Lecture 2 - Bone development and growth Flashcards

1
Q

what is an osteoprogenitor cell?

A

a mesenchymal stem cell derivative that differentiates into osteoblasts

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2
Q

how does the ECM become calcified?

A

by the precipitation of calcium salts such as calcium hydroxyapatite

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3
Q

ossification = ?

A

deposition of collagen + calcification

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4
Q

true or false -> calcification can occur independently of ossification

A

true

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5
Q

where can calcification occur that isnt bone as an example?

A

aging blood vessels

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6
Q

what are the two types of ossification?

A

intramembranous and endochondrial

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7
Q

briefly describe intramembranous ossification

A

bone forms directly within mesenchymal connective tissue or ‘fibrous membrane’
mesenchyme stem cells —> osteoblasts

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8
Q

which types of bones form via intramembranous ossification

A

flat bones of the skull, lower mandible and most facial bones

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9
Q

describe step 1 of intramembranous ossification

A

mesenchyme cells will move into the ossification centre and turn into osteoblasts

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10
Q

describe step 2 of intramembranous ossification

A

osteoblasts deposit osteoid and become trapped. from here the bone increases in diameter and grows outwards.

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11
Q

describe step 3 of intramembranous ossification

A

ECM develops into trabeculae that fuse to form spongy bone, trapping blood vessels in the process.

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12
Q

describe step 4 of intramembranous ossification

A

the mesenchyme at the periphery of the growing bone develops into the periosteum. bone remodelling occurs.

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13
Q

briefly describe endochondrial ossification

A

cartilage is used as an intermediate model, which is eventually replaced by bone. again, bone grows from the inside out.

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14
Q

what is the most common type of ossification in our bodies?

A

endochondrial

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15
Q

describe step 1 of endochondrial ossification

A

mesenchymal cells develop into chondroblasts which form the cartilage model

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16
Q

how does the perichondrium change to the periosteum?

A

after chondrocytes undergo hypertrophy, they encourage vascularisation, which causes blood vessels to invade the perichondrium and bring osteoprogenitor cells. stem cells begin to favour osteoblast formation, which causes the periosteum.

17
Q

where is the first change of perichondrium -> periosteum?

A

at the bone collar, where osteoblasts have just begun depositing osteoid.

18
Q

describe step 2 of endochondrial ossification

A

growth of the cartilage model by cell division of chondrocytes causes the innermost ECM to calcify due to lack of O2 and nutrients, and the innermost chondrocytes die.

19
Q

describe step 3 of endochondrial ossification

A

a nutrient artery enters the cartilage model in a small hole in the calcified ECM, which provides O2 and nutrients, which stimulates the formation of the primary ossification centre.
the nutrient artery brings osteoprogenitor cells in which eventually change into osteoblasts to begin bone formation.

20
Q

describe step 4 of endochondrial ossification

A

osteoclasts (also delivered indirectly by the nutrient artery) begin to create the medullary cavity in the diaphysis

21
Q

describe step 5 of endochondrial ossification

A

another blood vessel stimulates the formation of the secondary ossification centre in the epiphyses of the bone, which also brings in osteoprogenitor cells which will then differentiate into osteoblasts for bone formation

22
Q

describe step 6 of endochondrial ossification

A

as the secondary ossification centre grows in diameter, there is formation of the epiphyseal line and articular cartilage at the epiphysis.

23
Q

what are the articular cartilage and epiphyseal line made of?

A

hyaline cartilage

24
Q

if we can’t see an epiphyseal line, what does that tell us?

A

the patient is a full grown adult.

25
Q

what are the similarities between the two types of ossification?

A
  • both occur from mesenchymal cells
  • both begin in utero
  • involve formation of osteoblasts that secrete osteoid
  • involve blood vessel invasion
  • they are both forms of interstitial growth
26
Q

during adolescence, our bones grow in length via?

A

the epiphyseal growth plate

27
Q

how many growth plates do normal long bones have?

A

2, but the hip has three growth plates.

28
Q

what is the least stable area of the epiphysis?

A

the epiphyseal growth plate

29
Q

from epiphysis to diaphysis, name the regions of the epiphyseal growth plate

A
  • resting zone
  • proliferative zone (cells divide up and down and provide length to bone)
  • hypertrophic zone (chondrocytes secrete matrix and type X collagen which promotes calcification)
  • calcified zone
  • early bone formation (osteoblasts and osteoclasts come in)
30
Q

which direction does bone grow in length?

A

towards the epiphysis

31
Q

what is the epiphyseal growth plate aka?

A

the physis