L3 Timing of Ossification and Growth Plate Fusion

Question 1

primary ossification centres of major limb bones form BEFORE/AFTER birth in all domestic mammals?

Answer 1

BEFORE

Question 2

secondary ossification centres of major limb bones are present at birth in __________ but not in ___ and ____.

Answer 2

a) Ungulates

b) Dogs and Cats

Question 3

shaping of bone during growth in response to changing mechanical loads or bone injury is known as?

Answer 3

bone MODELLING

Question 4

what are the two cellular methods by which bone modelling occurs?

Answer 4

1. through osteoblastic activity

2. through osteoclastic activity

Question 5

flat bones do not undergo interstitial growth, instead they grow through

Answer 5

apositional growth

Question 6

draw out the a flat bone and mark the surfaces for osteoblastic and osteoclastic activity

Answer 6

DRAW IT G/L

Question 7

draw out the a flat bone and mark the surfaces for osteoblastic and osteoclastic activity

Answer 7

DRAW IT G/L

Question 8

during modelling of long bone there is osteoclastic activity on the periosteal surface on the metaphysis surface, why is this?

Answer 8

to maintain metaphyseal shape

Question 9

describe the response of long bone modelling to mechanical loading

Answer 9

• stimulates formation and suppress resorption = thickening of trabeculae and/or cortex

Question 10

describe the response of long bone modelling to mechanical unloading

Answer 10

• stimulates resorption and suppress formation = thinning of trabeculae and/or cortex

Question 11

define bone remodelling

Answer 11

MAINTENANCE of adult bone through cycles of osteoclastic resorption followed by osteoblastic formation on the same surface

Question 12

describe the process of bone remodelling WITHIN cortical bone

Answer 12

• osteoclast tunnel through bone longitudinally,

- followed by osteoblasts = deposit concentric lamellae of bone to fill in the tunnel leaving space for blood vessel

Question 13

list 5 factors stimulating osteoblast activity

Answer 13

• sex steroid hormones; oestrogen, testosterone
• BMPs
• mechanical load
• inflammatory cytokines
• prostaglandins

Question 14

list 4 factors stimulating osteoclast activity

Answer 14

• parathyroid hormone
• mechanical unloading
• inflammatory cytokines
• prostaglandins

Question 15

there is no PTH receptor on osteoclasts, how are the osteoclastic activities mediated?

Answer 15

through osteoblasts - hormones and cytokines stimulate RANKL expression in osteoblasts

Question 16

list the 4 stages of cellular activity during fracture repair

Answer 16

• inflammation
• soft callus formation
• hard callus formation
• remodelling

Question 17

describe the process of inflammation within cellular activity during fracture repair

Answer 17

• formation of haematoma; due to disruption of vasc. integrity
• haematoma contains coagulation factors, attract granulocytes, lymphocytes and macrophages into haematoma
• inflam cells secrete cytokines inc. IL1, 6, FGFs, BMPs and VEGF.
• granulation tissue formed through:
• growth of capillaries into haematoma
• recruitment of mesenchymal stem cells from periosteum, bone marrow and surrounding soft tissue

Question 18

describe the process of soft callus formation within cellular activity during fracture repair

Answer 18

• mesenchymal stem cell differentiates into: chondrocytes (prolif and secrete cartilage), fibroblasts
• cell prolif and matrix production stimulated by GF’s including PDGF’s, FGFs, BMPs
• FIBROCARTILAGINOUS PLUG FORM B/W FRACTURE FRAGMENTS
• chondrocyte undergo hypertrophy, prep for vasc invasion

Question 19

during the process of soft callus formation within cellular activity during fracture repair, why is it that mesenchymal cells differentiate first into chondrocytes?

Answer 19

osteoblast differentiation requires high O2 tension // adequate vascular supply
- disrupted/fractured region = not great blood supply so chondrocyte develop first

Question 20

describe the process of hard callus formation within cellular activity during fracture repair

Answer 20

• formation of mineralised been matrix either
  REPLACING FIBROCARTILAGENOUS soft callus or where no soft callus present DIRECTLY IN FRACTURE GAP
• mesenchymal cells differentiate into osteoblasts = SECRETE BOEN MATRIX = WOVEN BONE
• high oxygen tension req.

Question 21

describe the process of callus remodelling within cellular activity during fracture repair

Answer 21

• REMODELLING OF WOVEN BONE INTO ORGINAL LAMELLAR BONE

- resop by osteoclast and replacement by osteoblast on periosteal and endosteal surfaces and within cortex.