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Anatomy term 1 > M Embryology - Limb development > Flashcards

M Embryology - Limb development Flashcards

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1
Q

Which phase and what weeks does limb development occur?

A
  • mid - late embryonic phase

- 4-8weeks

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2
Q

When are limb buds visible?

A

end of week 4

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3
Q

What are the 3 layers of the trilaminar embryonic disc?

A
  1. Ectoderm
  2. Mesoderm
  3. Endoderm
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4
Q

What does the ectoderm give rise to?

A

skin and nervous system

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5
Q

What does the mesoderm give rise to?

A

skeleton and skeletal muscle

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6
Q

What does the endoderm give rise to?

A

Epithelia lining - GI and Resp

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7
Q

Which 2 layers contribute to the formation of limbs?

A
  1. ectoderm

2. mesoderm

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8
Q

Which layer does limb bud formation start from?

A

mesoderm

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9
Q

Which layer is the limb bud core made up of and which part of this layer is it derived from?

A

mesoderm

derived from - lateral plate mesoderm

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10
Q

What is the core of the limb bud covered by and what does this eventually form?

A

ectoderm

skin/epidermis

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11
Q

Why does the mesoderm core condense and what does it differentiate into?

A

to form bone and connective tissues

mesenchyme

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12
Q

Which layer of the mesoderm is skeletal muscle derived from?

A

paraxial mesoderm

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13
Q

What are somites?

A

blocks or subdivisions of paraxial mesoderm

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14
Q

Why are somites important?

A

formation of skeletal muscles

surrounding the vertical column and neural tube

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15
Q

What are the 2 parts of the dermomyotome?

A
  1. dermatome - skin

2. myotome - skeletal muscle

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16
Q

Where is the dermomyotome derived from?

A

somites

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17
Q

What 2 parts does the myotome split into?

A
  1. dorsal part = EPIMERE

2. ventral part = HYPOMERE

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18
Q

What does the epimere form?

A

the muscles of the dorsum/back

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19
Q

What does the hypomere form?

A

the muscles of the thorax and abdomen

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20
Q

Where are the upper limb muscles derived from and what level?

A

hypomere

level of C5-C8

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21
Q

Where are the lower limb muscles derived from and what level?

A

hypomere

level L3-L5

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22
Q

What 2 parts does the hypomere divide into?

A
  1. posterior condensation

2. anterior condensation

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23
Q

What muscles do the posterior condensation include?

A

UPPER LIMB

extensors and supinators

LOWER LIMB

extensors and abductors

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24
Q

What muscles does the anterior condensation include?

A

UPPER LIMB

flexors and pronators

LOWER LIMB

Flexors and adductors

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25
What spinal nerves are associated with the epimere muscles?
dorsal rami
26
What spinal nerves are associated with the hypomere muscles?
ventral rami
27
What are the limb buds initially innervated by?
branches of the ventral primary rami of the spinal nerves
28
What is the upper limb innervated by?
Brachial plexus | C5-T1
29
What is the lower limb innervated by?
lumbosacral plexus | L4-S3
30
Why does the anterior and posterior compartment of limbs have different nerve supplies?
As the spinal nerves of the limb bud migrates and splits into anterior and posterior branches.
31
Why is limb rotation necessary?
makes sure limbs don't meet each other
32
When does limb rotation occur (which weeks)?
between 6 and 8 weeks
33
How do the upper limbs rotate and why do they rotate in this way?
90 degrees laterally flexors lie anteriorly
34
How od the lower limbs rotate and why do they rotate in this way?
90 degrees medially flexors lie posteriorly
35
What effect does limb rotation have on the dermatomes?
causes sensory dermatomes to spiral round limbs
36
What are dermatomes and what injury does it allow to be tested?
band of skin supplied by one pair of spinal nerves spinal cord injuries - test levels of the spinal cord
37
NOTE
learn dermatomes
38
What 3 axes does the limb develop along?
1. proximodistal 2. cranocaudal 3. dorsoventral
39
Where does the proximodistal axis run and what is it's role?
RUN shoulder to hip to hand/foot ROLE lengthening limb away from the body
40
Where does the craniocaudal axis make sure and what is it's role?
MAKES SURE thumb is most cranial digit and the little finger most caudal ROLE makes sure digits (fingers and toes) end up in correct position
41
What does the dorsoventral axis do?
Makes sure the palm of the hand and the sole of the foot are ventral = SOFT Makes sure the knuckle side of hand/foot is dorsal = HARD
42
What is formed in the proximodistal outgrowth?
apical ectodermal ridge
43
What does the lateral plate mesoderm secrete?
Fibroblast growth factor - Fgf 10
44
What does Fgf-10 induce and what does this form?
1. thickening of the overlying ectoderm along the tip of the limb bud this forms the Apical ectodermal ridge - AER
45
What does the apical ectodermal ridge do?
drives growth of limb bud
46
What does the apical ectodermal ridge express?
Fibroblastic growth factors 1. Fgf 4 2. Fgf 8
47
What does Fgf-4 and Fgf-8 cause?
- rapid proliferation of the mesenchymal cells underlying the apical ectodermal ridge - forms the PROGRESS ZONE
48
What does the progress zone do?
maintains proximodistal outgrowth of limb
49
What happens if you remove the apical ectodermal ridge?
the rest of the limb with halt growth
50
What controls dorsoventral patterning, what does it do and what is it expressed by?
Wnt7 controls morphology of palm and nails by dorsal ectoderm
51
What inhibits Wnt7 and where is it derived from?
Engrailed-1 ventral ectoderm
52
What happens if you remove Wnt7?
palmar structures form on back of the hand
53
What is craniocaudal patterning controlled by?
Zone of polarising activity (ZPA) - small region of mesenchyme in the caudal limb part - where sonic the hedgehog (SHH) is expressed
54
What does sonic the hedgehog (SHH) do ?
HIGH CONC induces formation of caudal structures - little finger LOW CONC induces formation of cranial structures - thumb
55
Where does Sonic the hedgehog diffuse from and in which direction?
From - ZPA Cranial direction
56
What does transplantation of ZPA induce?
mirror image polydactyly
57
In which week does digit formation occur?
week 6
58
How are fingers and toes formed?
Apoptosis in apical ectodermal ridge
59
What types of limb malformations are there? (7)
1. amelia 2. meromelia 3. phocomelia 4. phenomelia 5. syndactyly 6. polydactly 7. ectrodactyly
60
Amelia - what is it and what is it due to?
complete absence of a limb lack of Fgf signalling
61
Meromelia - what is it and what is it due to?
partial absence of a limb later/partial loss of Fgf signalling or AER removed less severe
62
Phocomelia - what is it and what is it due to?
digits develop prematurely and proximal elements of limbs are absent - flipper limb - shortened limbs lack of proximodistal growth - Thalidomide
63
What is thalidomide used to treat nowadays?
Leprosy and HIV
64
Syndactyly - what it is and what is it caused by?
fused digits failure of apoptosis
65
Polydactyly - what is it and what is caused by?
extra digits inappropriate SHH expression
66
Ectrodactyly - what is it and what is it caused by?
split hand/foot - lobster claw deformity failure of middle of the AER formation hence defect in proximodistal outgrowth

Anatomy term 1 (10 decks)

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