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Embryology > T14- Limb development > Flashcards

T14- Limb development Flashcards

1
Q

Differentiation of Limb buds

Where is FGF highly concentrated

A

at the distal aspect of the limb

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2
Q

Upper limb buds form ___________ to _________ vertebral segments

A

adjacent; cervical

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3
Q

What does the mesenchymal core of the limb bud eventually become

A

the bones and muscles

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4
Q

Signaling in limb development

FGF-10 ___________ FGF-8 which is in the overlying _________. A _______ feedback loop ensues

A

stimulates; ectoderm; positive

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5
Q

Development of limb buds

When are notches formed in the upper limb

A

about day 46

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6
Q

What do limb buds consist of initially?

A

a mesenchymal core and a layer of surface ectoderm

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7
Q

Development of limb buds

What is the second step

A

Condensation of mesenchymal core tissue in plates to form digital rays that each have an AER tip

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8
Q

Cell contribution to limb development

Neural Tube cells

A

contribute to formation of motor axons

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9
Q

Formation of limb muscle

Where do myogenic precursor cells first cluster

A

at the base of the limb buds

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10
Q

Development of limb buds

When does digital ray formation in the hands happen

A

In the 6th week (day 41)

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11
Q

Signaling in limb development

What does Hox-4/5 stimulate?

A

Tbx-5

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12
Q

Elongation and differentiation along the craniocaudal axis

What does the ZPA express

A

Sonic hedgehog

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13
Q

Limb development

What happens in carnigie stage 19

A

The limbs extend ventrally (end of week 7)

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14
Q

Formation of limb skeleton

What is the diaphysis of the long bone

A

the shaft of the long bone

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15
Q

Formation of limb skeleton

What happens by the end of week 6 (day 42)

A

entire limb skeleton is a hyaline cartilage bone model

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16
Q

Development of limb buds

When does digital ray formation in the feet happen?

A

In the 7th week (day 46)

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17
Q

Cell contribution to limb development

Somites

A

contribute to formation of myoblasts and endothelial cell precursors

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18
Q

What is complex (osteus) syndactyly

A

less common than cutaneous syndactyly and is a result of failure of the digital rays to separate

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19
Q

Elongation and differentiation along the craniocaudal axis

What does the SHH that the ZPA expresses ensure

A

SHH ensures that the digits appear in the correct order (thumb on cranial side and pinky on caudal side)

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20
Q

Positional changes of developing limbs

Initial state of limbs

A

Limbs initially extend ventrally; palms/soles face each other; elbows/knees point laterally

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21
Q

Elongation of limb buds

What happens to the apex of each limb bud in response to the FGF positive feed back loop

A

apical ectodermal ridge (AER) forms

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22
Q

Formation of limb muscle

How do myogenic precursor cells differentiate

A

they migrate into limb buds, undergo epitheliomesenchymal transformation and differentiate into myoblasts

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23
Q

Development of limb buds

When are separate digits formed in the lower limb

A

about day 55

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24
Q

Formation of limb muscle

How are extensors and flexors formed

A

myoblasts aggregate on either side of long bone

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25
Q

Limb development

What happens in carnigie stage 13

A

Lower limb buds appear (between week 4 and 5)

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26
Q

Limb development

What happens in caringie stage 15

A

The hand plates form and the digital rays are visible (end of week 5)

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27
Q

Elongation of limb buds

Where is the AER located

A

along the border between dorsal and ventral limb ectoderm

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28
Q

Formation of limb skeleton

When does the mesenchyme turn into cartilage?

A

in the 5th week

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29
Q

Formation of limb skeleton

What does the the chondrification center do

A

it turns the mesenchyme into cartilage

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30
Q

Positional changes of developing limbs

Rotation of upper limbs

A

Upper limbs rotate externally 90 degrees resulting in:

  • elbows pointing caudally
  • flexor muscles found along anterior limb surface
  • extensor muscles found along posterior limb surface
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31
Q

Differentiation of Limb buds

Where is Retinoic acid highly concentrated

A

at the proximal aspect of the limb

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32
Q

Limb development

What happens in carnigie stage 21

A

Hands and feet approach each other; fingers and toes are free and longer; toes are distinct but webbed

33
Q

Differentiation of Limb buds

Where does retinoic acid come from

A

the somites

34
Q

Formation of limb skeleton

Where are secondary ossifcation centers located at birth

A

Distal femur and proximal tibia

35
Q

Elongation of limb buds

How does AER promote limb bud elongation?

A

it induces the adjacent mesenchyme to remain undifferentiated and to rapidly proliferate; occurs in the progress zone

36
Q

Differentiation of Limb buds

Where is Retinoic acid minimally concentrated

A

at the distal aspect of the limb

37
Q

Formation of limb skeleton

What is the epiphysis of the long

A

the ends of the long bone

38
Q

Formation of limb muscle

What are skeletal muscles of limbs formed from

A

myogenic precursor cells (including migrated somite cells)

39
Q

Lower limb buds form adjacent to ___________ and ___________ vertebral segments

A

caudal lumbar; cranial sacral

40
Q

What determines the craniocaudal location of limb buds

A

Hox genes

41
Q

Development of limb buds

When are separate digits formed in the upper limb

A

about day 52

42
Q

What are the three axes of limb development

A

Proximodistal , Craniocaudal, Dorsoventral

43
Q

Differentiation of Limb buds

What does retinoic acid contribute to?

A

limb differentiation

44
Q

Development of limb buds

What is the third step?

A

The loose mesenchyme that makes up the webbed intervals of the digital rays undergoes apoptosis, which forms notches then separate digits

45
Q

Signaling in limb development

What does HoxC -8,-9,-10 stimulate and repress

A

it stimulates Tbx-4 but represses Tbx-5

46
Q

Formation of limb skeleton

What is the epiphyseal cartialage plate

A

cartilage plate between the shaft and each end

47
Q

Positional changes of developing limbs

Rotation of lower limbs

A

Lower limbs rotate internally 90 degrees resulting in:

  • knees pointing cranially
  • flexor muscles being found along the posterior limb surface
  • extensor muscles being found along the anterior limb surface
48
Q

Development of limb buds

What is the first step

A

The distal portion of the limb buds flatten around the AER forming the hand+foot plate

49
Q

Differentiation of Limb buds

Order of differentiation

A

stylopodium -> zeugopodium -> autopodium

50
Q

What does the surface ectoderm eventually become

A

the skin

51
Q

What is cutaneous syndactyly

A

failure of digits to separate due to failure of cellular apoptosis

52
Q

What is polydactyly

A

More than 5 digids on a limb

53
Q

Elongation and differentiation along the dorsoventral axis

Which protien is expressed by the dorsal non AER ectoderm

A

WNT-7a

54
Q

Signaling in limb development

Where are Hox genes expressed

A

in lateral plate mesoderm

55
Q

Cell contribution to limb development

Lateral plate mesoderm

A

contibutes to formation of the skeleton, CT, and some BV’s

56
Q

Limb development

What happens in caringie stage 12

A

the upper limb buds appear (week 4)

57
Q

Cell contribution to limb development

Neural crest cells

A

contribute to formation of pigment cells, sensory axons, and schwaan cells

58
Q

Elongation of limb buds

Where is the zone of polarizing activity found (ZPA)

A

at the proximal, caudal border of the limb

59
Q

Formation of limb skeleton

When does ossification of limb long bones begin

A

at the end of the embryonic period (day 56)

60
Q

Limb development

What happens in carnigie stage 16

A

The foot plates are formed (week 6)

61
Q

Limb development

What happens in carnigie stage 17

A

Digital rays are clearly visible in hand plates (end of week 6)

62
Q

Elongation and differentiation along the dorsoventral axis

What does LMX-1 expression determine

A

that the extensors are located dorsally

63
Q

Elongation and differentiation along the dorsoventral axis

What does WNT-7a induce?

A

expression of LMX-1

64
Q

Elongation and differentiation along the dorsoventral axis

Which protien is expressed by the ventral non-AER ectoderm

A

Engrailed-1 (En-1)

65
Q

Signaling in limb development

What do Tbx-5 and Tbx-4 stimulate

A

Fibroblast growth factors (FGF’s)

66
Q

Development of limb buds

When are notches formed in the lower limb

A

about day 49

67
Q

Differentiation of Limb buds

Where is FGF minimally concentrated?

A

at the proximal aspect of the limb

68
Q

Elongation of limb buds

What does AER promote

A

Limb bud elongation

69
Q

Elongation of limb buds

What happens as the limb buds grow?

A

proximal cells move further away from the progress zone and because of this, they are under less influence by the AER so they will begin to differentiate

70
Q

When do upper and lower limb buds form

A

towards the end of the 4th week

71
Q

Elongation and differentiation along the craniocaudal axis

What happens to the ZPA

A

As the limbs grow along the proximodistal axis, the ZPA moves distally so that it remains in close contact with the caudal ectoderm of the AER

72
Q

Limb development

What happens in carnigie stage 22

A

toes are free and longer

73
Q

Formation of limb skeleton

When are primary ossification centers found in all long bones

A

by week 12

74
Q

Limb development

What happens in carnigie stage 18

A

digital rays are clearly visible in the foot plates and the elbow reigon is visible; there are notches between digital rays in the hand (week 7)

75
Q

Signaling in limb development

Where is HoxC-8,-9,-10 expressed?

A

Near the upper location where the lower limbs are formed

76
Q

Limb development

What happens in carnigie stage 20

A

The upper limbs are longer and are bent at the elbows; fingers are distinct but webbed; notches between digital rays in the feet (end of week 7, beginning of week 8)

77
Q

Signaling in limb development

Where is Hox-4/5 expressed

A

near the location where the upper limbs are formed

78
Q

Elongation and differentiation along the dorsoventral axis

What does Engrailed-1 expression deterimine

A

that the flexors are located ventrally

Embryology (14 decks)

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