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Medicine yr1 > MSK-bone biology > Flashcards

MSK-bone biology Flashcards

1
Q

what is bone?

A

connective tissue consisting of a soft porous network (trabeculae) surrounded by a harder dense exterior (cortex)

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2
Q

what are the functions of bone (4)?

A
  • Supports soft tissue and provides attachment site for skeletal muscles to aid movement
  • Protects internal organs
  • Site of Haematopoiesis
  • Regulates Mineral Homeostasis – store of Ca2+
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3
Q

what is the diaphysis of the bone?

A

the long, cylindrical, main portion of the bone.

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4
Q

what is the epiphyses of the bone?

A

the proximal and distal end of bone

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5
Q

what are the metaphyses of the bone?

A

regions between the diaphysis and the epiphyses

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6
Q

what is the medullary cavity of the bone made up of ?

A
  • hollow, cylindrical space within diaphysis containing:
  • —>red marrow
  • —>yellow marrow (adipose tissue)
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7
Q

what does compact bone form?

A

the hard exterior of bone, consisting of dense tissue with few spaces

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8
Q

what are osteons?

A
  • the repeating structural units of compact bone

- each consists of concentric rings of hard, calcified extracellular matrix-lamellae

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9
Q

what does the lamellae surround?

A

-a small network of blood vessels and nerves located in a central canal (Haversian)

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10
Q

how are osteons in compact bone aligned to resist fracturing?

A

in the same direction, parallel to the length of the diaphysis, providing resistance to bending/fracturing

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11
Q

what are the volksmann’s canals?

A

exist perpendicular to the Haversian canal and connect the periosteum to the interior of the bone

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12
Q

what is trabecular bone?

A

Spongy interior of bone, consisting of a network of lamellae arranged in fine, irregular columns - Trabeculae.

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13
Q

how are trabeculae separated and how does this help with its function?

A
  • separated by spaces, filled with bone marrow and are orientated along lines of stress
  • allowing t bone to be lightweight-move more readily when pulled by skeletal muscle
  • stress resistant to protect bone marrow
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14
Q

what is the periosteum?

A

the tough connective tissue sheath (and its associated blood supply) that surrounds the bone surface (wherever it is not covered by articular cartilage)

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15
Q

what is the periosteum composed of?

A
  • an outer fibrous layer of dense irregular connective tissue
  • an inner osteogenic layer that consists of cells
  • has a rich blood supply and high volume of vasomotor and sensory nerves in order to respond with high sensitivity to injury
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16
Q

what is the endosteum composed of?

A
  • layer of connective tissue that lines the inner surface of bone
  • consists of osteoprogenitor cells and loose connective tissue perforated by blood vessels
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17
Q

name the 4 different bone cells.

A
  • osteoprogenitor cell
  • osteoblast
  • osteocytes
  • osteoclasts
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18
Q

what are osteoprogenitor cells?

A

pre-cursors of osteoblasts derived from mesenchymal bone cells

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19
Q

where are osteoprogenitor cells found?

A
  • along the inner portion of the periosteum
  • in the endosteum
  • in canals
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20
Q

what are the roles of osteoblasts?

A
  • bone forming cells of mesenchymal origin
  • expressing ALP (alkaline phosphatase)
  • synthesise and secreted unmineralised bone matrix in response to cytokines/ growth factors
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21
Q

what are osteocytes?

A

matured osteoblasts embedded in mineralised bone matrix

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22
Q

what is are the roles of osteocytes?

A
  • maintain bone tissue in response to mechanical loading

- produce factors that regulate bone cells

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23
Q

which factors regulate bone cells?

A
  • prostaglandins
  • RANKL
  • sclerostin
24
Q

what type of cells are osteoclasts?

A

-motile, multinucleate cells

25
Q

what is the role of osteoclasts?

A

bone resorbing cell

26
Q

how does the structure of osteoclasts help with bone resorption?

A

-osteoclasts plasma membrane is deeply folded into a ruffled border (layer facing bone surface)-produce lysosomal enzymes and acids to catabolise protein and mineral components of ECM

27
Q

what is bone remodelling useful for?

A
  • used to maintain and grow the skeleton (renewal every 7-10 years)
  • respond to altered mechanical requirements (Wolff’s law)
  • repair damage (micro/macro features)
  • response to calcium deficit
28
Q

what is ALP?

A

alkaline phosphatase

29
Q

what are the local factors involved the bone metabolism?

A
  • prostaglandins

- cytokines

30
Q

how do prostaglandins regulate bone metabolism?

A

-fatty acid metabolites (produced by osteoblasts) increase and decrease osteoclast activity to mediate the actions of growth factors and responses to mechanical loading

31
Q

how do cytokines regulate bone metabolism?

A
  • produced by immune cells and bone cells increase osteoclast recruitment and activity, increasing bone loss.
  • sex steroids can inhibit interleukin activity
32
Q

what does the bone matrix consist of?

A

-Inorganic Hydroxyapatite Mineral = Calcium Phosphate Salt crystals surrounding collagen fibres to provide rigidity and strength

-Organic Osteoid = 90% type I collagen - (Structural protein providing strength, flexibility)
& 10% Mixture - Growth factors- Osteocalcin (bone formation marker)/ Osteonectin Osteopontin/ Glycoproteins

33
Q

what is mineralisation of osteoid promoted by?

A

hormonally active vitamin D3

34
Q

what 2 bone types does mineralisation of osteoid by vitamin D3 produce?

A
  • woven bone

- lamellar bone

35
Q

what is woven bone?

A

an immature form of bone

36
Q

describe how woven bone is produced.

A

produced when osteoblasts secrete osteoid rapidly eg in foetal bone development/ fracture repair in adults

37
Q

what does rapidly formed woven bone eventually from?

A

remodelled to form lamellar bone in adults-stronger and more resilient

38
Q

what is lamellar bone comprised of ?

A

regular parallel band of collagen arranged in sheets

39
Q

describe how bone resorption occurs.

A
  • Osteoclasts attaches to the bone surface at the endosteum/periosteum and form a leak proof seal at the edges of its ruffled border
  • RANKL stimulates osteoclast formation and activity
  • osteoclast now release protein-digesting lysosomal enzymes and acids into the sealed pocket
  • the enzymes digest collagen fibres while acids dissolve the bone minerals
  • degraded bone proteins and extracellular matrix minerals (Ca2+ and PO4-) enter an osteoclast by endocytosis, cross the cell vesicles and are exocytosed on the opposite membrane of ruffled border into interstitial fluid
  • then diffused into nearby blood capillaries
40
Q

how are bones reformed?

A
  • small area of bone has been resorbed
  • osteoclasts depart
  • osteoblasts move in expressing ALP and secreting unmineralised bone matrix
41
Q

what is the main role of vitamin D?

A

to maintain Ca2+ and PO4- at optimum serum/ blood levels by helping them be absorbed in the gut

42
Q

what are adequate levels of Ca2+ and PO4- required for?

A
  • promoting mineralisation of the osteoid ECM of bone

- functioning of skeletal muscle

43
Q

how is active vitamin D made?

A

1- 7-dehydrocholesterol (vit D3) is found in the skin or taken in from the diet
2-it absorbs UVB to form pre-vit D
3-heat causes pre-vit D to form vit D-transported to liver
4-in the liver 25(OH)ase converts Vit D to 25(OH)D
5-in the kidney 1-alpha-(oh)ase converts 25(OH) 1,25 (OH)2D—>this is active form of vit D

44
Q

what are the direct effects of activated vitamin D?

A

-increase Ca2+ absorption in the gut (by inducing Ca2+ binding protein expression)
-decrease synthesis of PTH (as PTH also increases Ca2+ so not needed)
-inhibits action of 1-alpha(OH)ase in the kidney (with neg feedback loop)
-increases bone resorption (by increasing RANK-L expression-increases osteoclast activity)
(OVERALL EFFECT:all increase levels of serum & blood Ca2+/PO4-)

45
Q

what are the indirect effects of activated vitamin D?

A

increases bone mineralisation using Ca2+ and PO4-
-increase serum ca/po by stimulating osteoclast activity-so osteoblasts can reform bone with high conc of minerals required fro bone deposition

(OVERALL EFFECT: remodelling bone)

46
Q

what are the causes of vitamin D deficiency?

A
  • reduced skin synthesis
  • increased melanin (which absorbs UVB)
  • decreased bioavailability (due to malabsorption of fat in gut)
  • decreased synthesis of 25(OH)D-liver failure
  • decreased synthesis of 1,25(OH)2D-kidney disease
47
Q

what are the clinical consequences of vitamin deficiency?

A
  • muscle weakness
  • osteoporosis
  • rickets (children)-bone softening
  • osteomalacia (adults)-bone softening
48
Q

how does vit D deficiency lead to osteoporosis?

A

weakness of bone due to lack of balance between bone reabsorption and deposition

49
Q 
the inner lining of bone shaft is called?
A-osteon
B-periosteum
C-endosteum 
D-osteoblast
A

C

50
Q 
long bones enlarge at the ends into:
A-osteons 
B-periosteum
C-endosteum
D-epiphysis
A

D

51
Q 
compact bone is made up of:
A-osteons
B-trabeculae spicules
C-spongy bone
D-all of above
A

A

52
Q 
Bones serve all of the following functions except:
A-support/ protection/ movement 
B-transportation of substances 
C-storage 
D-blood cell formation
A

B

53
Q

where are osteoclasts concentrated?

A

endosteum

54
Q

where are osteoclasts derived from?

A

fusion of monocytes

55
Q

how are the collagen fibres arranged in woven bone?

A

randomly arranged collagen fibres in the osteoid

56
Q

how are lamellae arranged in trabecular bone?

A

in a network arranged in fine irregular columns—>Trabeculae

Medicine yr1 (55 decks)

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