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LOCO2 > Bone Metabolism > Flashcards

Bone Metabolism Flashcards

1
Q

What are bone lamellae?

A

Bone layers

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2
Q

What are the 2 types of bone and that is their proportion?

A
  • cortical/compact (80%)

- cancellous/trabecular/spongy (20%)

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3
Q

What are the properties of compact/cortical bone?

A
  • found on edges of bone
  • compressive strength
  • from osteons laying on top of each other in circular pattern
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4
Q

What are the properties of cancellous bone?

A
  • inside diaphysis and heads of bone
  • mesh like
  • relatively strong but bendable for movement
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5
Q

What is the medullary cavity?

A
  • sits inside shaft
  • bone marrow
  • lightens skeleton and houses haematopoietic cells
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6
Q

What is bone marrow like at birth?

A
  • virtually all bone marrow is red bone marrow

- yellow bone marrow forms peripherally and moves towards central axial skeleton

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7
Q

What is bone marrow like in adults?

A
  • little red bone marrow as don’t need many haematopoietic stem cells
  • found in spongy bones of vertebrae, ribs, sternum, cranium and epiphyses of long bones
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8
Q

What is woven bone?

A
  • less resistant to stress
  • can be put down quickly
  • more disorganised vs. lamellar
  • random collagen I organisation
  • immature/mechanically weak, healing
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9
Q

What are the 2 categories of bone composition?

A
  • organic (35-40%)

- inorganic (60%)

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10
Q

What are the components of organic bone material?

A
  • collagen type 1
  • proteoglycans
  • growth factors/cytokines/osteoid
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11
Q

What are the features of collagen type I?

A
  • 90% tensile strength

- rope-like collagen forming long fibres

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12
Q

What are the features of proteoglycans?

A
  • compressive strength as hold water
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13
Q

What produces organic bone material?

A
  • cells = osteoblasts, osteocytes, osteoclasts
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14
Q

What is the main inorganic bone component?

A
  • calcium hydroxyapatite
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15
Q

What are the features of calcium hydroxyapatite?

A
  • precipitates onto surface of collagen fibres
  • doesn’t cover it properly otherwise bone would be brittle and unbendable
  • forms intermittent crystal precipitate leaving little gaps at regular intervals allowing bendability
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16
Q

Why is bone not picked up on an MRI?

A
  • quite dry -> 5% water
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17
Q

What are the main cells found in bone?

A
  • osteoprogenitor cells
  • osteoblasts
  • osteocytes
  • osteoclasts
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18
Q

What are the features of osteoprogenitor cells?

A
  • CT cells
  • from mesenchyme during embryonic development
  • sits on either side of periosteum and become osteoblasts if needed
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19
Q

What are the features of osteoblasts?

A
  • secrete mineralised organic component

- become surrounded by it to become an osteocyte

20
Q

What are the features of osteocytes?

A
  • remain in bone structure and secrete collagen locally
  • have canaliculi
  • death signals remodelling
21
Q

What are canaliculi?

A
  • processes from osteocytes
  • go into canals through bone matrix
  • sense how much bone is bending/compressing/crushed
  • to sense if new bone is required
22
Q

What are the features of osteoclasts?

A
  • from haematopoietic stem cells within bone marrow

- macrophage like cells

23
Q

What are haversian canals?

A
  • contain blood vessels
24
Q

Why does bone remodelling occur?

A
  • renews bone deterioration

- redistribution of bone matrix along mechanical stress lines

25
Q

What is sclerostin?

A
  • glycoprotein
  • secreted by osteocytes when healthy
  • inhibits osteoblasts
  • switched off when osteocyte dies stimulating bone growth
26
Q

How do osteoclasts and osteoblasts signal?

A
  • bidirectional communication

- via ligands and receptors to inhibit osteoclasts increasing bone production

27
Q

What is the function of EphrinB2?

A
  • ligand

- on surface of osteoclasts

28
Q

What is the function of EphB4?

A
  • receptor

- expressed by osteoblasts

29
Q

What increases ephrinB2 expression?

A

PTH

30
Q

What is the difference between trabecular and cortical bone?

A
  • trabecular bone 3-10 times quicker than cortical bone as larger SA and responds to stresses on bone quicker
31
Q

What do osteoclasts do in bone production?

A
  • signalled by osteocytes (amoeboid movement)
  • attach to area and form leak proof seal
  • inferior ruffled border secretes vesicle with HCl and protein digesting enzymes
  • HCl dissolves calcium hydroxyapatite and bone mineral part
  • protein digesting enzymes break down collagen
  • end up with mixture of digested collagen, calcium and phosphate salt taken up by osteoclast
  • packed into a vesicle and transported across cytoplasm
  • release calcium salts into interstitial fluid
32
Q

What do osteoblasts do in bone production?

A
  • move in and secrete new osteoid which is at first not mineralised
  • osteoid mineralised 1 week later
33
Q

How is bone remodelling done using tetracycline?

A
  • antibiotic taken up by mineralising bone and fluoresces
  • check if bone being mineralised
  • 2 doses 14 days apart (2 lines indicate mineralisation)
34
Q

Where is calcium in bone?

A
  • 99% in skeleton

- 1% in cells/blood/body fluids

35
Q

What is the function of calcium in bone metabolism?

A
  • signalling molecule

- regulates muscle contraction, neuronal signalling, heart beats

36
Q

What does maintenance of calcium depend on?

A
  • intestinal absorption
  • renal absorption
  • skeletal mobilisation
37
Q

What is the function of phosphate in bone production?

A
  • contain in hydroxyapatite
  • uses PTH to modulate absorption and excretion
  • not as closely regulated as calcium
38
Q

How is calcium regulated?

A
  • low plasma Ca2+ = PTH secretion from parathyroid gland on back of neck
  • high plasma Ca2+ = calcitonin release
39
Q

What does PTH promote?

A
  • immediately Ca2+ reabsorption from kidney and PO4- excretion
  • LT Ca2+ reabsorption from bone increases number and activity of osteoclasts
40
Q

What does osteoclast formation require?

A
  • RANKL
  • M-CSF
    (produced by osteoblasts and stromal cells)
41
Q

What is RANK-L?

A
  • osteoblasts have receptor for PTH
  • stimulate osteoblasts to produce RANKL -> RANK (receptor) stimulated on osteoclasts
  • causes osteoclast precursor to proliferate and differentiate
42
Q

What inducers RANK-L?

A
  • vitamin D
43
Q

What inhibits RANK-L?

A
  • estrogen
44
Q

What is M-CSF?

A

Macrophage colony-stimulating factor

45
Q

What is OPG?

A
  • decoy receptor for RANKL
  • modulates signalling on RANK by soaking up RANKL to stop signalling to osteoclast precursor
  • induces synthesis of active vitamin D increases calcium absorption from gut
46
Q

What is the effect of calcitonin?

A
  • released when high calcium
  • inhibits osteoclast differentiation and activity
  • increases calcium excretion from kidney
  • inhibits calcium absorption from intestines

LOCO2 (26 decks)

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