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MSK > 1 - embryology of limbs > Flashcards

1 - embryology of limbs Flashcards

1
Q

when does limb development start?

A

begins near the end of 4th week

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2
Q

how is limb development initiated?

A

Activation of mesenchymal cells in the somatic lateral mesoderm

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3
Q

what genes regulate patterning during limb development?

A

homeobox genes

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4
Q

when does upper limb bud appear?

A

day 24

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5
Q

when does lower limb bud appear?

A

day 25/26

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6
Q

what HOX genes are expressed in upper limb?

A

HOXd 9-13

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7
Q

removal of which 2 HOX genes results in radius and ulna not forming?

A

HOXa and HOXd

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8
Q

how do limb buds elongate?

A

by the proliferation of the mesenchyme

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9
Q

where do upper limb buds develop?

A

opposite the lumbar and sacral segments

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10
Q

how is the apical ectodermal ridge (AER) formed?

A

the ectoderm at the apex of each bud thickens

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11
Q

what is the AER made of?

A

it is a multilayered epithelial structure

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12
Q

what does the AER influence?

A

it exerts an inductive influence on the limb mesenchyme

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13
Q

what cells are present in the mesenchyme adjacent to the AER?

A

undifferentiated, rapidly proliferating cells

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14
Q

what cells are present in the mesenchyme proximal to the AER?

A

they differentiate into blood vessels and cartilage bone models

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15
Q

what develops into hand and foot plates?

A

the distal ends of the limb buds

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16
Q

what has occurred by the end of week 6?

A

mesenchymal tissue in hand plates has condensed to form digital rays

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17
Q

what occurs in week 7?

A

digital rays are formed in the foot plates

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18
Q

what is mediated by bone morphogenetic proteins?

A

apoptosis (which accounts for the breakdown in interdigital regions)

19
Q

when do the Cartilaginous precursors of the limb bones develop by chondrification within the mesoderm?

A

week 6

20
Q

what appears in weeks 8-12 in response to growth factors?

A

1y centres of ossification

21
Q

what type of ossification is present in all limb bones (except clavicle)?

A

endochondrial ossification

22
Q

what type of ossification is present in clavicle?

A

membranous

23
Q

how do upper limbs rotate?

A

90 degrees laterally

24
Q

how do lower limbs rotate?

A

90 degrees medially

25
Q

when do peripheral nerves grow and where do they originate?

A

week 5 - originate from the developing limb plexus into the mesenchyme of the limbs

26
Q

term for total absence of limbs at birth?

A

amelia

27
Q

term for partial absence of limbs at birth?

A

meromelia

28
Q

term for some long bone absence at birth?

A

phocomelia

29
Q

term for only small parts absent at birth?

A

micromelia

30
Q

how is lobster claw foot inherited?

A

autosomal dominant

31
Q

when is the critical period of limb development?

A

24-36 days after fertilisation

32
Q

polydactyly?

A

presence or more than 5 digits on hand/ foot

33
Q

what 2 mechanisms lead to polydactyly?

A

inherited or teratogen induced

34
Q

what is syndactyly?

A

webbing/fusions of bones

35
Q

cutaneous syndactyly?

A

simple webbing between the digits

36
Q

osseous syndactyly?

A

fusion of bones

37
Q

when does osseous syndactyly occur?

A

when notches between digital rays fail to develop

38
Q

what does thalidomide cause?

A

absence/ deformity of long bones - meromelia

39
Q

side effects of thalidomide?

A

intestinal atresia, cardiac anomalies

40
Q

what is congenital clubfoot AKA?

A

talipes equinovarus

41
Q

what is congenital clubfoot?

A

sole of foot is turned medially and the foot is inverted

42
Q

2 causes of clubfoot?

A

1 - multifactorial (genetics and environment), 2 - abnormal positioning of foetus’ lower limb in utero

43
Q

2 causes of developmental dysplasia of the hip?

A

1 - abnormal development of acetabulum, 2 - generalised joint laxity

44
Q

does syndactyly occur more in hand/foot?

A

in feet more often

MSK (26 decks)

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