introduction to the limbs

Question 1

5 functions of bone

Answer 1

support of body shape, system of levers for muscle action, protection of internal organs, site of blood cell formation, mineral storage pool

Question 2

2 bone mechanical properties

Answer 2

cable-like flexibility and resistance to tension, pillar-like stiffness and resistance to compression

Question 3

structure of bone which allows cable-like flexibility and resistance to tension

Answer 3

framework is collagen and other bone proteins (osteoid)

Question 4

structure of bone which allows pillar-like stiffness and resistance to compression

Answer 4

impregnation of collagen with crystalline mineral (hydroxyapatite - complex calcium hydroxyphosphate)

Question 5

2 main types of bone tissue

Answer 5

woven (immature), lamellar (mature)

Question 6

where is woven bone found in adults

Answer 6

earlier stages of repairing fractures

Question 7

lamellar vs woven bone

Answer 7

lamellar has lamellar layers; woven is much more irregular

Question 8

components of typical long bone, using femur as example

Answer 8

shaft (diaphysis), heads (epiphysis)

Question 9

contents and components of bone in femur head, and femur shaft

Answer 9

femur head: proximal epiphysis, spongy bone, metaphysis, medullary cavity in diaphysis, compact bone (thicker and denser), articular cartilage on end at joint; shaft: nutrient foramen for nutrient artery, hollow medullary cavity for marrow and reduce mass

Question 10

describe arrangement of lamellar bone

Answer 10

outer hard layer of compact lamellar bone (cortical bone), inner layer of interlacing struts of lamellar bone (cancellous / spongy / trabecular bone)

Question 11

describe trabecular bone

Answer 11

lamellar but irregularly arranged

Question 12

microscopy of lamellar bone

Answer 12

osteon (central canal with nerves and vessels, with concentric lamellae containing many osteocytes connected by gap junctions (share nutrients, get rid of waste), and calcium salt deposits)

Question 13

rich blood supply of bones

Answer 13

major supply is from nutrient artery through nutrient foramen/canal; arteries at epiphysis also

Question 14

what is the outer layer of bone called

Answer 14

periosteum

Question 15

2 structural features of periosteum

Answer 15

fibrous and cellular

Question 16

roles of periosteum

Answer 16

bone growth, repair

Question 17

blood and nerve supply of periosteum

Answer 17

vascular and good sensory nerve supply

Question 18

bone cell maturation pathway

Answer 18

osteogenic stem cell -> osteoblast -> osteocyte -> osteoclast

Question 19

what do osteoblasts do

Answer 19

form bone matrix

Question 20

what do osteocytes do

Answer 20

maintain bone tissue

Question 21

what do osteoclasts do

Answer 21

function in resorption and breakdown of bone matrix (targeted to prevent bone loss)

Question 22

describe border of osteoclasts

Answer 22

ruffled

Question 23

when does the skeleton form in foetal life and when does growth of some bones continue until

Answer 23

starts at 6 weeks of foetal life, and can continue until 25 years of age

Question 24

2 types of ossification

Answer 24

intramembranous, endochondral

Question 25

where is intramembrous ossification

Answer 25

in existing vascular connective tissue

Question 26

where is endochondral ossification

Answer 26

within existing foetal cartilage models

Question 27

what happens in intramembrous ossification

Answer 27

bone matrix (ostein) deposited around collagen -> mineralises to form woven bone -> remodels to lamellar bone

Question 28

what happens in endochondral ossification

Answer 28

cartilage calcifies and chondrocytes die -> periosteal osteoclasts cut channels for sprouting vessels -> osteoblasts enter with vessels to build bone round them

Question 29

intramembrous ossification

Answer 29

development of ossification centre -> calcification -> formation of trabeculae -> development of periosteum

Question 30

issue with long bones needing to support large forces while growing

Answer 30

would disrupt terminal appositional growth

Question 31

solution to preventing disruption of appositional growth in long bones while growing and supporting large forces

Answer 31

shaft ossifies first, followed by epiphyses -> growth continues by ossification at growing cartilage plate between them -> growth cessation when cartilage growth ceases and plate is over-run by ossification

Question 32

process of enochrondral ossification

Answer 32

development of cartilage model -> growth of cartilage model -> development of primary ossification centre (attracts osteoclasts) -> development of medullary (marrow) cavity -> development of secondary ossification centre -> formation of articular cartilage and epiphyseal plate

Question 33

bone elongation: epiphyseal growth

Answer 33

chondrocyte-like cells arranged in columns; continuous proliferation and elongating shaft in one direction

Question 34

age-related changes in appearance of normal bones: when do child's wrist epiphyses ossify

Answer 34

2nd year (so anytime beforehand, gaps are epiphyseal plates not fractures)

Question 35

age-related changes in appearance of normal bones: when do epiphyseal plates stop remaining cartilaginous

Answer 35

until growth ceases after puberty (so anytime beforehand, gaps are epiphyseal plates not fractures)

Question 36

4 aspects of bone adaptability

Answer 36

can grow without compromising its support functions, increases or decreases bulk and density in response to pattern of use, can alter its external and internal shape in response to pattern of use (remodelling), can repair when fractured

Question 37

3 keys to growth and remodelling of bone

Answer 37

bone has a large blood supply so cells are never far from nutrients and O2; osteocytes maintain matrix but can activate osteoblasts for new bone building; osteoclasts are giant cells specialised for destruction of bone matrix

Question 38

name and location of process of bone growing in diameter

Answer 38

apposition (addition to exterior at periosteum)

Question 39

how does bone diameter grow (apposition)

Answer 39

osteoblasts and osteoclasts create ridges and grooves on bone surface -> blood vessels align in grooves -> osteoblasts build new osteons round vessels -> osteoclasts remove bone from endosteal surface

Question 40

9 fractures of bone

Answer 40

transverse, oblique, spiral, comminuted, segmental, avulsed, impacted, torus, greenstick

Question 41

diagram of 9 fractures of bone

Answer 41

diagram

Question 42

stages of fracture healing

Answer 42

haematoma -> new blood vessels -> bony callus of spongy bone trabecula -> healed fracture

Question 43

what is an important part of fracture healing and why

Answer 43

bleeding, as haematoma becomes infiltrated by fibrous matrix and invaded by cartilage/bone progenitors

Question 44

what bone tissue is fracture repair via

Answer 44

woven (immature healing bone) tissue, which then becomes lamellar bone

Question 45

what does late fracture repair involve

Answer 45

reactive cartilage undergoing endochondrial ossification

Question 46

what happens if blood [Ca2+] levels high

Answer 46

calcitonin released by parafollicular thyroid cells -> breakdown of bone matrix by osteoclast inhibitition, and uptake of Ca2+ into bone matrix is promoted

Question 47

what happens if blood [Ca2+] levels low

Answer 47

parathyroid hormone (PTH) released by chief cells of parathyroid gland -> osteoclast bone resorption activity promoted, and increased Ca2+ reabsorption by the kidneys