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Locomotor > :D > Flashcards

:D Flashcards

1
Q

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

A
  • *intramembranous ossification**: direct bone formation, many skull bones
  • *endochondral** ossification: most of skeleton, cartilage first & then bone
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2
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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3
Q

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

A

RANKL

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4
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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5
Q

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

A
  • osteocyte
  • lining cell: old osteoblast that are not encased in own matrix to help regulate calcium entry into and out of bone. can be reactivated by PTH
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6
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
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7
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
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8
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
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9
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
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10
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

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11
Q

how does body stop cell from producing more Ca2+?

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
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12
Q

explain how intramembranous ossificatin occurs xo

A
  • ossification centre appears in fibrous connective tissue membrane: here mesenchymal cells condense and differentiate as osteogenic cells: osteoblasts
  • Osteoblasts secrete bone matrix (osteoid) & matrix becomes calcified with calcium hydroxyapatite
  • trapped osteoblasts become osteocytes
  • Mesenchyme on outside condenses: periosteum
  • blood vessels growing to supply the bone with nutrients will bring in osteoclasts, which can then remodel the bone into compact/cortical bone on the outside and trabecular bone on the inside.
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13
Q

what are 5 stages of epiphyseal growth plate?

A
  • Zone of resting cartilage
  • Zone of proliferating cartilage
  • Zone of hypertrophic cartilage
  • Zone of provisional calcifcation
  • zone of ossification
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14
Q

how does appositional growth of bone occur? (to the side)

A
  • osteoprogenitors in periosteum differentiate as osteoblasts – secrete new bone matrix to form compact, cortical bone (osteons) and grow on either side of a blood vessel.
  • these ridges get bigger and eventually form a tunnel with a blood vessel right in the centre.
  • Inside tunnel: Former periosteum becomes endosteum due to being enclosed inside the bone due to bone growth. It still has progenitor cells
  • Osteoblasts make new bone lamellae filling tunnel
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15
Q

how does appositional growth of bone occur? (to the side)

A
  • osteoprogenitors in periosteum differentiate as osteoblasts – secrete new bone matrix to form compact, cortical bone (osteons) and grow on either side of a blood vessel.
  • these ridges get bigger and eventually form a tunnel with a blood vessel right in the centre.
  • Inside tunnel: Former periosteum becomes endosteum due to being enclosed inside the bone due to bone growth. It still has progenitor cells
  • Osteoblasts make new bone lamellae filling tunnel
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17
Q

in appositional growth, why is bone must be removed from the inner medullary cavity?

A
  • As new bone added to outside of bone, bone must be removed from the inner medullary cavity so that we maintain the same proportions of cortical:trabecular bone
  • Addition of new bone needs to be matched with removal to maintain the thickness
18
Q

give two reasons why skeleton is renewed before it deteriotes [2]

which type of bone is quicker at remodelling? [1]

A

give two reasons why skeleton is renewed before it deteriotes [2]

  1. renews bone before deterioration
  2. redistributes bone matrix along lines of mechanical stress

which type of bone is quicker at remodelling? [1]

Trabecular bone 3-10 times quicker than cortical bone: Larger surface area, Responds to stresses on the bone quicker

19
Q

which cell signals bone remodelling? [1]

what hormone does ^ cell secrete? [1]

how does the process occur? [2] (basic)

A

which cell signals bone remodelling? [1]
-osteocytes

what hormone does ^ cell secrete? [1]
sclerostin

how does the process occur? [2]

  • *-sclerostin** secreted: causes inhibition of osteoblast action
  • cellular process extend in canaliculi and touch their neighbours
20
Q

explain mechanism of how osteoclasts resorb bone?

A
  • osteoclasts clamps down onto surface of the bone and forms a leak proof seal [1]
  • Release protein-digesting enzymes, and acid (HCL) underneath: this breaks down and digest collagen fibres
  • low pH of 5 dissolves the bone minerals
  • bone proteins and minerals (mainly Ca2+) cross osteoclast to exit into interstitial fluid so these can be re-used
  • once the osteoclasts have moved to the next area to remodel new bone, the area gets covered with osteoblasts: fill lacuna with osteoid (collagen type 1 and proteoglycan). This is UNMINERALISED BONE MATRIX
  • takes about 7-10 days for the calcium to be precipitated over the new bone & osteon is reminarlised
21
Q

explain mechansim of bone metabolsim through PTH secretion

A
  • Low plasma Ca2+ stimulates Parathyroid hormone (PTH) secretion: Parathyroid glands
  • Ca2+ reabsorption from kidney and PO4 excretion (at the expense of phosphate as we can make this easily)
  • Initiates synthesis of 1,25-dihydroxyvitamin D (1,25 (OH)2 vitamin D3) in kidney, as 1,25 (OH)2 vitamin D3 increases Ca2+ absorption from gut
  • Ca2+ reabsorption from bone - increases number and activity of osteoclasts
  • Osteoblasts have receptor for PTH - causes expression of RANKL (ligand for RANK)
  • Osteoclast precursors have RANK (receptor)
  • If osteoblasts produce RANKL it stimulates osteoclasts to produce more, thus mobilising calcium in your skeleton
  • RANKL/RANK = Osteoclast proliferation and differentiation
22
Q

explain mechansim of bone metabolsim through PTH secretion

A
  • Low plasma Ca2+ stimulates Parathyroid hormone (PTH) secretion: Parathyroid glands
  • Ca2+ reabsorption from kidney and PO4 excretion (at the expense of phosphate as we can make this easily)
  • Initiates synthesis of 1,25-dihydroxyvitamin D (1,25 (OH)2 vitamin D3) in kidney, as 1,25 (OH)2 vitamin D3 increases Ca2+ absorption from gut
  • Ca2+ reabsorption from bone - increases number and activity of osteoclasts
  • Osteoblasts have receptor for PTH - causes expression of RANKL (ligand for RANK)
  • Osteoclast precursors have RANK (receptor)
  • If osteoblasts produce RANKL it stimulates osteoclasts to produce more, thus mobilising calcium in your skeleton
  • RANKL/RANK = Osteoclast proliferation and differentiation
23
Q

explain mechanism of how osteoclasts resorb bone?

A
  • osteoclasts clamps down onto surface of the bone and forms a leak proof seal [1]
  • Release protein-digesting enzymes, and acid (HCL) underneath: this breaks down and digest collagen fibres
  • low pH of 5 dissolves the bone minerals
  • bone proteins and minerals (mainly Ca2+) cross osteoclast to exit into interstitial fluid so these can be re-used
  • once the osteoclasts have moved to the next area to remodel new bone, the area gets covered with osteoblasts: fill lacuna with osteoid (collagen type 1 and proteoglycan). This is UNMINERALISED BONE MATRIX
  • takes about 7-10 days for the calcium to be precipitated over the new bone & osteon is reminarlised
24
Q

which cell signals bone remodelling? [1]

what hormone does ^ cell secrete? [1]

how does the process occur? [2] (basic)

A

which cell signals bone remodelling? [1]
-osteocytes

what hormone does ^ cell secrete? [1]
sclerostin

how does the process occur? [2]

  • *-sclerostin** secreted: causes inhibition of osteoblast action
  • cellular process extend in canaliculi and touch their neighbours
25
Q

give two reasons why skeleton is renewed before it deteriotes [2]

which type of bone is quicker at remodelling? [1]

A

give two reasons why skeleton is renewed before it deteriotes [2]

  1. renews bone before deterioration
  2. redistributes bone matrix along lines of mechanical stress

which type of bone is quicker at remodelling? [1]

Trabecular bone 3-10 times quicker than cortical bone: Larger surface area, Responds to stresses on the bone quicker

26
Q

in appositional growth, why is bone must be removed from the inner medullary cavity?

A
  • As new bone added to outside of bone, bone must be removed from the inner medullary cavity so that we maintain the same proportions of cortical:trabecular bone
  • Addition of new bone needs to be matched with removal to maintain the thickness
27
Q

?

A

rhomboids

28
Q
A
29
Q
A

supinator

30
Q
A

dorsal interossei of hand

dorsal interrossei: abduct fingers (DAB)​

Locomotor (30 decks)

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