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MSK 1!!! > Limb Development > Flashcards

Limb Development Flashcards

1
Q

Why are limbs important?

A

To break it down in da club after QUARANTINE!

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2
Q

When do upper and lower limb buds form?

A

4th week
Upper - 24 days
Lower- 25-26 days

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3
Q

What is the apical ectodermal ridge (AER)?

What happens there?

A

A thick band of ectoderm where limb buds form.

Mesenchyme proliferate and grow from ateral plate mesoderm (limb buds now bulge)

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4
Q

Regions of limb outgrowth

A

Stylopod- humerus or femur
Zeugopod- radius and ulna; tibia and fibula
Autopod- hands/ feet

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5
Q

Axes of limb bud?

A

Proximal-Distal (Shoulder-Digits) FGF signalling & HOX
Cranial-Caudal (Hallu- Phalanx V) SHH & HOX
Dorsal-Ventral (Dorsum-Palm) Wnt7a and Engrailed (En1)

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6
Q

What growth factor induces AER?

A

FGF10

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7
Q

What does AER secrete?

A

FGF8 (bc positive feedback from FGF10)

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8
Q

FGF and AER make what axis?

A

Proximodistal

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9
Q

Manipulating AER (early, late, and transplant)

A

Early removal: only 1st segment
Late removal: 1st and 2nd segments
Transplanting: supernumerary digits

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10
Q

Meromelia

A

‘partial-limb’

intermediate to late loss of FGF

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11
Q

Amelia

A

‘no-limb’

early loss of FGF signaling

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12
Q

Phocomelia

A

‘seal’s-limb’ loss of long bones
Partial loss of FGF signalling
OR thalomide disrupting HOX

**thalomide used to be taken during pregnancy

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13
Q

Adactyly

A

Absent digits

Late loss of FGF

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14
Q

Ectrodactyly

A

Split hand. ‘Lobster claw’
Partial absense of FGF8 from AER
1.5:100,000
(EEC)- ectrodactly- ectodermal dysplasia, cleft palate

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15
Q

Zone of Polarizing Activity (ZPA) makes ___ axis?

By expressing what?

A

craniocaudal

SHH

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16
Q

What digit is most likely to form in absence of SHH?

A

Digit 1 (cranial end)

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17
Q

How does Polydactyly occur?

A

Overexpression of SHH causes 2nd ZPA to form (now in cranial and caudal end)
Extra digits lack normal musculature

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18
Q

HOX genes regulate what axes?

A

craniocaudal & proximodistal

19
Q

HOX9-10 paralogs

A

specifies stylopod (HOX9=scapula)

20
Q

HOX11 paralogs

A

specifies zeugopod

HOX 9-11

21
Q

HOX12-13 paralogs

A

specifies autopod

HOX9-13

22
Q

Brachydactyly and its genetics?

A 
shortening of fingers and toes 
Genetic change in HOXD13 (finger gene)
OR PTHLH (parathyroid hormone like hormone)
Autosomal dominant
23
Q

What regulates dorsal ventral Axis?

A

Wnt7a: expressed in dorsal ectoderm
Engrailed (En1): expressed in ventral ectoderm.
- Prevents Wnt7a. restricts positioning of AER to establish dorsoventral

24
Q

What signals digit formation?

A

High BMP = High cell death of cutaneous webbing

25
Q

When do digital rays form in hand plates?

A

by 6th week
day 41
limb is cartilagenous

26
Q

When do digital rays form in foot plates?

A

by 7th week
day 46
osteogenesis begins

27
Q

When do separate digits form?

A

by 8th week

upper: day 52
lowwer: day 56

28
Q

What is syndactyly?

A

fused digits because digital rays failed to develop

29
Q

What is cutaneous syndactyly?

A

webbing present because low BMP

30
Q

What is osseous syndactyly?

A

Synostosis (bone fusion)
Failure to form interdigit notch
HOXD13 (finger gene)
Auto dominent

31
Q

What does the dorsal limb muscle mass form?

A

Upper: extensor and suppinators
Lower: extensor and abductors

32
Q

What does the ventral limb muscle mass form?

A

Upper: Flexors and pronators
Lower: Flexors and adductors

33
Q

Where do limb tendons arise from?

A

Lateral plate mesoderm

vertebral tendons from paraxial

34
Q

When does limb innervation begin?

A

5th week

Motor neurons innervate 1st, then sensory

35
Q

What innervates the limb’s dorsal muscle mass?

A

dorsal branches of ventral rami (these are not epaxial)

36
Q

What innervates the limb’s ventral muscle mass?

A

ventral branches of ventral rami

37
Q

Dorsal aorta gives rise to ______ which give rise to ______

A

intersegmental arteries

primary axial arteries and its branches

38
Q

Describe vascular development path of upper limb

A

Primary Axial a. –> brachial a. & common interosseous a. –> ulnar & radial a.

39
Q

Describe vascular development path of lower limb

A

Primary Axial a. –> deep artery of thigh –> anterior & posterior tibial a.

40
Q

When do limb buds rotate? What limbs are doing what?

Osteogenesis also begins at this time

A

Week 7
Upper: 90 laterally
Lower: 90 medially

41
Q

What can amniotic bands do?

A

When there is too little amniotic fluid, amniotic bands stick to fetal structure and cut off growth.

42
Q

What is bilateral talipes equinovarus

A

‘Club foot’
oligohydramnios reduces fetal movement
too litlle amniotic fluid compresses fetus hindering outward rotation of limbs
1:1000

43
Q

When does primary ossification begin?

A

Week 12.

this isn’t osteogenesis

MSK 1!!! (10 decks)

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