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Year 2 Term 1 Movement > Lecture 1: Embryology Limbs > Flashcards

Lecture 1: Embryology Limbs Flashcards

1
Q

Between which weeks in embryonic development does limb development occur?

A

Weeks 4-8

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2
Q

When do limb buds first appear?

A

End of week 4

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3
Q

Where do limb buds first appear?

A

As outpouchings from the ventrolateral body wall

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4
Q

Do the upper limbs develop a few days ahead or behind the lower limbs?

A

Ahead

As with most embryological development, cranial development is faster than caudal development

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5
Q

What are the 3 layers in the trilaminar embryonic disc?

A

Ectoderm
Mesoderm
Endoderm

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6
Q

What 3 parts is the mesoderm divided into to?

A

Paraxial mesoderm (closest to notochord)
Intermediate mesoderm
Lateral plate mesoderm

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7
Q

Which 2 germ layers contribute to limb development?

A

Ectoderm and mesoderm

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8
Q

What do the limb buds initially consist of?

A

A core of tissue derived from lateral plate mesoderm

Surrounded by ectoderm which forms the overlying skin - the epidermis

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9
Q

What does the lateral plate mesoderm core of the limb buds differentiate into and what does this go on to form?

A

Differentiates into mesenchyme

This mesenchyme will form the bones and connective tissue of the limbs

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10
Q

From what part of the mesoderm is the skeletal muscle of the limbs derived from?

A

Paraxial mesoderm

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11
Q

What does the paraxial mesoderm divide into either side of the neural tube?

A

Somites

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12
Q

The somites divide into 2 parts, what is the ventral part called and what does this go on to form?

A

Ventral part of the somites forms the sclerotome which forms the vertebral column

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13
Q

The somites divide into 2 parts what is the dorsolateral part called and what does this go on to form?

A

Dorsolateral part forms the dermomyotome
The dermamyotome divides into the dermatome and the myotome
The dermatome gives rise to the dermis of the skin and the myotome gives rise to the skeletal muscles

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14
Q

The myotome derived from the somites differentiates to form 2 components, what are they called?

A

1) Dorsal epimere

2) Ventral hypomere

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15
Q

What does the dorsal epimere from the myotome form and what is it innervated by?

A

Forms the back muscles which are innervated by the dorsal rami of the spinal nerves

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16
Q

What does the ventral hypomere of the myotome form and what is it innervated by?

A

Forms the muscles of the thoracic and abdominal walls and the muscles of the limbs which are innervated by the ventral rami of the spinal nerves

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17
Q

The muscles of the limbs are formed from what part of the myotome?

A

Ventral hypomere

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18
Q

At how many weeks has the myotome differentiated into the 2 components the epimere and hypomere?

A

5 weeks

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19
Q

The skeletal muscle of the upper limb is derived from the hypomere from which vertebral level?

A

C5-C8

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20
Q

The skeletal muscle of the lower limb is derived from the hypomere from which vertebral level?

A

L3-L5

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21
Q

As the hypomeres migrate to the limb they divide into what 2 parts?

A

Anterior condensation

Posterior condensation

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22
Q

At how many weeks has the hypomere migrated to the limbs and divided into an anterior and posterior condensation?

A

7 weeks

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23
Q

What do the anterior and posterior condensations of the hypomere form in the upper limb?

A

Posterior - Extensors and supinators of the upper limbs

Anterior - Flexors and pronators of the upper limb

24
Q

What do the anterior and posterior condensations of the hypomere form in the lower limb?

A

Posterior - Extensors and abductors of lower limb

Anterior - Flexors and adductors of lower limb

25
Q

The upper limb is innervated by what plexus?

A

Brachial plexus

26
Q

The brachial plexus receives nerves from which vertebral level?

A

C5-T1

27
Q

The lower limb is innervated by which plexus?

A

Lumbosacral plexus

28
Q

The lumbosacral plexus receives nerves from which vertebral level?

A

L4-S3

29
Q

Why do anterior and posterior compartments of the limbs have different nerve supplies?

A

As the ventral rami of the spinal nerves migrate into the limb bud with the developing musculature, they split into anterior and posterior branches
Thus an anterior branch supplying the muscles of the anterior compartment
And a posterior branch supplying the muscles of the posterior compartment

30
Q

Between which weeks does limb rotation occur?

A

Between 6th and 8th weeks

31
Q

Which way do the upper limbs rotate? Where do the flexors ultimately lie?

A

90 degrees laterally

Flexors lie anteriorly

32
Q

Which way do the lower limbs rotate? Where do the flexors ultimately lie?

A

90 degrees medially

Flexors lie posteriorly

33
Q

What causes the sensory dermatomes to spiral around the limbs?

A

Limb rotation between weeks 6 and 8

34
Q

Which 3 axis does limb development occur along?

A

1) Proximodistal - outwards from the body
2) Craniocaudal - ie the thumb is most cranial and the little finger most caudal
3) Dorsoventral - the palm of the hand and the sole of the foot are ventral and the knuckle side of the hand/foot are dorsal

35
Q

What is the name of the growth factor secreted by the lateral plate mesoderm forming the mesenchymal core, and what does this cause the development of?

A

Secretes fibroblastic growth factor 10 (Fgf 10)
This induces the thickening of the overlying ectoderm over the tip of the limb bud to form the apical ectodermal ridge - AER

36
Q

What is secreted by the apical ectodermal ridge and what does this cause?

A

Fibroblastic growth factors 4 and 8, (Fgf 4 and 8)
This causes rapid proliferation of mesenchymal cells underlying the AER - the progress zone
The progress zone maintains proximodistal outgrowth of the limb

37
Q

What 3 growth factors are involved in controlling the proximodistal outgrowth of the developing limb and wat are they secreted by?

A

Fibroblastic growth factor 10 - mesenchyme (lateral plate mesoderm)
Fibroblastic growth factors 4 and 8 - Apical ectodermal ridge

38
Q

Which experiment proves the role played by the AER in controlling the proximodistal growth of the developing limb?

A

In a chick
If the AER is removed from the developing limb then this hastens the proximodistal growth of the developing limb and it will not develop further

39
Q

Which experiment proves the role of Fgf 4,8 and 10 in limb development?

A

If beads soaked in Fgf are implanted in a developing embryo close to the normal sights of limb development this results in supernumerary limbs

40
Q

How is dorsoventral patterning controlled in limb development?

A

The dorsal ectoderm expresses Wnt 7 which induces the development of nails and knuckles
The ventral mesoderm expresses Engrailed 1 which inhibits Wnt 7 and encourages the development of palms and soles

41
Q

Which 2 proteins are involved in the control of dorsoventral patterning in the developing limb?

A

Wnt 7

Engrailed 1

42
Q

Which experiment proves the role of Wnt 7 in dorsoventral patterning in the developing limb?

A

Wnt7 knockout mice form foot pads on the dorsal aswell as the ventral wall

43
Q

What is the name of the region involved in controlling the craniocaudal limb development and where is it located?

A

Called the zone of polarising activity (ZPA)

Small region of mesenchyme located in the caudal region of the limb bud

44
Q

Which protein is expressed by the ZPA that controls craniocaudal limb development?

A

Sonic Hedgehog (Shh)

45
Q

How does the ZPA and Shh control craniocaudal limb development?

A

Shh is expressed by the ZPA
Shh diffuses in the cranial direction as it does so the concentration decreases
High concentrations of Shh induces formation of caudal structure eg. little finger and 4th digit/little toes
Low concentrations induce the formation of cranial structures eg thumbs/toes

46
Q

Which experiment proves the role of the ZPA and Shh in craniocaudal limb development?

A

Transplantation of the ZPA induces mirror image polydactyl

ie. put an extra ZPA in the cranial region you get little fingers both cranially and caudally

47
Q

In which week do the terminal regions of the limb buds flatten to form hand and foot plates?

A

Week 6

48
Q

From the flattened hand and foot plates how are the fingers formed?

A

Formed by apoptosis
This apoptosis splits the AER into 5 parts which continue to grow and form fingers
Apoptosis continues in the intervening tissues between digits

49
Q

What is amelia and how does it occur?

A

Complete absence of one or more limbs

early loss of Fgf signalling

50
Q

What is meromelia and how does it occur?

A

Partial absence of a limb

later or partial loss of Fgf signalling

51
Q

What is phocomelia and how does it occur?

A

Digits develop prematurely
Proximal elements of the limbs are absent aka. flipper limb
Can be due to genetic factors or teratogens eg. Thalidomide which inhibits Fgf 10 and Fgf 8 expression

52
Q

Thalidomide inhibits the expression of which growth factors?

A

Fgf 10 and Fgf 8

53
Q

Why is phocomelia due to thalidomide still seen in Brasil?

A

Thalidomide is used to treat leprosy and HIV and there is often a lack of education for mothers regarding the danger to babies

54
Q

What is syndactyly and what is it caused by?

A

Fused digits

Failure of apoptosis

55
Q

What is polydactyly and what is it caused by?

A

Extra digits

Inappropriate or ectopic Shh expression

56
Q

What is ectrodactyly and what is it caused by?

A

Split hand or foot
Aka lobster claw deformity
Failure of the middle AER to form properly - still forms either side of the middle so end up with a split hand or foot

Year 2 Term 1 Movement (8 decks)

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