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Anatomy term 1 > M Embryology - Limb development > Flashcards

M Embryology - Limb development Flashcards

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
Q

What spinal nerves are associated with the epimere muscles?

A

dorsal rami

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26
Q

What spinal nerves are associated with the hypomere muscles?

A

ventral rami

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27
Q

What are the limb buds initially innervated by?

A

branches of the ventral primary rami of the spinal nerves

28
Q

What is the upper limb innervated by?

A

Brachial plexus

C5-T1

29
Q

What is the lower limb innervated by?

A

lumbosacral plexus

L4-S3

30
Q

Why does the anterior and posterior compartment of limbs have different nerve supplies?

A

As the spinal nerves of the limb bud migrates and splits into anterior and posterior branches.

31
Q

Why is limb rotation necessary?

A

makes sure limbs don’t meet each other

32
Q

When does limb rotation occur (which weeks)?

A

between 6 and 8 weeks

33
Q

How do the upper limbs rotate and why do they rotate in this way?

A

90 degrees laterally

flexors lie anteriorly

34
Q

How od the lower limbs rotate and why do they rotate in this way?

A

90 degrees medially

flexors lie posteriorly

35
Q

What effect does limb rotation have on the dermatomes?

A

causes sensory dermatomes to spiral round limbs

36
Q

What are dermatomes and what injury does it allow to be tested?

A

band of skin supplied by one pair of spinal nerves

spinal cord injuries - test levels of the spinal cord

37
Q

NOTE

A

learn dermatomes

38
Q

What 3 axes does the limb develop along?

A
  1. proximodistal
  2. cranocaudal
  3. dorsoventral
39
Q

Where does the proximodistal axis run and what is it’s role?

A

RUN

shoulder to hip to hand/foot

ROLE

lengthening limb away from the body

40
Q

Where does the craniocaudal axis make sure and what is it’s role?

A

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
Q

What does the dorsoventral axis do?

A

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
Q

What is formed in the proximodistal outgrowth?

A

apical ectodermal ridge

43
Q

What does the lateral plate mesoderm secrete?

A

Fibroblast growth factor - Fgf 10

44
Q

What does Fgf-10 induce and what does this form?

A
  1. thickening of the overlying ectoderm along the tip of the limb bud

this forms the Apical ectodermal ridge - AER

45
Q

What does the apical ectodermal ridge do?

A

drives growth of limb bud

46
Q

What does the apical ectodermal ridge express?

A

Fibroblastic growth factors

  1. Fgf 4
  2. Fgf 8
47
Q

What does Fgf-4 and Fgf-8 cause?

A
  • rapid proliferation of the mesenchymal cells underlying the apical ectodermal ridge
  • forms the PROGRESS ZONE
48
Q

What does the progress zone do?

A

maintains proximodistal outgrowth of limb

49
Q

What happens if you remove the apical ectodermal ridge?

A

the rest of the limb with halt growth

50
Q

What controls dorsoventral patterning, what does it do and what is it expressed by?

A

Wnt7

controls morphology of palm and nails

by dorsal ectoderm

51
Q

What inhibits Wnt7 and where is it derived from?

A

Engrailed-1

ventral ectoderm

52
Q

What happens if you remove Wnt7?

A

palmar structures form on back of the hand

53
Q

What is craniocaudal patterning controlled by?

A

Zone of polarising activity (ZPA)

  • small region of mesenchyme in the caudal limb part
  • where sonic the hedgehog (SHH) is expressed
54
Q

What does sonic the hedgehog (SHH) do ?

A

HIGH CONC

induces formation of caudal structures - little finger

LOW CONC

induces formation of cranial structures - thumb

55
Q

Where does Sonic the hedgehog diffuse from and in which direction?

A

From - ZPA

Cranial direction

56
Q

What does transplantation of ZPA induce?

A

mirror image polydactyly

57
Q

In which week does digit formation occur?

A

week 6

58
Q

How are fingers and toes formed?

A

Apoptosis in apical ectodermal ridge

59
Q

What types of limb malformations are there? (7)

A
  1. amelia
  2. meromelia
  3. phocomelia
  4. phenomelia
  5. syndactyly
  6. polydactly
  7. ectrodactyly
60
Q

Amelia - what is it and what is it due to?

A

complete absence of a limb

lack of Fgf signalling

61
Q

Meromelia - what is it and what is it due to?

A

partial absence of a limb

later/partial loss of Fgf signalling or AER removed

less severe

62
Q

Phocomelia - what is it and what is it due to?

A

digits develop prematurely and proximal elements of limbs are absent

  • flipper limb
  • shortened limbs

lack of proximodistal growth - Thalidomide

63
Q

What is thalidomide used to treat nowadays?

A

Leprosy and HIV

64
Q

Syndactyly - what it is and what is it caused by?

A

fused digits

failure of apoptosis

65
Q

Polydactyly - what is it and what is caused by?

A

extra digits

inappropriate SHH expression

66
Q

Ectrodactyly - what is it and what is it caused by?

A

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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