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Bloc H - Movement > May24 M1-Histo 3 > Flashcards

May24 M1-Histo 3 Flashcards

1
Q

def of bone remodelling

A

balance between

  • bone adding by osteoblasts
  • bone resorption by osteoclasts
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2
Q

balance of bone remodelling during skeletal growth

A

bone deposition exceeds bone resorption

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3
Q

balance of bone remodelling during adulthood

A

bone deposition = bone resorption

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4
Q

balance of bone remodelling during during old age

A

bone resorption exceeds bone deposition. this also occurs earlier in osteoporosis

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5
Q

end result of bone resorption exceeding bone deposition

A

loss of skeletal mass

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6
Q

what induces bone remodelling

A

fatigue damage in the bone. resulting in these events:

  • accumulation of microcraks in the mineralized ECM
  • osteocytes mechanosensory network senses this damage
  • osteocytes signal for bone remodelling to replace these microcracks with new bone
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7
Q

why bone remodelling is needed to repair microcracks

A

too many microcracks lead to bone fracture

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8
Q

skeletal cell types involved in bone remodelling and in initiating it

A
  • initiated by osteoclasts

- involves all cell types

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9
Q

2 mechanisms of bone remodelling

A
  • stochastic process (random): prevent bone age from exceeding an acceptable level. = random bone replacmeent
  • directed process: removes bone that is in some way defective from a specific location (OSTEOCYTES SENSING MICROCRACKS AND REPLACING DEFECTIVE PARTS)
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10
Q

in the adult skeleton, what creates the demand for osteoblasts

A

bone resorption

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11
Q

in the adult skeleton, what creates the demand for osteoclasts

A

the different purposes of bone remodelling

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12
Q

what allows growth of long bones during endochondral bone formation (endochondral ossification)

A

cartilage. it persists in
- articular surface (hyaline cartilage and perichondrium)
- epiphyseal plate (perichondrium on both sides so will be persistent perichondrium, the one responsible for bone growth)

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13
Q

what happens to woven bone in the diaphysis of long bones during development

A

developmental remodelling

  • woven bone is replaced by compact lamellar bone (the epiphyseal plate is responsible for this growth in length)
  • during adulthood, growth continues as a radial growth
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14
Q

why woven bone in diaphysis of long bones initially (first in development)

A

bcause first step in endochondral bone formation is intramembranous ossification

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15
Q

longitudinal growth vs radial growth of bone

A
  • longitudinal growth = on bone length

- radial growth = on bone diameter (deposition on periosteal surface and resorption on endosteal surface)

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16
Q

4 stages of RADIAL growth of the diaphysis of long bone

A
  • early foetal life (formation of woven trabecular bone)
  • late foetal life (last step where you see woven trabecular immature bone with disorganized collagen)
  • childhood
  • adulthood
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17
Q

composition of bone in early and late fetal life + where osteoblasts and osteocytes are found in this bone

A
  • trabecules of primary bone only (woven) formed by periosteal intramembranous ossification
  • osteoblasts on periphery of the trabecules
  • osteocytes within the trabecules
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18
Q

in early and late fetal bone, what is between the trabecules

A

CT and blood vessels

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19
Q

early and late fetal bone origin + structure

A

trabecules + CT lined on one side by periosteum (the origin of this intramembranous ossification) and on the other side by endosteum definitive, organizing endosteum.

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20
Q

diff things happening to bone between late foetal life and childhood

A
  • woven bone replaced by lamellar bone
  • Volkman’s canals penetrate through the periosteum and and get through the endosteum
  • Volkman’s canals have blood vessels and osteoprogenitor cells, osteoblasts and osteoclasts with them
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21
Q

how can Volkman’s canal tunnel through the bone as you transition into childhood

A

bone resorption

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22
Q

what do Volkman’s canals do after they penetrated through woven bone perpendicularly

A
  • will eventually turn 90 degrees and follow the direction of bone
  • this creates big cavities occupied by osteoclasts
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23
Q

cells that Volkman’s canals (and anything penetrating through endostium and periostium) bring with them

A
  • osteoprogenitor cells
  • osteoblasts
  • osteocytes
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24
Q

what happens to cavities created by Volkman’s canals in woven bone of late foetal life

A

replaced by lamellar bone and Haversian systems. these will replace woven bone

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25
Q

histology of bone in childhood

A
  • concentric bone lamellae (Hav systems) formed in spaces between the woven bone trabecules
  • primary bone progressively disappears because of OSTEOCLASTS
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26
Q

histology of COMPACT bone in adulthood

A
  • is lamellar bone only

- this lamellar bone is constantly restructured by dissolution and replacement of osteons (by osteon reconstruction)

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27
Q

example of pattern you may expect to see in adult compact bone

A
  • some big canals originating from Volkman’s canal turning and following bone length eventually
  • these canals had osteoblasts which produced all the lamellar bone.
  • this concentric production of lamellar bone by osteoblasts near the canal creates Haversian systems
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28
Q

charact of immature Haversian system

A
  • wider middle canal
  • surrounded by dividing osteoblasts which produce ECM and lamellar bone
  • osteocytes getting trapped between the lamella
  • osteoblasts and osteocytes continue to grow towards the center and system being formed layer by layer
  • the Haversian canal is becoming smaller with less vessels in it
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29
Q

charact of mature Haversian system

A
  • small Hav canal with one only blood vessel (capillary) in it for nutrition
  • a cementing line surrounding the Hav system is produced (seals the whole thing)
  • divison of osteoblasts, grow to the center, formation of Hav system and lamella
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30
Q

when does the formation of the circumferential lamellae occur

A

near the end of skeletal growth

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31
Q

how formation of circumferential lamellae occurs

A
  • periosteum adds sheets of bone wrapping outside
  • they have the form of concentric lamellae that encircle the bone (and surround the compact Hav bone layer (cortical bone))
  • surrounding = outer circumferential lamellae
  • endosteum does the same thing to do the inner circumferential lamellae
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32
Q

at the end of skeletal growth, what happens to the central mixed spicules formed by endochondral ossification and that are present near the metaphysis and the epiphysis

A
  • remodeled to form a spongy trabecular cancellous bone network with trabecules (spicules) of lamellar bone only with no cartilage core (initially had core remnant from growth plate)
  • this bone replaces the cartilaginous epiphyseal plate to make an EPIPHYSEAL SCAR that persists in adult bone
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33
Q

in the adult bone, where do you find hyaline cartilage

A

ONLY at the extremities of the bone as articular cartilage

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34
Q

directions of bone growth and shaping after late fetal life in the epiphyseal plate

A
  1. growth in length (chondrogenesis)
  2. radial growth at the level of the metaphysis (due to addition of hyaline cartilage to the perichondrium). funnel formation.
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35
Q

what is the cause of growth in length in epiphyseal plate at end of fetal life

A
  • addition of chondrocytes in epiphyseal plate
  • cells dividing at the epiphyseal plate and pushing the epiphysis of the bone out of the way
  • chondrogenic activity*
36
Q

in late foetal life, 3 things happening in bone in the METAPHYSIS at the same time as the growth in length + radial growth of the epiphyseal plate

A
  • osteoblasts add bone on endosteal (inner) surface
  • osteoclasts resorb bone on the periosteal surface (remodelling of the funnel)
  • formation of new spicules by lateral invasion of blood vessels (MAKES TRABECULAR BONE)
37
Q

what do we mean by remodelling of the funnel by osteoclasts (removing bone in periosteum) and by funnel formation (from hyaline cartilage addition from perichondrium for radial growth at epiphyseal plate)

A

funnel = the part of the bone where the epiphysis and metaphysis (head) becomes narrower to transition into the less thick epiphysis (shaft). funnel = the curve there where the bone becomes less wide

38
Q

what is responsible for the funnel shape of the bone (not a tube but rather a shaft which is less wide than the heads)

A

osteoclastic activity right under the periosteum at the level of the metaphysis

39
Q

how the formation of new spicules in bone metaphysis at end of fetal life by lateral invasion of blood vessels occurs

A
  • these blood vessels are bringing in osteoblasts

- these osteoblasts form the mixed spicules (TRABECULAR BONE)

40
Q

consequence of formation of new spicules in bone metaphysis at end of fetal life by lateral invasion of blood vessels

A

the bone finds support to push the epiphysis away from the center (bc this happens most superficially in the metaphysis, near bone surface) where spicules can be SUPPORTED ON ENDOSTEUM UNDER THE EPIPHYSEAL PLATE

41
Q

consequence of osteoblasts adding bone on endosteal (inner) surface of metaphysis

A

endosteal surface (endosteal zone) gets thicker

42
Q

diff layers of the periosteum at the level of the metaphysis (when periosteum is being remodelled by osteoclasts to make the funnel shape)

A
  • fibrous periosteum
  • osteogenic periosteum underneath
  • layer of multinucleated cells (osteoclasts) underneath the osteogenic periosteum
43
Q

during bone dev at end of fetal life, what happens in the diaphysis + what happens to the bone spicules previously there

A

opposite of metaphysis

  • osteoclastic activity on endosteal surface
  • osteogenesis on periosteal surface
  • this results in radial, lateral growth of bone and in a bigger cavity of marrow*
  • when this happens, all the bone spicules have been dissolved*
44
Q

how body reacts to accumulation of microcracks in bone matrix (bone fatigue) (which may lead to bone fracture)

A

sensed by osteocyte mechanosensory network.

-signals for bone remodelling to replace the microcracked bone

45
Q

what is the bone remodelling that we refer to when we say that osteocytes call for bone remodelling to repair microcracks (what is exactly happening)

A
  • Volkmann’s canals penetrate from periphery perpendicularly and then go up parallel to bone axis
  • form a big tunnel, hole.
  • interstitial systems (bad, old Hav systems)
  • then new addition and formation of bone
46
Q

first step when a bone is fractured

A
  • bone matrix is destroyed
  • bones adjoining the fracture die
  • damaged blood vessels produce a localized hemorrhage that forms a blood clot
47
Q

fracture repair: what happens to initial blood clot formed

A

removed during repair by macrophages

48
Q

steps of the repair of a fracture

A
  • periosteum and endosteum around the fracture proliferate
  • periosteum produces hyaline cartilage at the end of the fracture that is unstable
  • primary woven bone is formed by endochondral ossification
  • periosteum and endosteum produce more bone by intramembranous ossif
  • a CALLUS persists for some time
49
Q

fracture healing takes how long

A

1.5 months

50
Q

what happens during fracture repair between hyaline cartilage at end of fracture (unstable. produced by periosteum) and formation of primary woven bone

A
  • the chondrocytes in this hyaline cartilage receive no more blood bc no more blood vessels so they hypertrophy and die
  • ECM calcifies because of that*
  • osteoblasts come in and form woven bone
  • later bone replaced by compact bone (similar to fetal life bone replaced by lamellar bone)
51
Q

what happens to the bone callus with time

A

eventually is resorbed and you’re left with compact bone only

52
Q

what’s Wolff’s law

A
  • increased P on bone leads to bone resorption by osteoclasts
  • increase bone tension leads to bone formation by osteoblasts
53
Q

Wolff’s law is used where

A
  • orthodontics
  • distraction osteogenesis for bone lengthening
  • create tension to terminal part of dental arch and osteogenesis occurs on bone that is root of teeth*
54
Q

bone lengthening is done for who

A

children whose bones are skeletally immature (still growing**)

55
Q

what does distraction osteogenesis mean

A
  • bone cut during surgery and gradually distracted (pulled apart)
  • bone osteogenesis at site of lengthening occurs
  • break bone, attach pins to the bone, the pins pull the bone 1 mm every day
56
Q

bone regions involved in distraction osteogenesis

A
  • create a fracture = periosteum naturally responds by creating hyaline cartilage
  • the daily separation of the gap destroys the periosteum
  • periosteum produces more and more hyaline cartilage
  • hyaline cartilage eventually heals like in a fracture. (primary bone produced then replaced by secondary lamellar bone)
57
Q

other name of distraction osteogenesis

A

bone destruction

58
Q

bone struction most important conceps

A
  • create fracture
  • allows formation of cartilage
  • then pull on both ends
  • more cartilage added
  • cartilge replaced by woven bone
  • woven bone replaced by lamellar bone
59
Q

how does high Ca in the blood happen

A

bone resorption. a normal process in the bone, regulated by PTH indirectly

60
Q

PTH secreted by what + function

A
  • by parathyroid glands

- increase conc. of Ca in the blood

61
Q

PTH acts on what receptor and R is where

A

parathyroid hormone 1 receptor (PTH1R). most concentrated in

  • bone (on osteoblasts. NOT OSTEOCLASTS)
  • kidney
62
Q

what happens when PTH bind PTH1R on osteoblasts

A
  • stimulates osteoblasts to increase their expression of RANKL
  • inhibits osteoblast expression of OPG (osteoprotegerin)
63
Q

what does the reduced OPG expression by osteoblasts due to PTH help bone resorption

A
  • OPG binds RANKL normally and blocks it from interacting with RANK (the receptor for RANKL)
  • this usually stimulates osteoclasts precursors to fuse forming new osteoclasts which enhances bone resorption
64
Q

how does higher RANKL expression and lower OPG expression by osteoblasts due to PTH promote bone resorption

A
  1. more RANKL so more RANKL binding RANK to stim osteoclasts formation
  2. less OPG to block the RANKL-RANK interaction (by binding to RANKL) so more stimulation of osteoclast production can occur
65
Q

PTH is involved in the metabolism of what 2 things

A
  • calcium (Ca2+)

- phosphorus

66
Q

hormone that counteracts PTH

A

calcitonin

67
Q

calcitonin produced by what + its function

A
  • by parafollicular cells (C cells) of the thyroid gland

- lowers blood Ca

68
Q

4 ways by which calcitonin lowers blood Ca

A
  • inhibit Ca absorption by the intestines
  • inhibit renal tubular cell reabsorption of Ca so it is excreted in the urine
  • inhibits osteoclast activity in bones
  • stimulates osteoblast activity in bones
69
Q

calcitonin is especially useful at what times?

A
  1. during periods of calcium mobilization (bc it protects from ca loss from skeleton)
    - pregnancy
    - lactation
  2. prevents postprandial hypercalcemia resulting from absorption of Ca2+
70
Q

estrogen effect on bone + consequence of menopause

A

inhibits bone resorption

  • menopause = stop secreting estrogen so possibly more bone resorption
  • consider estrogen replacement therapy
71
Q

growth hormone (GH) secreted from where + effect

A
  • anterior lobe of pituitary gland

- makes liver produce somatomedin

72
Q

effect of somatomedin

A

overall growth effect on the epiphyseal plate + other structures of the bone

73
Q

consequence of lack of GH during the growing years

A

pituitary dwarfism

74
Q

consequence of excess of GH during the growing years

A

gigantism (excessive growth of long bones): excessive cartilage and bone formation at the epiphyseal plate of LONG bones

75
Q

consequence of excess of GH in the adult

A

acromegaly (increase in the width of bones due to periosteal growth)

76
Q

achondroplastic dwarfism is what

A

genetic defect caused a deficient or improper growth of the epiphyseal plate

77
Q

causes of pituitary dwarfism

A

anything that affects GH secretion

  • low GH
  • genetics
  • trauma to pituitary gland
  • surgical injury to pituitary
  • CNS trauma or tumor or radiation
  • often unknown*
78
Q

treatment of pituitary dwarfism

A

GH replacement therapy if child lacking GH

  • to be done before bone growth plates have fused or joined. once the growth plates have fused, GH replacement therapy is rarely effective
  • WINDOW OF THERAPY*
79
Q

achondroplasia vs pituitary dwarfism

A
  • pituitary dwarfism = proportions of the body reamin the same
  • achondroplastic dwarfism = proportions of the body are abnormal
80
Q

achondroplasia is what + meaning of the word

A

short limbed DWARFISM. achondroplasia means without cartilage formation
COMMON CAUSE OF DWARFISM

81
Q

cause of achondroplasia

A
  • gain of function (TM, transmembrane specifically in achondroplasia) mutation in fibroblast growth factor receptor 3 (FGFR3)
  • the protein is excessive
  • need 1 allele defect (autosomal dominant)
  • 2 bad alleles = lethal
82
Q

normal function of FGFR3

A

negative regulatory effect on bone growth during normal development of person or child

83
Q

what happens in mutated FGFR3 (transmembrane mutation)

A
  • mutated form of R is constitutively active

- severely shortened bones

84
Q

exact function of FGFR3 on cell signaling and bone ossification specifically

A
  • represses the number of chondrocytes that proliferate and mature into bone at the growth plate
  • gain of function and ossification is repressed even more
  • epiphyseal plate is disorganized, with a much smaller cartilage
  • gain of function = it accomplishes its function of repression cartilage maturation into bone too much*
85
Q

long bones growth takes how long in humans + regulated by what hormone

A
  • 20 years

- GH

86
Q

does the thickness of the epiphyseal plate change with time

A
  • no. because rate of chondrocyte prolif and bone formation = rate of destruction of spicules
  • the epiphyseal plate is simply displaced away from the middle of the diaphysis with time (resulting in net growth in length)

Bloc H - Movement (48 decks)

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