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MSK > 1. Limb development > Flashcards

1. Limb development Flashcards

1
Q

When does limb development begin?

A

End of 4th week

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2
Q

Upper limb development precedes lower limb development by how many days?

A

2

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3
Q

What is the structure of a limb bud?

A

Mesenchymal core with ectoderm covering.

Thickened ectoderm at distal tip forming AER.

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4
Q

Which cells are responsible for the elongation of the limb?

A

Proliferating mesenchyme core

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5
Q

Where is the zone of polarising activity?

A

Posterior base of limb bud

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6
Q

What is the function of the ZPA?

A
  • Maintains the AER

- controls anterior-posterior axis development

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7
Q

What are the 3 spatial axis of limb development and what is responsible for each of their development ?

A
  1. Anterior-posterior - ZPA
  2. Dorsal - ventral - Ectoderm
  3. Proximal-distal - AER
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8
Q

Which cells are critical for limb outgrowth?

A

Apical Ectodermal Ridge

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9
Q

What is the function of the apical ectodermal ridge (AER)?

A

Stimulates outgrowth of limb and maintains undifferentiated state in
mesenchyme immediately underlying it.

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10
Q

What are digital rays?

A
  • mesenchyme condensations within the hand/foot plates.

- cartilaginous models of the digital bones

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11
Q

Explain how the digits are sculpted.

A

AER remains on tips of digital rays but regresses in between digits. Apoptosis of the tissues between digits without AER.

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12
Q

What is syndactyly?

A

Fusion of digits

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13
Q

What are the 2 categories of syndactyly?

A

Cutaneous - connective tissue fusion only

Osseous - bone fusion

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14
Q

What is polydactyly and what is its inheritance pattern?

A

Extra digits

Recessive

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15
Q

How does amelia differ from meromelia?

A

Amelia - complete absence of a limb or limbs

Meromelia -partial absence of a limb or limbs

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16
Q

Does the upper limb rotate medially or laterally during development?

A

laterally (thumb is lateral)

17
Q

Does the lower limb rotate medially or laterally during development?

A

Medially (big toe is medial)

18
Q

Describe the position of the upper limb before and after rotation.

A

Before - thumbs up, elbows out

After- thumbs out, elbow down

19
Q

Describe the position of the lower limb before and after rotation.

A

Before - soles of feet facing each other, knees out

After- soles down, knees up

20
Q

What is the structural defect underlying congenital dislocation of the hip (CHD)?

A

Underdevelopment of acetabulum and head of femur

21
Q

Explain what happens if the AER is disrupted.

A

No limb growth/shortened limbs.

22
Q

CHD is associated with the breech position, why is this?

A

Breech presentation may place undue pressure on the developing hip joint: fails to complete normal development.

MSK (16 decks)

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