54

bone matrix (osteoid) is secreted within the fibrous membrane, osteoblasts begin to secrete osteoid which is mineralised within a few days (trapped osteoblasts become osteocytes)

Question 55

between which membranes does bone form in intramembranous ossification?

Answer 55

two periosteal membranes

Question 56

does intramembranous ossification have a cartilaginous precursor structure?

Answer 56

no

Question 57

what is wolffs law?

Answer 57

the idea that bone will adapt to the loads placed upon it

Question 58

what effect does the largest applied forces have on bone?

Answer 58

trabecular struts or plates will form in orientation with the largest applied forces