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ANAT1003 test 2 > Limb development > Flashcards

Limb development Flashcards

1
Q

what gives rise to the humerus?

A

stylopod

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2
Q

what gives rise to the radius and ulna?

A

zeugopod

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3
Q

what gives rise to the wrist bones, palm bones and digit bones?

A

distal autopod

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4
Q

is the back of the hand dorsal or ventral?

A

dorsal

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5
Q

is the palm of the hand dorsal or ventral?

A

ventral

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6
Q

what is grieg syndrome?

A

polydactyly and syndactyly

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7
Q

what causes grieg syndrome?

A

mutation in GL13

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8
Q

what is apert syndrome?

A

syndactyly

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9
Q

what causes apert syndrome?

A

mutations in FGFR2

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10
Q

what is holt-oram syndrome?

A

phocomelia

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11
Q

what causes holt-oram syndrome?

A

mutations in TBX5

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12
Q

what did thalidomide cause?

A

phocomelia

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13
Q

when was thalidomide given to women?

A

1956-1961

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14
Q

how many babies did thalidomide affect?

A

around 2000 (only 500 survived)

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15
Q

when do forelimb bids form?

A

24th day

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16
Q

when do hindlimbs form?

A

28th day

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17
Q

what are the limb buds formed of?

A

epidermal jacket enclosing lateral plate mesoderm

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18
Q

what does the mesoderm form in the limbs?

A

most of tissues (bone, tendons, ligaments, dermis, muscle sheaths and blood vessels)

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19
Q

what is the position of the limb buds determined by?

A

hox genes

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20
Q

what does AER stand for?

A

acpical ectodermal ridge

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21
Q

where does the AER form?

A

at the distal end of the limb bud

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22
Q

what type of cells is the AER made of?

A

columnar cells

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23
Q

what are TBX5 and TBX4?

A

transcription factors

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24
Q

where is TBX5 transcribed?

A

forelimbs

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25
Q

where is TBX4 transcribed?

A

hindlimbs

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26
Q

what do mutations in TBX5 cause?

A

Holt-Oram syndrome (only affects forelimbs)

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27
Q

what do mutations in TBX4 cause?

A

patella syndrome (affects bones of hips and legs)

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28
Q

what forms limb muscle?

A

hypaxial myotome

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29
Q

when do mytome cells migrate into limb buds?

A

5th week of development

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30
Q

what does the myotome initially form?

A

large dorsal and ventral condensations

31
Q

what does the dorsal muscle mass form?

A

extensors and supinators of forelimb and extensors and abductors of hindlimbs

32
Q

what does the ventral muscle mass form?

A

flexors and pronators of forelimb and flexors and adductors of hindlimb

33
Q

which spinal nerves innervate the muscles of the forelimbs?

A

C5-T2

34
Q

which spinal nerves innervate the muscle of the hindlimbs?

A

L4-S3

35
Q

how many motor neurons innervate a single myotome during development?

A

at least 2

36
Q

how many motor neurons innervate a single mytome in an adult?

A

1 (all but one retracted soon after birth)

37
Q

which bones differentiate first?

A

humerus and femur

38
Q

what is the order of differentiation?

A

humerus/femur, radius + ulna/tibia + fibula, carpals/tarsels, metacarpals/metatarsels and finally, phalanges

39
Q

which digit differentiates first?

A

4

40
Q

what is the order of digit differentiation?

A

4, 3, 2 then 1 and 5 at same time

41
Q

what is required for limb outgrowth?

A

AER

42
Q

what will the removal of AER create?

A

a distally truncated limb as it will stop limb bud outgrowth

43
Q

what is AER the source of?

A

mitogen

44
Q

what is the mitogen responsible for promoting?

A

cell division in limb bud mesenchyme

45
Q

what is a mitogen?

A

an extracellular system that instructs cells to undergo mitosis

46
Q

if AER is removed early, what is formed?

A

the humerus

47
Q

if AER is removed late, what is formed?

A

the humerus, radius and ulna

48
Q

what is the mitogen involved in limb bud outgrowth?

A

FGF

49
Q

what does FGF do in the limb?

A

it diffuses into the limb bud mesenchyme and stimulates call proliferation, thereby promoting limb outgrowth

50
Q

FGF is essential for limb outgrowth. true or false?

A

true

51
Q

does FGF act as a morphogen?

A

there is some evidence to suggest this - phalanges receive highest concentration, radius and ulna receive the lowest and the humerus grows irrespective of FGF

52
Q

John Saunders grafted a posterior mesenchyme into an anterior mesenchyme. what was formed?

A

a duplicate set of digits, with mirror image symmetry

53
Q

what is the organising centre for patterning the anterior-posterior axis of the limb bud?

A

the posterior margin, also known as the ZPA

54
Q

what does ZPA stand for?

A

zone of polarising activity

55
Q

what digit forms in the absence of a morphogen?

A

the thumb

56
Q

what is the morphogen in the limb buds?

A

SHH

57
Q

where is shh expressed?

A

in the ZPA

58
Q

shh mimics ZPA grafts when expressed in anterior mesenchyme. true or false?

A

true

59
Q

how does shh specify digits?

A

in a concentration dependant manner

60
Q

shh is required for limb development. true or false?

A

true

61
Q

what defect can shh cause?

A

preaxial polydactyly

62
Q

what is preaxial polydactyly?

A

an extra digit on the side of the thumb

63
Q

what type of mutation causes preaxial polydactyly?

A

gain-of-function mutation which affects the enhancer controlling shh production in the zpa

64
Q

what is acheiropodia?

A

absense of distal elements of the limbs

65
Q

what causes acheiropodia?

A

deletion of DNA that controls expression of shh in zpa

66
Q

what removes the flaps of skin that connect the digits of an embryo?

A

apoptosis

67
Q

what is apoptosis?

A

programmed cell death

68
Q

what is syndactyly?

A

when two or more digits are fused together

69
Q

what causes syndactyly?

A

lack of apoptosis in interdigital region during embryogenesis

70
Q

between which digits is syndactyly most common?

A

3rd and 4th

71
Q

what are limb buds formed by?

A

the proliferating cells of the outer somatopleuric layer of the lateral plate mesoderm

72
Q

what attracts hypaxial myoblasts to the limb bud?

A

hepatocyte growth factor (HGF)

73
Q

what secrets HGF?

A

limb bud mesenchyme

ANAT1003 test 2 (8 decks)

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