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Systems: MSK AB > Embryology > Flashcards

Embryology Flashcards

1
Q

When does limb development occur?

A

Begins near the end of the 4th week

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2
Q

When do the upper limb buds appear?

A

Day 24

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3
Q

When do the lower limb buds appear?

A

Day 25/26

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4
Q

What causes the start of limb bud development?

A

Activation of mesenchymal cells in the somatic lateral mesoderm

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5
Q

What is responsible for proximo-distal patterning?

A

HOX genes

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6
Q

What do HOX genes do?

A

-They are regionally expressed in limbs and determine which skeletal element is formed

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7
Q

What does HOX gene expression result from?

A

A combination of the expression of SHH, FGFs and WNT7a

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8
Q

What HOX genes have expression in the upper limb?

A

9-13

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9
Q

What happens if you remove HOXa 11 and HOXd 11?

A

radius and ulna do not form

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10
Q

How do limb buds elongate?

A

By proliferation of mesenchyme

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11
Q

What do upper limb buds form opposite?

A

The caudal cervical segments

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12
Q

What do lower limb buds form opposite?

A

The lumbar and sacral segments

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13
Q

What happens at the apex of each limb bud?

A

The ectoderm thickens to form an apical ectodermal ridge (AER)

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14
Q

Where is AER restricted to?

A

End of limb bud

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15
Q

What is the structure of AER?

A

Multi-layered epithelial structure

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16
Q

What impact does AER have on the limb mesenchyme?

A

Exerts an inductive influence

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17
Q

What does the mesenchyme adjacent to the AER consist of?

A

Undifferentiated rapidly proliferating cells

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18
Q

What happens to mesenchymal cells proximal to the AER?

A

Differentiate into blood vessels and cartilage bone models

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19
Q

What happens to the distal ends of the limb buds?

A

Flatten into paddle-like hand plates and flipper-like foot plates

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20
Q

What should have happened by the end of the 6th week?

A

Mesenchymal tissue in hand plates should have condensed to form digital rays

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21
Q

What happens during the 7th week?

A

Digital rays are formed in the foot plates

22
Q

What is responsible for the tissue breakdown in the interdigital regions?

A

Programmed cell death (apoptosis)

23
Q

What is the apoptosis of the interdigital regions mediated by?

A

Bone morphogenetic proteins

24
Q

What happens to cartilaginous precursors in the mesoderm during the 6th week?

A

They develop by chondrification

25
Q

When do primary ossification centres appear?

A

Weeks 8-12 in response to growth factors

26
Q

What is the only limb bone that does not undergo endochondrial ossification?

A

Clavicle (membranous)

27
Q

Describe the limb rotation which takes place.

A
  • Upper limbs and lower limbs rotate
  • Upper limbs rotate 90 degrees laterally so that extensors are on the lateral and posterior surfaces (and the thumb is lateral)
  • Lower limbs rotate 90 degrees medially so that the extensors are on the anterior surface (and the big toe is medial)
28
Q

How are dermatomal patterns established?

A

During the 5th week, peripheral nerves grow from the developing limb plexus
(brachial and lumbosacral) into the mesenchyme of the limbs

29
Q

What are limb defects often associated with?

A

Other defects either hereditary or teratogen caused

30
Q

Amelia

A

Total absence of a limb

31
Q

Meromelia

A

Partial absence of a limb

32
Q

Phocomelia

A

Some long bones absent

33
Q

Micromelia

A

All parts present but small

34
Q

What is the critical period of limb development?

A

24-36 days

35
Q

How can lobster claw foot be inherited?

A

Autosomal dominant trait

36
Q

Polydactyly

A
  • Presence of more than 5 digits on the hands and feet

- Extra digits are incompletely formed and lack muscular development

37
Q

How can polydactyly occur

A

May be inherited or teratogen induced

38
Q

Syndactyly

A
  • Common birth defect of the hand or foot

- Occurs more frequent in the foot than hand

39
Q

Cutaneous syndactyly

A

Simple webbing between the digits

40
Q

Osseous syndactyly

A

Fusion of bones which occurs when notches between digital rays fail to develop

41
Q

What is thalidomide?

A

-A drug used as a sleeping tablet and anti-nausea between 1957 and 1962

42
Q

What did thalidomide use result in?

A

-Absence or deformity of long bones (intestinal atresia and cardiac abnormalities

43
Q

What is the sensitive period for thalidomide?

A

4-8 weeks

44
Q

How does thalidomide work?

A

Acts by disrupting cell adhesion and angiogenesis

45
Q

What is thalidomide now used for?

A
  • Cancer
  • Leprosy
  • AIDs
46
Q

What is another name for congenital clubfoot?

A

Talipes equinovarus

47
Q

How does club foot present?

A
  • Relatively common

- Sole of foot is turned medially and the foot is inverted

48
Q

What is the cause of clubfoot?

A
  • Multifactorial (genetic and environmental factors)

- Abnormal positioning or restricted movement of the foetus’s lower limb in the utero (evidence is inconclusive)

49
Q

What are the 2 components of hip dysplasia?

A
  • Abnormal development of the acetabulum

- Generalised joint laxity

50
Q

What causes abnormal development of the acetabulum?

A
  • Common after breech births

- Breech posture during late pregnancy (abnormal development o f acetabulum and head of femur)

51
Q

What causes generalised joint laxity?

A
  • Multifactorial

- Associated with congenital dislocation of the hip

Systems: MSK AB (43 decks)

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