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MSK Final > Development of limbs > Flashcards

Development of limbs Flashcards

1
Q

What is the origin of muscle in the extremities

A

paraxial mesoderm –> somite

dermamyotome –> myotome –> hypomere –> dorsal lateral hypomere cells migrate to limbs

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2
Q

What is the fate of migrating hypomere cells

A

become dorsal and ventral muscle masses

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3
Q

what is the fate of the dorsal muscle mass?

A

becomes extensors/supinators/abductor muscles of the limbs

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4
Q

what is the fate of the ventral muscle mass?

A

becomes flexors/pronators/ abductors

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5
Q

What are the tendons and bones of the extremities derived from?

A

the lateral plate mesoderm

know this cause it was highlighted heavily on slides

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6
Q

how is bone in the extremities formed? when does it begin

A

lateral plate mesoderm begins the process of endochondral ossification during week 5

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7
Q

What happens during week 5 6 and 7-9 during bone formation

A

week 5-begins
week 6-limb cartilage forms
week 7-9-osteogensis creating long bones

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8
Q

When do limb buds appear?

A

week 4

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9
Q

When does the hand/foot plate appear as well as the beginning of chondrification?

A

week 5

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10
Q

When do the digital rays of the hand form? also limb skeleton is cartilaginous

A

week 6

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11
Q

when do the digital rays of the feet form?

A

week 7

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12
Q

when does osteogenesis take place?

A

week 7

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13
Q

when does limb rotation occur

A

week 7

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14
Q

when are separate digits formed?

A

week 8

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15
Q

what occurs during week 12?

A

primary ossification

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16
Q

What direction are the limbs facing before rotation?

A

ventral surface facing medially

dorsal surface facing laterally

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17
Q

What occurs during rotation of the upper limb?

A

rotates laterally so flexor compartment faces anteriorly and extensor faces posteriorly

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18
Q

what occurs during rotation of the lower limb?

A

rotates medially so flexor compartment faces anteriorly and extensor faces posteriorly

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19
Q

What week do axons from ventral rami innervate muscle? what is this followed by?

A

week 5
sensory axons follow it
NCC turned schwann cells myelinate it

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20
Q

What muscles do axons cranial to the limb innervate?

A

dorsal muscles

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21
Q

What muscles do axons caudal to the limb innervate?

A

ventral muscles

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22
Q

blood supply

A

idk look it up cause i dont get it

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23
Q

What are the 3 parts of the growing arm? which is proximal which is distal?

A

stylopod –> zeugopod –> autopod (proximal to distal)

24
Q

What is secreted by lateral plate mesoderm that begins the process of budding?

A

Fgf10

25
Q

What does Fgf10 do?

A

activates WNT signaling, promotes distal extension of AER and causes it to secrete Fgf8

26
Q

What occurs when WNT signaling is turned on?

A

AER secretes FgF8 –> positive feedvack loop for more Fgf10

27
Q

what is the AER?

A

apical ectodermal ridge (part that moves distally during budding)

28
Q

What occurs if you remove the AER?

A

no limb growth

29
Q

what happens if you have extra AER?

A

extra limb growth, winging

30
Q

what happens if you replace arm mesenchyme with leg mesenchyme but keep the AER intact?

A

you get a normal leg where the arm is supposed to be

31
Q

what happens if you replace arm mesenchyme with non limb mesenchyme?

A

AER regresses and nothing grows

32
Q

what happens if you replace AER with an FGF bead?

A

normal limb growth

33
Q

What causes differentiation into the 3 sections? what happens if one of these is knocked out?

A

HOX genes, if the HOX gene is knocked out that part doesnt form

34
Q

What is the HOX gene for the sytlopod?

A

HOX 9-10

35
Q

What is the HOX gene for the zeugopod?

A

HOX11

36
Q

What is the HOX gene for the autopod?

A

HOX12-13

37
Q

What causes a limb to differentiate cranial from caudal?

A

a ZPA region that is present before budding occurs

38
Q

What does the ZPA region secrete? what does this do?

A

SHH, causes pinky formation, as you move down the gradient it causes other fingers to form

39
Q

What happens if you have too much SHH or an extra ZPA region?

A

polydactyly (multiple fingers) usually an extra pinky

40
Q

You have an extra pinky. What was there too much of during your development?

A

SHH secreted from the ZPA region

41
Q

You knocked out HOX9-10, what doesnt form,?

A

stylopod

42
Q

you knocked out HOX11, what doesnt form?

A

zeugopod

43
Q

You knocked out HOX12-13 what doesnt form

A

autopod

44
Q

What causes dorsal vs ventral differentiation?

A

Lmx1B activates Wnt7a that causes dorsal differentiation

45
Q

How do you form individual digits?

A

BMP signaling causes apoptosis in cells between digits

46
Q

You have decreased BMP expression and are now a good swimmer, why is this?

A

you have webbed fingers you freak (syndactyly)

47
Q

What is meromelia and what causes this?

A

absence of PART of a limb

late or partial loss of FGF signaling

48
Q

what is amelia? cause?

A

total loss of a limb

early or complete loss of FGF signaling

49
Q

What is polydactyly? cause?

A 
extra digits (usually pinky) 
over-expression of SHH, lacks muscle tho
50
Q

What is syndactyly? types? cause of each?

A

fusion of digits
cutaneous (lack of BMP)
osseous (bones, fuse) BMP or HOXD13 mutation

51
Q

what is phacomalacia?

A

absence of long bones

52
Q

what causes phacomalacia that is no longer given to females of child bearing age?

A

thalodimide

53
Q

What does thalodimide do?

A

decreases FGF or HOX signaling

54
Q

what causes split hand/lobster claw/ectrodactyly?

A

decreased FGF8 expression in part of the AER but the rest remains so its split

55
Q

what can cause physical deformities?

A

adhesion between amnion and fetal structures, club foot and stuff

MSK Final (15 decks)

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