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MSK > Embyrology > Flashcards

Embyrology Flashcards

1
Q

When does limb bud development begin and with what?

A

4th week with the activation of mesenchymal cells in the somatic lateral mesoderm

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2
Q

What is embyrological patterning?

A

Grouping of cells together in the proper relationship to each other and the tissue surrounding them

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3
Q

What genes control embryological patterning of the limbs?

A

Homeobox genes

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4
Q

At what days do the limb buds appear?

A

Day 24 - upper limb bud appears

Day 25-26 - lower limb bud appears

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5
Q

What do HOX genes do?

A

Control the body plan of an embryo from head to toe

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6
Q

Where are HOX genes expressed?

A

Regionally in limbs

They determine which skeletal element is formed

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7
Q

HOX expression results from combination of expression of what 3 other things?

A

SHH, FGFs, WNT-7a

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8
Q

What type of HOX is expressed in the upper limb?

A

HOX 9-13

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9
Q

Removal of what two HOX genes will lead to the radius and ulna not forming?

A

HOXa11, HOXd11

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10
Q

How do limb buds elongate?

A

By proliferation of mesenchyme (embryonic connective tissue)

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11
Q

Where do the upper limb and lower limb buds develop?

A

Upper limb - opposite caudal cervical segments

Lower limb - opposite lumbar and sacral segments

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12
Q

What forms at the apex of each limb bud?

A

Apical ectodermal ridge (AER)

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13
Q

What are the AER?

A

Multi-layered epithelial structure that is restricted to the end of limb bud

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14
Q

What do the AERs do?

A

Exert an inductive influence on limb mesenchyme

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15
Q

What lies adjacent to the AER?

A

Undifferentiated, rapidly proliferating cells

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16
Q

What lies proximal to the AER?

A

Mesenchymal cells which differentiate into Bas and cartilage bone models

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17
Q

What develops at the end of the limb buds?

A

Flattened hand plates/foot plates

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18
Q

By the end of the 6th week, what happens in the hand plates?

A

Mesenchymal tissue condenses to form digital rays

19
Q

By the end of the 7th week, what happens in the foot plates?

A

Digital rays form

20
Q

What prevents webbed fingers/toes occurring?

A

Programmed cell death responsible for tissue breakdown in interdigital regions

21
Q

What mediates the apoptosis in the interdigital regions?

A

Bone morphogenic proteins

22
Q

Describe the process of bone ossification in the limbs

A

Cartilaginous precursors develop by chondrofication within mesoderm in the 6th week
Primary centres of ossification appear in wks 8-12 in response to growth factors

(SO all endochondral ossification apart from clavicle)

23
Q

Distinguish between endochondral and intramembranous ossification

A

Endochondral - cartilage precursor model laid down first (happens in long bones)
Intramembraneous - bone laid down directly into mesenchyme, occurs in flat bones

24
Q

Define ossification

A

The process of laying new bone down by osteoblasts

25
Q

During limb rotation, in which direction do the limb buds rotate?

A

Upper limb - 90 degrees laterally

Lower limb - 90 degrees medially

26
Q

What happens, in relation to nerve development in the limb in the 5th week?

A

In the 5th week, peripheral nerves grow developing limb plexuses (brachial/lumbosacral) into the mesenchyme of the limbs

27
Q

Define amelia

A

Total absence of limbs

28
Q

Define meromelia

A

Partial absence of limbs

29
Q

Define phocomelia

A

Some long bone absence, e.g. radius/fibula

30
Q

Define micromelia

A

All parts present ut small

31
Q

What is lobster claw foot?

A

Splitting of the footplate

Can be inherited as an autosomal dominant trait

32
Q

What is the critical period for limb development?

A

24-36 days after fertilisation

33
Q

Define polydactyly

A

Presence of more than 5 digits on the hands/feet

Extra digit incompletely formed and lacks muscular development

34
Q

What may cause polydactyly?

A

Alcohol, thalidomide, inherited traits

35
Q

Define syndactyly

A

Webbing of hands/feet
Common birth detect
More common in feet as opposed to hands

36
Q

Define cutaneous syndactyly

A

Simple webbing between digits

37
Q

Define osseous syndactyly

A

Fusion of bones, notches between digital rays fail to develop

38
Q

What can thalidomide use in early pregnancy lead to?

A

Amelia/meromelia, intestinal atresia, cardiac abnormalities

39
Q

What is the other name for congenital clubfoot?

A

Tapiles equinovarus

40
Q

What is club foot?

A

Sole of foot turned medially and foot inverted

41
Q

What causes club foot?

A

Multifactorial - genetic and environmental factors

?Abnormal positioning/restricted movement of foetus’s lower limb in utero

42
Q

What may cause abnormal development of the hip?

A

Common after breech deliveries - ?breech posture during late pregnancy (abnormal development of acetabulum and head of femur)

General joint laxity may be attributed to many factors and is associated with congenital dislocation of the hip

43
Q

When is the sensitive period of thalidomide use?

A

4-8 weeks

44
Q

Why does thalidomide lead to the problems previously mentioned?

A

It disrupts cell adhesion and angiogenesis in the embryo

MSK (27 decks)

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