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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
Limb development What happens in carnigie stage 13
Lower limb buds appear (between week 4 and 5)
26
Limb development What happens in caringie stage 15
The hand plates form and the digital rays are visible (end of week 5)
27
Elongation of limb buds Where is the AER located
along the border between dorsal and ventral limb ectoderm
28
Formation of limb skeleton When does the mesenchyme turn into cartilage?
in the 5th week
29
Formation of limb skeleton What does the the chondrification center do
it turns the mesenchyme into cartilage
30
Positional changes of developing limbs Rotation of upper limbs
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
31
Differentiation of Limb buds Where is Retinoic acid highly concentrated
at the proximal aspect of the limb
32
Limb development What happens in carnigie stage 21
Hands and feet approach each other; fingers and toes are free and longer; toes are distinct but webbed
33
Differentiation of Limb buds Where does retinoic acid come from
the somites
34
Formation of limb skeleton Where are secondary ossifcation centers located at birth
Distal femur and proximal tibia
35
Elongation of limb buds How does AER promote limb bud elongation?
it induces the adjacent mesenchyme to remain undifferentiated and to rapidly proliferate; occurs in the progress zone
36
Differentiation of Limb buds Where is Retinoic acid minimally concentrated
at the distal aspect of the limb
37
Formation of limb skeleton What is the epiphysis of the long
the ends of the long bone
38
Formation of limb muscle What are skeletal muscles of limbs formed from
myogenic precursor cells (including migrated somite cells)
39
Lower limb buds form adjacent to ___________ and ___________ vertebral segments
caudal lumbar; cranial sacral
40
What determines the craniocaudal location of limb buds
Hox genes
41
Development of limb buds When are separate digits formed in the upper limb
about day 52
42
What are the three axes of limb development
Proximodistal , Craniocaudal, Dorsoventral
43
Differentiation of Limb buds What does retinoic acid contribute to?
limb differentiation
44
Development of limb buds What is the third step?
The loose mesenchyme that makes up the webbed intervals of the digital rays undergoes apoptosis, which forms notches then separate digits
45
Signaling in limb development What does HoxC -8,-9,-10 stimulate and repress
it stimulates Tbx-4 but represses Tbx-5
46
Formation of limb skeleton What is the epiphyseal cartialage plate
cartilage plate between the shaft and each end
47
Positional changes of developing limbs Rotation of lower limbs
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
Development of limb buds What is the first step
The distal portion of the limb buds flatten around the AER forming the hand+foot plate
49
Differentiation of Limb buds Order of differentiation
stylopodium -> zeugopodium -> autopodium
50
What does the surface ectoderm eventually become
the skin
51
What is cutaneous syndactyly
failure of digits to separate due to failure of cellular apoptosis
52
What is polydactyly
More than 5 digids on a limb
53
Elongation and differentiation along the dorsoventral axis Which protien is expressed by the dorsal non AER ectoderm
WNT-7a
54
Signaling in limb development Where are Hox genes expressed
in lateral plate mesoderm
55
Cell contribution to limb development Lateral plate mesoderm
contibutes to formation of the skeleton, CT, and some BV's
56
Limb development What happens in caringie stage 12
the upper limb buds appear (week 4)
57
Cell contribution to limb development Neural crest cells
contribute to formation of pigment cells, sensory axons, and schwaan cells
58
Elongation of limb buds Where is the zone of polarizing activity found (ZPA)
at the proximal, caudal border of the limb
59
Formation of limb skeleton When does ossification of limb long bones begin
at the end of the embryonic period (day 56)
60
Limb development What happens in carnigie stage 16
The foot plates are formed (week 6)
61
Limb development What happens in carnigie stage 17
Digital rays are clearly visible in hand plates (end of week 6)
62
Elongation and differentiation along the dorsoventral axis What does LMX-1 expression determine
that the extensors are located dorsally
63
Elongation and differentiation along the dorsoventral axis What does WNT-7a induce?
expression of LMX-1
64
Elongation and differentiation along the dorsoventral axis Which protien is expressed by the ventral non-AER ectoderm
Engrailed-1 (En-1)
65
Signaling in limb development What do Tbx-5 and Tbx-4 stimulate
Fibroblast growth factors (FGF's)
66
Development of limb buds When are notches formed in the lower limb
about day 49
67
Differentiation of Limb buds Where is FGF minimally concentrated?
at the proximal aspect of the limb
68
Elongation of limb buds What does AER promote
Limb bud elongation
69
Elongation of limb buds What happens as the limb buds grow?
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
When do upper and lower limb buds form
towards the end of the 4th week
71
Elongation and differentiation along the craniocaudal axis What happens to the ZPA
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
Limb development What happens in carnigie stage 22
toes are free and longer
73
Formation of limb skeleton When are primary ossification centers found in all long bones
by week 12
74
Limb development What happens in carnigie stage 18
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
Signaling in limb development Where is HoxC-8,-9,-10 expressed?
Near the upper location where the lower limbs are formed
76
Limb development What happens in carnigie stage 20
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
Signaling in limb development Where is Hox-4/5 expressed
near the location where the upper limbs are formed
78
Elongation and differentiation along the dorsoventral axis What does Engrailed-1 expression deterimine
that the flexors are located ventrally

Embryology (14 decks)

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