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SHB > 9.21.16 Limb Development > Flashcards

9.21.16 Limb Development Flashcards

1
Q

___ appear toward the end of the 4th week as slight bulges of the ventrolateral body wall.

A

Limb buds

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2
Q

Most of the initial growth of the limbs occurs during weeks ___.

A

4-8

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3
Q

The upper limb buds develop approximately ___ days before the lower limb buds.

A

2

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4
Q

The tissues of the limb buds are derived from what two main sources?

A

Mesoderm and ectoderm

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5
Q

What is the AER?

A

Apical ectodermal ridge

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6
Q

What does the AER do?

A

Exerts an inductive influence on the limb mesenchyme, promoting growth and development of the limbs.

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7
Q

How do limb buds elongate?

A

By proliferation of the mesenchyme within them

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8
Q

Limb elements arise from what three things?

A
  1. Paraxial mesoderm (somites): dermatome (dermis) and myotome (limb muscles)
  2. Lateral plate mesoderm (bones and blood vessels)
  3. Neural crest cells (Schwann cells and melanocytes)
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9
Q

What is the first step of limb patterning?

A

Four paddle-like limb buds develop from the ventrolateral body wall

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10
Q

What is the second step of limb patterning?

A

A circular groove appears, separating a hand plate from the upper limb bud and a foot plate from the lower one.

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11
Q

During the third step of limb patterning, a mesodermal condensation in the hand and foot plates results in the appearance of ___.

A

Digital rays

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12
Q

During the four step of limb patterning, a thin membrane intervening the rays (webs) breaks down and the digits become separated by ___.

A

Notches

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13
Q

Finally, a second circular constriction divides each limb imto three segments. What are these?

A

Upper limb: arm, forearm, hand

Lower limb: thigh, leg, foot

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14
Q

The four limb buds are extended at a ___ angle to the trunk.

A

Right

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15
Q

What three axes do the limbs grow in?

A

Proximal-distal, anterior-posterior, dorsal-ventral

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16
Q

What are the 2 borders and 2 surfaces of each limb?

A

Borders: preaxial (cephalic) near the big digit and postaxial (caudal)
Surfaces: ventral (flexor) and dorsal (extensor)

17
Q

During the fifth week, peripheral nerves grow from the developing ___ into the mesenchyme of the limbs.

A

Limb plexuses

18
Q

What are the two limb plexuses?

A

Brachial and lumbosacral

19
Q

Limb outgrowth initiated by the AER at the tip of the limb buds proceeds from ___ to ___.

A

Proximal (shoulder or hip); distal (hand or foot)

20
Q

The proximo-distal growth and patterning is dependent on ___ signaling from the AER.

A

FGF

21
Q

Anything that disrupts FGF signaling and/or formation and maintenance of the AER will result in ___.

A

Arrested limb development

22
Q

Proximo-distal patterning of the limb elements is also dependent on ___ genes to specify each of the elements. Disruption of these genes will result in loss of specific limb elements.

A

HOX

23
Q

Describe the limb rotation of the upper limb during weeks 6-8.

A

90 degrees laterally:

  1. Flexors (anterior) and extensors (posterior)
  2. Radius (lateral) and ulna (medial)
  3. Thumb (lateral) and elbow joint points backward
24
Q

Describe the limb rotation of the lower limb during weeks 6-8.

A

90 degrees medially:

  1. Flexors (posterior) and extensors (anterior)
  2. Fibula (lateral) and tibia (medial)
  3. Big toe (medial) and knee joint points forward
25
Q

There is a strong relationship between the growth and rotation of the limbs and the ___ of the limbs.

A

Cutaneous segmental nerve supply

26
Q

What is the area of skin supplied by a single spinal nerve and its spinal ganglion?

A

Dermatome

27
Q

What is the area of skin supplied by a peripheral nerve?

A

Cutaneous nerve area

28
Q

True or false - dermatomes and cutaneous nerve areas show considerable overlapping.

A

True

29
Q

What is absence of an entire limb?

A

Amelia

30
Q

What is absence of part of a limb?

A

Meromelia

31
Q

What is a short, poorly formed limb?

A

Phocomelia

32
Q

What is an extra digit?

A

Polydactyly

33
Q

What is fusion of digits?

A

Syndactyly

34
Q

What is it called when the middle digit is absent?

A

Lobster claw deformity

SHB (36 decks)

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