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MSK Week 4 > ICL 5.2: Bone Growth & Development > Flashcards

ICL 5.2: Bone Growth & Development Flashcards

1
Q

what are the two types of bone formation?

A

bone development = bone formation = ossification

the type of bone formation is based on the type of tissue in which ossification is occurring

  1. intramembranous ossification
  2. endochondral ossification
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2
Q

what is intramembranous ossification? where does it occur in the body?

A

it occurs within highly vascular mesenchymal tissue –> mesenchyme cells are pluripotential and differentiate into osteoprogenitor cells

then the mesenchymal/osteoprogenitor cells group together and the cells become larger and make cellular contact with adjacent cells

the bone forms within fibrous connective tissue membrane

ex. in the mesenchyme in developing embryo or fetus

it occurs in flat bones of skull and face: frontal, parietal, maxilla, palatine, lacrimal and nasal bones; and sternum

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3
Q

what is endochondral ossification? where does it occur in the body?

A

it occurs within hyaline cartilage model of bone –> cartilage is removed and replaced with bone tissue

it occurs in most bones of the body and some skull bones (ethmoid, sphenoid, and zygomatic)

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4
Q

what is the difference between encochondral and intramembranous ossification?

A

nothing! the type of bone formation is based on the type of tissue in which ossification is occurring

there’s no difference in the bone tissue formed in either type; both types of ossification lay down identical bone tissue
= woven bone

there is NO structural difference between bone tissue laid down by intramembranous or endochondral ossification

ALL bone growth is appositional growth

bone tissue is formed the same way in both types of ossification:

osteoprogenitor cells differentiate into osteoblasts –> osteoblasts lay down new osteoid on surface –> mineralization of osteoid occurs and osteoblasts become osteocytes

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5
Q

what are the steps in intramembranous ossification?

A
  1. mesenchyme cells differentiate into osteoprogenitor cells
  2. mesenchymal/osteoprogenitor cells group together and get larger and make contact with adjacent cells
  3. osteoblasts secrete osteoid on the mesenchymal surface
  4. mineralization of osteoid
  5. small bone island is formed; each island is formed equidistant from surrounding blood vessels
  6. mineralization is occurring and osteoblasts are becoming osteocytes
  7. the next generation of osteoblasts differentiate on the surface so that they can lay down the next layer of osteoid

the individual islands are increasing in size by appositional growth

  1. separate islands enlarge until they fuse to form trabecula
  2. trabecula continue to enlarge and connect with other trabecula to form network of trabecula –> this is how trabecular bone (spongy, cancellous) is first formed
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6
Q

what is compaction?

A

the process of forming compact bone from trabecular bone

it occurs through the continuous deposition of additional layers of osteoid and osteoblasts on the surface

the edges of adjacent trabecula meet to form primitive osteon –> this osteon is composed of woven bone (but it may have concentric rings of osteocytes like definitive osteon of lamellar bone)

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7
Q

what type of bone is your skull and what does it turn into?

A

flat bones of the skull are spongy bone until 8 years old

then they remodel into inner and outer tables of compact bone with spongy bone left in-between

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8
Q

what is an ossification center?

A

the place where ossification starts in an individual bone

the ossification process starts in center and radiates out towards the periphery of the forming bone –> so that means the oldest and most developed bone will be located in the middle

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9
Q

when does ossification of the skull start in utero?

A

first trimester

parietal bone - 7th wk of gestation

frontal bone - 8th wk of gestation

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10
Q

when during life do you see endochondral ossification?

A

endochondral ossification occurs in pre-existing model of bone composed of hyaline cartilage

it’s observed in 2 places:

  1. during initial development of bones in fetus
  2. in epiphyseal plate of young child or adolescent
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11
Q

explain the endochondral ossification that occurs during initial development of bones in fetus

A

endochondral ossification occurs within a hyaline cartilage model of long bone

  1. the first change occurs mlidshaft as hypertrophy of chondrocytes

the cells secrete alkaline phosphatase (AKP) which raises Ca+2 and PO4(-3) levels –> this causes the cartilage matrix to calcify and the chondrocytes start to die as nutrient flow is cur off by the deposition of minerals

  1. at the same time, perichondrium becomes active (vascularized)

osteoprogenitor cells differentiate into osteoblasts and osteoid is laid down and mineralized in fibrous perichondrium

osteoid forms the periosteal bone collar around the midshaft of the cartilage model via intramembranous ossification within the perichondrium

  1. invasion of the periosteal buds from the periosteum through the collar holes into the cartilage matrix

small periosteal buds erode away uncalcified cartilage matrix but don’t disturb the trabecula of calcified cartilage matrix

the periosteal buds bring in osteoprogenitor cells which migrate across the cavity to the surface of calcified cartilage matrix remnants

the osteoprogenitor cells differentiate into osteoblasts that lay down osteoid

osteoid undergoes calcification and then the next generation of osteoblasts lays down more bones matrix

  1. trabecula are formed on the remnants of calcified cartilage and they produce a medullary cavity of spongy bone

the formed bone is woven bone –> the next step is trabecular remodeling

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12
Q

where does ossification start in a long bone?

A

at the center of the diaphysis (shaft)

it then proceeds towards both ends of the long bone

this movement can be used clincally to determine bone age of small babies

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13
Q

what is the epiphyseal plate?

A

a band of hyaline cartilage located between the diaphysis and epiphysis

it’s the place where endochondral ossification occurs!

it’s the exact same process as you see in fetuses initially but now it’s just organized into zones

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14
Q

what are the 5 zones of endochondral ossification in adolescents?

A
  1. zone of reserve cartilage/resting zone
  2. zone of proliferation
  3. zone of hypertrophy
  4. zone of calcification
  5. zone of ossification
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15
Q

what is the zone of reserve cartilage?

A

one of the 5 zones of the epiphyseal plate

  1. located nearest epiphysis
  2. normal hyaline cartilage
  3. attaches cartilage to bone
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16
Q

what is the zone of proliferation?

A

one of the 5 zones of the epiphyseal plate

  1. proliferating chondroblasts
  2. column of flattened cells
  3. isogenous group
  4. interstitial growth

this zone is key to plate function!

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17
Q

what is the zone of hypertrophy?

A

one of the 5 zones of the epiphyseal plate

the cells increase in size and so does the matrix

secretion of ALP is happening here too

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18
Q

what is the zone of calcification?

A

one of the 5 zones of the epiphyseal plate

this is where mineralization of cartilage matrix happens

the last two rows of hypertrophied cells die

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19
Q

what is the zone of ossification?

A

one of the 5 zones of the epiphyseal plate –> this zone is split into primary and secondary spongiosa

  1. blood vessels invade
  2. dead chondrocytes and uncalcified cartilage matrix are eroded
  3. osteoprogenitor cells with blood vessels migrate to exposed surface of calcified cartilage matrix that’s left
  4. osteoprogenitor cells differentiate into osteoblasts and lay down bone osteoid
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20
Q

what is the zone of primary ossification?

A

it’s the first part of the zone of ossification at the epiphyseal plate

once the osteoid is calcified, woven bone is deposited

then trabecula are formed longitudinally followed by spongy bone

this spongy bone formed is called primary spongiosa/zone of primary ossification

21
Q

what is the zone of secondary ossification?

A

it’s the second part of the zone of ossification at the epiphyseal plate

this is the “6 th zone” and isn’t actually part of the plate

this is where internal/trabecular remodeling happens and woven bone gets replaced with lamellar bone

22
Q

what is the function of the epiphyseal plate?

A

to increase the length of long bone

proliferation and interstitial growth add more cartilage on the epiphyseal side of the plate while simultaneously cartilage is removed and replaced with bone on the diaphyseal side

the net effect is increased length of the bone while the thickness of the plate remains the same!!!

23
Q

when does the epiphyseal plate close?

A

normally, in growing child there is a balance between proliferation of cartilage and erosion – closure is initiated when balance is changed

late in adolescence, the rate of proliferation slows while the rate of erosion is constant

this means that the plate slowly erodes away until there is no longer a proliferation zone

on x-rays, you’ll see a white line that indicates epiphyseal line closure

24
Q

when does the epiphyseal plate close in long bones and in the skull?

A

long bones = mid 20’s

base of the skull = mid 30s

25
Q

which substances influence the epiphyseal plate?

A
  1. sex hormones
  2. growth hormone
  3. vitamin A
  4. vitamin D
  5. vitamin C
26
Q

how do sex hormones effect the epiphyseal plate?

A

androgen & estrogen stimulate bone formation

aka they accelerate closure of the plate!

so since puberty is earlier in females, this is why their epiphyseal plate closes earlier and they stop growing earlier

27
Q

how does growth hormone effect the epiphyseal plate?

A

GH is secreted by the anterior pituitary gland and stimulates the cartilage growth in the epiphyseal plate

so it makes your bones longer!

28
Q

what is pituitary gigantism?

A

GH is secreted by the anterior pituitary gland and stimulates the cartilage growth in the epiphyseal plate

so pituitary gigantism is excess GH in a growth child and causes them to grow a ton

29
Q

what is dwarfism?

A

GH is secreted by the anterior pituitary gland and stimulates the cartilage growth in the epiphyseal plate

dwarfism is a deficiency of GH in a child

30
Q

how does vitamin A effect the epiphyseal plate?

A

vitamin A balances bone deposition with bone resorption aka it coordinates activity between osteoblasts and osteoclasts

excessive vitamin A leads to more rapid erosion and leads to early closure = dwarfism

vitamin A deficiency means slower/lack of erosion and a slower growth rate at the epiphyseal plate which causes the internal organs to grow faster than the bones….this means that things like the cranial cavity and spinal cord won’t have enough space to grow and this could lead to retardation and possible death

31
Q

how does vitamin D effect the epiphyseal plate?

A

vitamin D controls the normal absorption of Ca+2 from the gut

so if there’s a vitamin D deficiency, there won’t be enough Ca+2 which will lead to no mineralization of the cartilage in the bone osteoid

aka bones will lack strength and have an enlarged zone of hypertrophy

this causes the bending of leg bones as the body gets heavier = bow legs!!!!

32
Q

what is osteomalacia?

A

adult rickets

aka a deficiency of vitamin D in adults

33
Q

how does vitamin C effect the epiphyseal plate?

A

vitamin C is a co-factor of hydroxylation of proline in forming alpha chains of procollagen

so without vitamin C, a lack of H+ bonding between alpha chains results in weak collagen I –> weak collagen in osteoid means weak bones!

all of this results in thin cortical bone and a slow repair of fractures and bone development

34
Q

what is bone modeling?

A

the process of maintaining and shape and proportions of a bone as it increases in size

35
Q

how does long bone modeling work?

A

in the conical region, wide epiphysis must be trimmed down to narrow diaphysis as length is increased

at the top of the cone, bone is resorbed on the outside by osteoclasts

then the bone is deposited on the outside of the cortical bone by osteoblasts while osteoclasts resorb bone on the inside surface of the cortical bone

this way, the cortical bone maintains its thickness but the overall diameter of the bone is increased

36
Q

how does flat bone modeling work?

A

there is bone deposition at the ends of the bones along suture lines

then there is bone resorption on the inner surface of the tableau

this way the thickness is maintained the same but the tableau is shifted outward

37
Q

what is a simple fracture?

A

broken bones remain in the

body and do not open the skin

38
Q

what is a compound fracture?

A

broken bones penetrates through the skin and exposure to the outside

39
Q

what is a reduction of a fracture?

A

when two fragments are moved back into proper alignment

40
Q

what is a direct trauma of a bone?

A

broken osteons, torn periosteum, hematoma formation, swollen, painful (3- 4 hrs)

41
Q

what is an indirect trauma?

A

due to interrupted BV’s, no nutrients/O2 and osteocytes die

42
Q

what are the steps in a fracture repair that your own bones do?

A
  1. early repair
  2. external callus formation
  3. internal callus formation
  4. joint callus formation
  5. union

6.

43
Q

what is the early repair stage of fracture repair?

A

neutrophils & macrophages start cleaning up blood clot by phagocytosis

then granulation tissue starts to form and the clot is replaced by granulation tissue

this happens during the first 1-7 days following a fracture

44
Q

what is a callus?

A

callus
a callus is a mass of tissue forms and connect
the broken ends of the bone, stabilizes the fracture

formation begins around the bone fragments 3-4 weeks after injury

pain and swelling decrease

45
Q

what is an external callus?

A

you can palpate as a lump on the bone!

osteoprogenitor cells in the periosteum migrate to the fracture site then differentiate into osteoblasts and lay down osteoid

there are also osteoprogenitor cells that differentiate into chondroblasts and form hyaline cartilaginous callus directly on existing bone fragment

46
Q

what is an internal callus?

A

it’s smaller than the external callus and arises from osteoprogenitor cells in the endosteum which proliferate and differentiate into osteoblasts

mesenchymal cells closer to the fracture gap differentiate into fibroblasts or chondrocytes which form a fibrous cartilage callus that grows towards the opposite fragment!

the internal callus is formed on the inside of the marrow cavity and between the bone fragments

47
Q

what is bone union?

A

when calluses from each fragment meet and fuse together

  1. fibrous union = when fibrous tissue from two fragments meet
  2. cartilaginous union = when cartilage of the two fragments fuse
  3. bone union = when forming bone trabecula from each fragment fuse together

in fractures with large gaps then callus will have mixture of fibrous, hyaline cartilage and spongy bone

48
Q

what happens overall during the process of fracture repair?

A

both intramembranous & endochondral ossification occur

woven bone is laid down first then internal remodeling and trabecular remodeling removed woven bone and replaces it with lamellar bone

remodeling & modeling slowly reduces callus

it takes about 6-8 weeks to get a good bony union

MSK Week 4 (11 decks)

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