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Movement > Embryology > Flashcards

Embryology Flashcards

1
Q

When does limb development occur?

A

Weeks 4-8

First appear at week 4

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2
Q

Where do the limb buds appear initially?

A

Venterolateral wall (outpouchings)

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3
Q

Which limbs develop first?

A

Upper limbs (few days)

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4
Q

Which 2 germ layers contribute to limb development?

A
  • Ectoderm

- Mesoderm

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5
Q

Where is the initial core tissue from?

A

Lat plate mesoderm (covered by ectoderm)

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6
Q

What does the lateral plate mesoderm differentiate into?

A

Condenses to mesenchyme, which forms bones and connective tissue.

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7
Q

Which part of the mesoderm is the skeletal muscle of the limbs derived from?

A

Paraxial mesoderm

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8
Q

What does paraxial mesoderm divide into, and where does this take place?

A

Somites, either side of neural tube

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9
Q

Which 2 parts do the somites divide into?

A

Ventral and dorsolateral

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10
Q

What is the ventral part called and what does it form?

A

Sclerotome, and forms vertebral collumn

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11
Q

What is the dorsolateral part called and what does it form?

A

Dermomyotome, which divides into dermatome (dermis of skin) and myotome (skeletal muscle)

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12
Q

What does the myotome differentiate into?

A
  • Dorsal epimere

- Ventral hypomere

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13
Q

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

A

Back muscles, which are innervated by dorsal rami of spinal nerves

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14
Q

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

A

Muscles of thorax, abdomen and limbs, which are innervated by ventral rami of spinal nerve

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15
Q

When does the myotome differentiate into the epimere and hypomere?

A

5 weeks

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16
Q

Which part of the myotome forms the limb muscles?

A

Ventral hypomere

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17
Q

At which vertebral level does upper limb skeletal muscles develop from hypomere?

A

C5-C8

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18
Q

At which vertebral level does lower limb skeletal muscles develop from hypomere?

A

L3-L5

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19
Q

What do hypomeres divide into in the limbs? When does this occur?

A

Posterior and anterior condensations

-7 weeks

20
Q

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

A

Posterior - Extensors and supinators

Anterior - Flexors and pronators

21
Q

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

A

Posterior - Extensors and abductors

Anterior - Flexors and adductors

22
Q

What innervates the lower limb?

A

Lumbosacral plexus (L4-S3)

23
Q

When does limb rotation occur?

A

6th-8th week

24
Q

Which way does the upper limb rotate?

A

90* laterally

flexors ant

25
Q

Which way does the lower limb rotate?

A

90* medially

flexors post

26
Q

What are the 3 axes of limb rotation?

A
  • PROXIMODISTAL (outwards eg shoulder >hand)
  • CRANIOCAUDAL (eg thumb > most cranial)
  • DORSOVENTRAL (palm is ventral, knuckles are dorsal)
27
Q

What growth factor is secreted by the lateral plate mesoderm?

A

Fibroblastic growth factor 10 (Fgf 10)

28
Q

What does Fgf 10 cause?

A

Thickens overlying ectoderm at tip to form apical ectodermal ridge (AER)

29
Q

What does the AER secrete?

A

Fgf 4 & 8

NB. excess implanted into embryo > extra limbs

30
Q

What do Fgf 4 & 8 cause?

A

Rapid proliferation of mesenchymal cells underlying the AER - PROGRESS ZONE (maintains proximodistal outgrowth).

31
Q

3 growth factors involved in proximodistal outgrowth

A 
Fgf 10 (lat plate mesoderm)
Fgf 4 (AER)
Fgf 8 (AER)
32
Q

How is dorsoventral patterning controlled?

A

Dorsal ectoderm expressed Wnt7 –> nails.

Ventral ectoderm expresses Engrailed 1 –> Wnt 7 inhibition and palm devlopment

33
Q

What does Wnt 7 expression lead to?

A

Nail formation

34
Q

What does Engrailed 1 expression lead to?

A

Wnt 7 inhibition and palm formation

35
Q

Which region of the mesenchyme controls craniocaudal development?

A

Zone of polarising activity (ZPA).

36
Q

What protein is expressed by ZPA?

A

Sonic hedgehog (Shh)

37
Q

How does Shh control limb development?

A

Shh diffuses in the cranial direction, so concentraion decreases (^ conc caudally).
High concentrations induce formation of caudal structures (eg little finger)

38
Q

When do terminal limb regions flatten to form hand/foot plates?

A

Week 6

39
Q

How are fingers/toes formed from flattened plates?

A

Apoptosis - splits AER into 5 parts.

40
Q

What is amelia and what causes it?

A

Complete absence of one or more limbs

-early loss of Fgf signalling

41
Q

What is meromelia and what causes it?

A

Partial absence of a limb later

-partial loss of Fgf signalling

42
Q

What is phocomelia and what causes it?

A

Proximal elements of the limbs are absent; normal digits, shortened limbs.
-genetic factors,teratogens (eg. thalidomide)

43
Q

How does thalidomide lead to shortened limbs?

A

Inhibits Fgf 10 and Fgf 8

44
Q

What is syndactyl and what causes it?

A

Fused digits

-apoptosis failure

45
Q

What is polydactyl and what causes it?

A

Extra digits

-inappropriate Shh expression

46
Q

What is ectrodactyl and what causes it?

A

Split hand/foot

-failure of middle AER to form properly

Movement (12 decks)

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