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Medsci 142 > Musculoskeletal > Flashcards

Musculoskeletal Flashcards

1
Q

choose the option that is correct:
Osteoclasts:

-are found in the resting endosteum and periosteum

-secrete their enzymes into an acidic environment in order to activate them

-are less common on trabeculae due to the reduced surface area

-remove hydroxyapatite by secreting enzymes

-use the clear zone to keep the destructive elements that they secret out of their Howship’s lacunae

A

secrete their enzymes into an acidic environment in order to activate them

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2
Q

where are most long bones found?

A

Appendicular skeletone

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3
Q

what are the functions of the appendicular skeleton?

A

-movement
- fat storage(yellow)

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4
Q

how many bones are there in the axial skeleton?

A

80( some paired)

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5
Q

how many bones are there in the appendicular skeleton?

A

126(paired)

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6
Q

what are the functions of the axial skeleton?

A

support/protection
Haemopoises( red bone marrow)

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7
Q

what is the bone marrow at birth?

A

ALL red

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8
Q

how is bone count reduced throughout a lifetime?

A

during puberty, some bones fuse
elderly- even more bones fuse

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9
Q

what is the organization of a long bone?

A
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10
Q

width of the compact bone in epiphysis compared to the diaphysis

A

compact bone is thinner
in epiphysis( ~ 1 mm)

compression force between 2 bones allows a thin layer of compact bone if supported by trabecular from below

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11
Q

is there periosteum in the epiphysis?

A

No as in contact with another bone

instead have a tougher layer of articulate cartilage

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12
Q

what are the forces acting on the epiphysis of the fema?

A

compression and tension

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13
Q

where is endosteum found in the spongy bone?

A

covers the trabeculae

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14
Q

organisation of epiphysis

A

more spongy bone

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15
Q

organisation of diaphysis

A

cylinder shape, hollow( medullary cavity with bone marrow). Lightweight

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16
Q

what is the function of perforating (Sharpey’s) fibers

A

forms strong unions between structures outside the bone to the bone

Big where tendons and ligaments attach to the bone

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17
Q

what is the size of the compact/cortical bone in the diaphysis?

A

~1 cm
thick to withstand parallel forces

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18
Q

what types of fibers are in the bone ECM?

A

collagen fibres type 1 and 5

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19
Q

what types of fibers are in the bone ECM?

A

collagen fibers type 1 and 5

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20
Q

what is the function of collagen fibers in bone?

A

resist tension( stretching/pulling)

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21
Q

what does the ground substance in the bone contain?

A

hydroxyapatite

Ca10(PO4)6OH2

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22
Q

what is the function of the ground substance in bone?

A

resists compression (squeezing/crushing)

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23
Q

what type of cells are in the bone?

A

osteogenic
osteoblast
osteocyte
osteoclasts

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24
Q

overall what force does the bone resists?

A

tension+ compression= torsion

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25
Q

where are osteogenic cells located?

A

the surface of the bone in the periosteum and endosteum. Also inside central canals of compact bone

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26
Q

the function of osteogenic cells

A

normally dormant, but can divide and supply developing bine with bone-forming cells

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27
Q

the function of osteogenic cells

A

normally dormant, but can divide and supply developing bine with bone-forming cells

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28
Q

where are osteoblasts located?

A

usually in the layer under the peri or endosteum, wherever new bone is being formed

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29
Q

function of osteoblasts

A

synthesis, deposition and calcification of osteoid

put down new bone

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30
Q

when is the layer active?

A

when osteoblasts are present

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31
Q

what is osteoid?

A
  • The organic extracellular matrix (mainly collagen) of bone, synthesized by osteoblasts prior to mineral deposition.
  • Osteoid is 70% collagen with the remainder consisting of proteoglycans, other proteins and water.
32
Q

what is calcification?

A
  • This precursor matrix(osteoid) is eventually infiltrated with bone salts (hydroxyapatite) and this process is called calcification.
  • This makes the bone strong but also dense, thus nutritive fluids cannot diffuse freely through it
33
Q

how rapid is calcification?

A

can calcify an osteoid 70-80% in the 1st 3 weeks

after the initial 3 weeks can take years to fully calcify the bone

34
Q

what is osteocyte and where is it located?

A

An osteoblast trapped within
lacunae inside the bone.
Osteocytes can
communicate with
neighboring cells
through their long
cellular processes
inside canaliculi

35
Q

function of osteocytes

A

Bone tissue
maintenance
- live lattice inside the bone.
- localized minor repair
- Rapid Ca exchange

36
Q

osteoclast

A

Fusion of
monocyte
(White Blood Cell)
progenitor
cells.

37
Q

osteoclast function

A

Secretes acid and
enzymes.
Dissolves the
mineral and organic
components of
bone.

38
Q

how long do osteoclasts live for?

A

2-3 months before self-destruction

39
Q

what are the steps in osteoclast function?

A

1st: Dissolve
2nd: Endocytpse the dissolved products
3rd: Neutralise
4th: Exocytose the products out of the top of the cell

40
Q

what is the process by which bone grows?

A

Appositional growth
Bone is too rigid to grow by a process called interstitial growth

41
Q

describe the process of appositional growth

A
42
Q

do bones spend more time in the active or resting state?

A

resting

43
Q

what are these cells?

A

osteoblasts

44
Q

what are these cells?

A

osteocytes

45
Q

what are these cells?

A

osteogenic cells

46
Q

Rickets

A

Not enough Ca2+ in the diet-> bone stays softer for longer. Osteoblasts keep laying down osteoid but do not calcify it

-when the bones get calcified they’re deformed

Not enough minerals & nutrients to produce Vit D. Need Vit D to absorb Ca2+ through the intestinal wall

47
Q

osteomalacia

A

adults have formed but softer bones. Vit D defficiency

48
Q

how do osteocytes contribute to regulation of Ca2+ and Phosphorus lvls?

A

osteocytes can pull Ca2+ and Phosphorus from the wall of the lacunae or add to the wall of the lacunae. Happens rapidly due to canniculi

49
Q

why are canaliculi positioned in the same direction?

A

when laying down canaliculi cannot be pushed into existing calcified bone, can only push in the direction the bone is growing.

50
Q

name the tissue/cell

A

layer of osteoid that has not been calcified yet

mostly collagen and proteoglycan

51
Q

how do bones grow in length?

A

by the process called Endochondral ossification

Between epiphysis and metaphysis, there is a layer of hyaline cartilage called an epiphyseal/ growth plate.

Chondrocytes in the cartilage can divide and secrete more ECM, making the plate thicker-> pushes epiphysis away from the rest of the bone

The cartilage dies & gets used as a surface to put down new bone. Cartilage is replaced with bone.

Eventually, the rate of cartilage growth drops below the rate at which it is replaced with bone

-> Epiphysis and metaphysis fuse

52
Q

how does the rate of bone growth and reabsorption change throughout your lifetime?

A

children: more growth than absorption
20-35: rate of growth and absorption are ~ the same

over 35: more absorption than growth. Bones become more fragile.

53
Q

by what age are all immature bones replaced with mature?

A

3 yo

54
Q

immature bone(woven) structure

A

collagen fibers inside are wavy, randomly arranged, and not so densely packed( neither are cells or ECM)

not as strong

55
Q

how are collagen fibers laid down in mature/lamellar bone?

A

As osteoblasts deposit new bone onto a surface (appositional growth),
they do so in layers or sheets (lamellae). The collagen fibres are typically
put down in the same direction within a layer, but can alternate up to 90o
out of phase between the layers. This enables bone to withstand forces
from different directions, making it significantly stronger

56
Q

what are the 2 types of lamellar( mature) bone?

A

spongy and compact bone

57
Q

why can trabeculae not be bigger than 0.4 mm in the narrowest dimension?

A

an osteocyte should be within 0.2 mm away from the blood vessel

58
Q

how is collagen layed in the osteon>

A

layers of alternating collagen between lamellae

59
Q

how thick is compact bone?

A

normally > 0.4 mm

60
Q

what is the process that forms primary osteons?

A

appositional growth
primary osteons are formed around existing blood vessels on the surface of the bone( normally in the periosteum)

Bone on either side of the blood vessel grows quickly but slow underneath-> forms crests that fuse to form a tunnel surrounding the blood vessel.

Periosteum layer becomes endosteum

The osteoblasts in the endosteum build lamellae inward filling the tunnel

61
Q

how are secondary osteons formed?

A

by osteoclast activity
secondary osteons are created inside the existing bone

62
Q

what triggers secondary osteon formation?

A

osteocytes die from the insufficient blood supply or there is microdamage in the bone
->chemical signals are released-> monocyte progenitor cells sense the signals and exit the blood vessels and fuse to form the osteoclasts

63
Q

what is the group of osteoclasts that bore through the bone called?

A

cutting cone

64
Q

what is the orientation of the 2ndary osteon formation?

A

the tunnel is oriented along the lines of greater stress through the bone( parts that get damaged more often)

65
Q

how fast does the tunnel of 2ndary osteon progress?

A

~1mm every 20 days

66
Q

how is the blood supply to the new 2ndary osteon layed?

A

a blood vessel grows into the tunnel that is being created.

67
Q

how is the new endosteum formed in the 2ndary osteon?

A

After the tunnel has been created osteogenic cells move in, which differentiate into osteoblasts-> forms new Endosteum-> new lamellae are laid from inside of the tunnel towards the centre.

blood vessel grows in to supply the cells

68
Q

what is the part of the new 2ndary osteon that grows lamellae inwards?

A

closing zone

69
Q

what happens after the 2ndary osteon tunnel is reduced to the typical harvesian canal size?

A

osteoblasts can either die or become bone lining cells ( osteogenic cells) and contribute to the resting endosteum

70
Q

where does most of the appositional growth happen when forming osteons?

A

at endosteum

71
Q

are there osteons in spongy bone?

A

no

72
Q

what is the “cement line”?

A

a line at the junction between the outermost lamella of the new osteon and the preexisting older bone

73
Q

what bone is this?(spongy or compact)

A

spongy bone
no osteons

74
Q

what bone is this?(spongy or compact)

A

compact
osteons present

75
Q

what is this part of the bone?

A

circumferential lamellae

76
Q

what happens to osteon with age?

A

harden

Medsci 142 (32 decks)

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