Bone formation

Question 1

Two normal types of bone in mature skeleton

Answer 1

Lamellar bone

Woven bone

Question 2

Two types of bone within lamellar bone

Answer 2

Cortical

Cancellous/ trabecular

Question 3

Difference between cortical layer and trabecular bone?

Answer 3

Cortical= denser and makes up 80%

Question 4

What is woven bone?

Answer 4

Immature bone made during healing and repair processes

Question 5

What makes up organic paart of bone

Answer 5

35-40% of bone is organic
collagen I (28%)
Proteoglycans/ glycoproteins
Osteocalcin

Question 6

What makes up inorganic part of bone?

Answer 6

Calcium hydroxyapatite

Water

Question 7

What are osteoblasts

Answer 7

Principal bone forming cell

Stimulate osteoclast formation and activation via cell surface molecule RANKL

Question 8

Where do osteoblasts originate?

Answer 8

Progenitor cells within osteogenic tissue of bone

Question 9

What is required for osteoclast differentiation?

Answer 9

PTH and vitamin D receptors

Question 10

What are osteocytes

Answer 10

Mature bone cells

Question 11

What are osteoclasts

Answer 11

Multinucleated giant cell involved in bone breakddown

Originate from mononuclear phagocytic cells

Question 12

Describe process of intramembranous ossification (5)

Answer 12

1) mesenchymal cells differentiate into osteoblasts form ossification centre
2) osteoblasts secrete bone matrix which starts to mineralise (trapped osteoblasts become cytes)
3) vascularised mesenchyme outside ossification centre forms periosteum
4) bone deep to periosteum hardens into bone collar
4) remodelling takes place to form compact and trabecular bone

Question 13

Describe steps of endochondral ossification

Answer 13

1) periosteal bud invades, brings osteoblasts into centre
2) capillaries grow into cartilage model
3) primary ossification centre grows towards ends
4) osteoclasts remove woven bone forming cavity
5_ blood vessels grow into epiphyses and form secondary ossification centres
6) Hyaline cartilage remains at end

Question 14

What material makes up epiphyseal growth plate?

Answer 14

Hyaline cartilage

Question 15

What are the four zones of epiphyseal growth plate

Answer 15

Zone of resting cartilage
Zone of proliferating cartilage
Zone of hypertrophic cartilage
Zone of calcified cartilage

Question 16

2 reasons for bone remodelling

Answer 16

Renews bone before deterioration

Redistributes bone matrix along lines of mechanical stress

Question 17

Why is trabecular bone able to be remodelled quicker that cortical?

Answer 17

Larger surface area

Responds to stresses on bone quicker

Question 18

How do osteocytes signal for bone remodelling?

Answer 18

Cellular processes extend in canliculi and touch their neighbours
surrounded by blood plasma
sense stress on bone

Question 19

How do osteoclasts resorb bone?

Answer 19

Attach to bone, forming leak proof seal

Release enzymes and Hcl to digest collagen fibres and dissolve bone material

Question 20

What happens to bone proteins and minerals durinng bone remodelling?

Answer 20

Cross osteoclast to exit into interstitial fluid

Question 21

What happens after osteoclasts break down bone?

Answer 21

Osteoblasts fill lacuna with osteoid

Osteoid then mineralised

Question 22

What happens when serum calcium falls?

Answer 22

Parathyroid glands respond by secreting parathyroid hormone

Question 23

What does PTH promote?

Answer 23

1) Ca2+ resorbtion from kidney and PO4 excretion
2) Synthesis of vitamin D3 by acting on converting enzymes in kidney. D3 increased calcium absorption in gut
3) Ca2+ reabsorption from bone: more osteoclasts

Question 24

How does PTH lead to reabsorption from bone?

Answer 24

Osteoblasts have receptor for PTH. Express RANKL. Osteoclast precursors have receptor for RANKL. Osteoclasts differentiate

Question 25

What releases calcitonin

Answer 25

C cells in thyroid

Question 26

Effect of calcitonin release?

Answer 26

Inhibits osteoclast reabsorption