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Locomotor > Bone Metabolism & Remodelling > Flashcards

Bone Metabolism & Remodelling Flashcards

1
Q

when does bone development start (at how many weeks) during gestation? [1]

what are the two ways can develop bone? [2]

A

when does bone development start (at how many weeks) during gestation? [1]
6-7 weeks

what are the two ways can develop bone? [2]

  • *intramembranous ossification:** direct bone formation, many skull bones
  • *endochondral ossification:** most of skeleton, cartilage first & then bone
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2
Q

intramembranous ossifcation: describe direction of bone growth

A

bones develop at centres of ossification and grow outwards - connecting to neighbouring bone at cranial suture

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3
Q

how does endochondral ossification occur?

A

- Mesenchymal cells condense and differentiates into chondroblasts to produce hyaline cartilage model extracellular matrix (so they use collagen type 2 rather than collagen type 1).

  • the perichondrium forms around cartilage model and holds all the mesenchymal cells next to the condensing bone
  • To begin with, ECM is made more from collagen type 2, more proteoglycans: causes cartilage to grow in legnth and width (into the shape of the bone): causes to be further away from nutrient source
  • chondrocytes now in the middle will begin to deteriorate as there is no blood supply into this cartilage
  • this creates cavities, right in the centre, where the cartilage used to be. When they die, this triggers calcification as it triggers a Ph change: It releases vesicles in the chondrocytes with enzyme like alkaline phosphatase which changes the ph and encourages calcification of the matrix.

At this time, a blood vessel known as the nutrient artery can penetrate the perichondrium and begin to bring in osteoclasts from the haemopoietic cells to start remodelling: break down some of the spongy bone to create a marrow, or medullary, cavity in the centre.

Bone on the inside and bone on the outside grow towards each other to completely replace the cartilage.

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4
Q

where do you find epiphyseal growth plates in bone [2]?

what goes on at epiphyseal growth plates?

A

where do you find epiphyseal growth plates in bone [2]?

  • minumun of 2: medial and distal end of bones (sometimes more)
  • hyaline cartilage between epiphysis and diaphysis

what goes on at epiphyseal growth plates?
- hyaline cartliage replaced by bone to cause increase in bone lenght

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5
Q

which is your last bone to ossify? [1]

A

clavicle

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6
Q

what happens to bone in the middle, as it develops from child to adult? why?

what is name for what is left in the middle?

A

infant / child bone increases in width BUT at the same time, bone is lost in the centre via osteoclasts

otherwise would be too heavy / brittle

in centre = intra medullary cavity

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7
Q

what is cortical (compact) vs cancellous (trabecular / spongy bone)

A
  • *cancellous (trabecular / spongy bone)**
  • 20 % of mass BUT 80% of surface area
  • 5-7% density of cortical bone
  • trabecuale - plates and rods
  • home for bone marrow
  • *cortical bone (compact)**
  • epiphysis - thin shell
  • diaphysis - thicker layer to give support to outer edge of bone
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8
Q
A
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9
Q

what are the different types of bone marrow/ [2]

how does bone marrow change throughout lifetime? (infant –> adult)?

A

what are the different types of bone marrow? [2]

  • **yellow - more adipocytes
  • red - more haemopoetic cells**

how does bone marrow change throughout lifetime? (infant –> adult)?

  • newborn - nearlly all red bone marrow
  • adult - more yellow
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10
Q

when do you find woven bone in the body? [2]

what does it look like? [1]

A

when do you find woven bone in the body? [2]

  • **immature childhood bone
  • healing of fractures**

what does it look like? [1]
- lamella (layers of bones) not in orders

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11
Q

what is yellow and red?

A

red - lamellar bone
yellow - woven bone

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12
Q

what is the name of the inorganic substance that is precipitated over collagen fibres to calcify it? [1]

what is structure of ^ like on collagen fibres? [1]

A

what is the name of the inorganic substance that is precipitated over collagen fibres to calcify it? [1]
95% calcium hydroxyapatite

what is structure of ^ like on collagen fibres? [1]
- as crystals

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13
Q

which cells make bone ECM (type 1 collage / proteoglycans)? [1]

which cells are maintainers of bone? [1]

A

which cells make bone ECM (type 1 collage / proteoglycans)? [1]
osteoblasts

which cells are maintainers of bone? [1]
osteocytes

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14
Q

what substance is secreted that makes osteoclasts differentiate into osteoclasts? [1]

A

what substance is secreted that makes osteoclasts differentiate into osteoclasts? [1]
RANKL

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15
Q

where do you find osteoprogenitor (bone stem cell) [2]

what is fate of osteoblasts? [2]

A

where do you find osteoprogenitor (bone stem cell) [2]

  • *- periosteum
  • endosteum**

what is fate of osteoblasts? [2] become either:

  • *- osteocyte
  • lining cell:old osteoblast that arenot encased in own matrix** to help regulate calcium entry into and out of bone. can be reactivated by PTH
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16
Q

why does bone need to remodel? [2]

which part of bone has most bone remodelling? [1] why [2]

A

why does bone need to remodel? [2]

  • -***before deterioration
  • **along lines of mechanical stress

which part of bone has most bone remodelling? [1] why [2]

  • trabecular bone: 3x10 more quicker than cortical
  • *- larger sa
  • responds to stress quicker**
17
Q

what are the internal [1] and external signals [2] for bone remodelling?

A

what are the internal and external signals for bone remodelling?

  • *internal factors**
  • osteocytes processes extend in canaliculi & touch their neighbours
  • osteocytes produce sclerostin to indicate bone health ! - stops osteoblasts coming
  • when osteocytes stop producing sclerostin: indicates bad bone health
  • *external factors**
  • serum calcium level: low serum calcium causes the release of parathyroid hormone - causes osteoblasts to make RANK L
  • pro-inflam cytokines: IL1, IL6, IL17 & TNF
18
Q

what do osteoclasts look like? [1]

explain mechanism of bone remodelling occurs xox

A

osteoclasts - multinucleated macrophage relation

  • look for areas of bone that need to be renewed
  • make leak proof seal over the area
  • secrete enzymes & HCl that will dissolve the calcium hydroxyapatite
  • osteoclasts take up calcium & proteins pump into interstitial fluid
  • osteoclasts find new area
  • osteoblasts come in & fill lacuna with osteoid - firstly NOT MINERALISED
  • *-** approx 7-10 days osteoid is mineralised
  • osteoblast becomes encased & beomes osteocyte
19
Q

where do we get most of calcium from for bone?

how do we maintain normal serum calcium levels? [3]

A

normal diet means we don’t need to use calcium stores in bone

how do we maintain normal serum calcium levels? [3]

  • **intestinal absorb
  • renal excretion
  • skeletal mobilistain**
20
Q

what is the effect of when low Ca2+ serum causes PTH to be secreted in? [3]

A
  • low serum Ca2+ (below 2.2 mmol/L) stimulates parathyroid hormone (PTH) secretion
  • PTH promotes
    i) Ca2+ reabsorbtion from kindey and PO4 excretion
    ii) @ kindey: synthesis of 1,25 dihydroxyvitamin D -> i_ncreases calcium absorbtion from gut_
    iii) **Ca2+ reabsorbtion from bones - increases activity and no. osteoclasts
  • **PTH binds to osteoblasts; osteoblasts produce RANKL; osteoclasts have RANKL receptor; activates osteoclasts
21
Q

how does PTH cause Ca2+ reabsorbtion from bones via the increase of activity and no. osteoclasts? [3]

A

Ca2+ reabsorbtion from bones - increases activity and no. osteoclasts
PTH binds to osteoblasts
osteoblasts produce RANKL
osteoclasts have RANKL receptor
activates osteoclasts

22
Q

when Ca2+ levels are back to normal, how do we stop things that occured when it was low? [3]

A
  • stop production of PTH
  • calcitonin: released from C cells in thyroid gland
    i) inactivates osteoclasts
    ii) increases Ca2+ bones can accept
    iii) increases renal Ca2+ reabsorb
23
Q

which two other hormones influence Ca2+ absorption?

A
  • *oestrogen**
  • increases Ca2+ in gut
  • bone decreased reabsorb

glucocorticoid

Locomotor (30 decks)

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