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MSK I > Development of Limbs > Flashcards

Development of Limbs Flashcards

1
Q

when do limb buds begin to appear

A

week 4

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2
Q

when do digits begin to appear

A

week 8

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3
Q

when does the 1st ossification occur

A

week 12

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4
Q

which limbs develop first: upper or lower

- why

A

upper

- blood is being pumped to the head for development; upper limb is closer to head

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5
Q

how does development of the limbs proceed

A

proximodistally

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6
Q

where does the muscle of the limbs originate from

A

paraxial mesoderm –> somite –> myotome –> hypomere –> hypaxial muscles

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7
Q

where do the cartilage and connective tissue of the limbs originate from

A

somatic layer of the lateral plate

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8
Q

what does the limb forming mesoderm release to stimulate the surface ectoderm to become to the apical ectodermal ridge

A

FGF-10

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9
Q

what does FGF-10 do

A

stimulates surface ectoderm to become the apical ectodermal ridge

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10
Q

what is the apical ectodermal ridge and what is it needed for

A
  • thickening of the surface ectoderm

- needed for limb development

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11
Q

what does the apical ectodermal ridge release to stimulate limb mesoderm

A

FGF-8 and FGF-4

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12
Q

what does the release of FGF-8 and FGF-4 from the apical ectodermal ridge do

A

stimulates limb mesoderm which then proliferates and migrates to facilitate proximodistal development of the limbs

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13
Q

what is the most proximal region of the limb buds and what does it develop into in the upper limb

A

Stylopod region

- humerus, femur

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14
Q

what is the middle region of the limb buds and what does it develop into in the upper limb

A

Zeugopod

- radius/ulna and tibia/fibula

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15
Q

what is the most distal region of the limb buds and what does it develop into in the upper limb

A

Autopod

- carpals, metacarpals, digits, tarsals, metatarsals

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16
Q

when do the hand and foot plates develop as well as the chondrification centers

A

week 5

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17
Q

when do the digital rays of hands develop

A

week 6

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18
Q

what condenses to make bones for the digits in week 6

A

somatic lateral plate

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19
Q

at week 6 what is the entire limb skeleton made of

A

cartilage

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20
Q

when do the digital rays of the feet, rotation of the limbs, and osteogenesis of long bones begin

A

week 7

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21
Q

which develops first: hand plates or foot plates?

A

hand plates

22
Q

when does separation of digits and apoptosis occur?

A

week 8

23
Q

what is apoptosis due to in week 8

A

BMP

24
Q

when do motor axons from the spinal cord enter the limb buds

A

week 5

25
Q

Name the specific myotomes for where:

  • the upper limbs develop
  • the lower limbs develop
A

upper limbs: cervical myotomes

lower limbs: lumbar and sacral myotomes

26
Q

what rotations occur in the limbs at week 7

- where do the elbows and knees now point

A

upper limbs rotate 90 degrees laterally
lower limbs rotate 90 degrees medially
- the elbows now point caudally and the knees point cranially

27
Q

what artery does the primary axial artery become in the upper limbs

A

brachial artery

28
Q

what artery does the primary axial artery become in the lower limbs

A

deep artery of the thigh

29
Q

what occurs to remodel arterial supply in the limbs

A

angiogenesis

30
Q

Club Foot (talipes Equinovarus)

A
  • sole of foot is turned medially and inverted
  • all anatomical structures are present
  • 2x more frequent in males
31
Q

Potential causes of Club Foot

A

not enough amniotic fluid so limbs cannot rotate properly

32
Q

Developmental Hip Displasia

A
  • underdevelopment of acetabulum in the hip bone (hip joint socket)
33
Q

what do Hox genes regulate in limb development

A
  • positioning of the limbs along the craniocaudal axis in proximo-distal growth
  • regulate types and shapes of bones
34
Q

what do things are needed for proximo-distal patterning

A

Apical ectodermal ridge (AER)

HOX genes

35
Q

what maintains the dorsal surface in dorso-ventral patterning

A

Wnt7

36
Q

what maintains the ventral surface in dorso-ventral patterning

A

BMPs

37
Q

what do Wnt7 and BMP set up in patterning growth

A

the apical ectodermal ridge (AER)

38
Q

what establishes the anterior-posterior patterning

A

Zone of Polarizing Activity (ZPA)

39
Q

how does ZPA signal posterior elements

- what are the posterior elements

A

SHH and retinoic acid signaling

- digits 3-5 and ulna

40
Q

loss of ZPA results in

A

loss of posterior elements

- ex: 4th digit, 5th digit, ulna

41
Q

up-regulation of ZPA results in

A

additional posterior elements

- ex: polydactyly

42
Q

duplication of ZPA results in

A

duplication of posterior elements

  • ex: little fingers on both sides of the thumb
  • ex: second set of toes
43
Q

why can disruption of AP patterning and growth result in loss of anterior elements

A

posterior elements are formed prior to anterior elements

44
Q

Meromelia

- when does the defect occur

A

results in a shrunken and deformed extremity

- defect occurs in weeks 3-5 in development

45
Q

Phocomilia

A

shortened hands and legs

46
Q

what prescribed drug used to cause meromelia

A

Thalidomide

47
Q

brachydactyly

  • how is it caused
  • when
A

shortened digits

- FGF-8, 10, and 4 disruption in weeks 6-8

48
Q

syndactyly

  • how is it caused
  • when
A

webbing of the digits

- down-regulation of BMPs needed for apoptosis in week 8

49
Q

Amelia

  • what is it
  • when
A

missing both upper limbs

- weeks 3 and 4

50
Q

Ectrodactyly - “Lobster Claw”

  • what causes it
  • when
A

apical ectodermal ridge was down-regulated and the digits did not form
- week 6 for hand and week 7 for feet

51
Q

Arthrogryposis

A

congenital joint contractures

- causes unclear

MSK I (15 decks)

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