Bone formation Flashcards
Two normal types of bone in mature skeleton
Lamellar bone
Woven bone
Two types of bone within lamellar bone
Cortical
Cancellous/ trabecular
Difference between cortical layer and trabecular bone?
Cortical= denser and makes up 80%
What is woven bone?
Immature bone made during healing and repair processes
What makes up organic paart of bone
35-40% of bone is organic
collagen I (28%)
Proteoglycans/ glycoproteins
Osteocalcin
What makes up inorganic part of bone?
Calcium hydroxyapatite
Water
What are osteoblasts
Principal bone forming cell
Stimulate osteoclast formation and activation via cell surface molecule RANKL
Where do osteoblasts originate?
Progenitor cells within osteogenic tissue of bone
What is required for osteoclast differentiation?
PTH and vitamin D receptors
What are osteocytes
Mature bone cells
What are osteoclasts
Multinucleated giant cell involved in bone breakddown
Originate from mononuclear phagocytic cells
Describe process of intramembranous ossification (5)
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
Describe steps of endochondral ossification
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
What material makes up epiphyseal growth plate?
Hyaline cartilage
What are the four zones of epiphyseal growth plate
Zone of resting cartilage
Zone of proliferating cartilage
Zone of hypertrophic cartilage
Zone of calcified cartilage
2 reasons for bone remodelling
Renews bone before deterioration
Redistributes bone matrix along lines of mechanical stress
Why is trabecular bone able to be remodelled quicker that cortical?
Larger surface area
Responds to stresses on bone quicker
How do osteocytes signal for bone remodelling?
Cellular processes extend in canliculi and touch their neighbours
surrounded by blood plasma
sense stress on bone
How do osteoclasts resorb bone?
Attach to bone, forming leak proof seal
Release enzymes and Hcl to digest collagen fibres and dissolve bone material
What happens to bone proteins and minerals durinng bone remodelling?
Cross osteoclast to exit into interstitial fluid
What happens after osteoclasts break down bone?
Osteoblasts fill lacuna with osteoid
Osteoid then mineralised
What happens when serum calcium falls?
Parathyroid glands respond by secreting parathyroid hormone
What does PTH promote?
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
How does PTH lead to reabsorption from bone?
Osteoblasts have receptor for PTH. Express RANKL. Osteoclast precursors have receptor for RANKL. Osteoclasts differentiate
What releases calcitonin
C cells in thyroid
Effect of calcitonin release?
Inhibits osteoclast reabsorption
