Lecture 19: Limb Development Flashcards

1
Q

Which develops first? Lower limbs or upper limbs?

A

Upper Limbs develop first

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2
Q

In what week do the upper and lower limbs begin to develop?

A

Week 4

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3
Q

Why do the upper limbs develop slightly ahead?

A

Better blood supply due to the fact that the embryo favors supplying the brain - and therefore the upper half of the embryo - with blood.

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4
Q

When do the limb buds develop?

A

4th Week

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5
Q

What embryological structure gives rise to the muscle of the limbs?

A

The Hypomere (Pariaxial Mesoderm -> Somite -> Myotome -> Hypomere)

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6
Q

Where does the cartilage and connective tissue of the upper limb come from embryologically?

What does cartilage serve as a precursor for in the upper limb?

A

Somatic Lateral Plate Mesoderm

Bone

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7
Q

Where do the Fascia and Blood Vessels of the upper extremity come from?

A

Somatic Lateral Plate Mesoderm

(They are part of the Connective Tissue)

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8
Q

What is the “Limb Forming Mesoderm” made of?

A

Pariaxial and Somatic Lateral Plate Mesoderm

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9
Q

What stimulates the Surface Ectoderm to become the Apical Ectodermal Ridge?

A

FGF 10

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10
Q

What is the Apical Ectodermal Ridge made of?

A

Surface Ectoderm

The Apical Ectodermal Ridge is just a thickening of the surface ectoderm that was already there in response to FGF 10

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11
Q

What releases FGF 10?

A

The Limb - Forming Mesoderm

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12
Q

What releases FGF 4 and 8?

A

The Apical Ectodermal Ridge

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13
Q

What do FGF 4 and 8 do?

A

Stimulate growth of the Limb-Bud Mesoderm

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14
Q

What “fates” certain regions of the Limb-Forming Mesoderm to become certain bones?

A

Concentration gradients of signaling molecules.

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15
Q

What does the Stylopod give rise to?

A

Humerus and Femur

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16
Q

What does the Zeugopod give rise to?

A

Ulna/Radius

Tibia/Fibula

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17
Q

What does the Autopod give rise to?

A

Carpals/Metacarpals and Digits of the Hand

Tarsals/Metatarsals and Digits of the Foot

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18
Q

When do the Hand and Foot Plates Develop?

A

Week 5?

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19
Q

When do the Digital Rays of the Hand develop?

A

Week 6

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20
Q

When do the Digital Rays of the Feet develop?

A

Week 7

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21
Q

When do the limbs rotate?

A

Week 7

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22
Q

When do the long bones begin to ossify?

A

Week 7

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23
Q

When do we start to separate our digits?

A

Week 8

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24
Q

What pro-apoptotic family is responsible for separating our digits?

If these are down-regulated, what conditions might we see?

A

BMP’s

Webbed fingers or Syndactyly

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25
Q

When do Chondrification Centers appear?

A

Week 5

26
Q

During Week 6, what is the status of the limb skeleton?

A

The entire limb skeleton is cartilage during Week 6.

27
Q

In what region of the embryo is the limb bud forming?

A

The Cervical Region

28
Q

In what region is the leg bud forming?

A

The Lumbosacral Region

29
Q

When do Motor Axons from the spinal cord enter the limb buds?

A

Week 5

30
Q

What gives rise to motor neurons?

A

Neural Tube (Neuroectoderm)

31
Q

When is the Brachial Plexus formed in the embryo?

A

Week 5

When the Motor Neurons enter the Limb Bud

32
Q

How do Sensory Neurons decide where they are going to develop?

A

They follow the Motor Neurons

33
Q

What myelinates the neurons of the peripheral nervous system?

What gives rise to these?

A

Schwann Cells

Neural Crest Cells

34
Q

Does the upper limb rotate Medially or Laterally?

A

Laterally (90°)

35
Q

Does the lower limb rotate medially or laterally

A

Medial (90°)

36
Q

What is the first branch from the Aorta that goes into the limb bud?

What does that structure immediately give rise to?

A

Intersegmental Arteries

Primary Axial Artery

37
Q

What two arteries does the Primary Axial Artery of the Upper Limb become?

A

The Brachial Artery

Common Interosseous Artery

38
Q

What happens to the Common Interosseous Artery and the Brachial Artery to make them form the adult structure?

A

Remodeling

39
Q

What is the common name for Talipes Equinovarus?

A

Club Foot

40
Q

What demographic is more likely to aquire Club Foot?

A

Males (Twice as likely)

41
Q

What causes club foot? (2 causes)

A

Abnormal Limb Rotation

OR

Oligohydramnios

42
Q

What demographic is susceptible to Developmental Hip Dysplasia?

A

More common in Females

43
Q

What is Developmental Hip Dysplasia?

A

Under development of the Acetabulum of the “hip bone”

OR

Generalized joint laxity in the hip

44
Q

What determines the position of the limbs along a cranial / caudal axis?

A

HOX genes

45
Q

What determines the types and the shapes of bones?

A

HOX genes

46
Q

What maintains the dorsal patterning for the upper limb?

A

Wnt7

I WNT a better name for the dorsal patterning signal

47
Q

What maintains the ventral patterning for the upper limb?

A

BMPS

_B_li_mps_ (BMPS) have Vents

48
Q

What determines the Posterior side of the upper limb?

A

The Zone of Polarizing Activity (ZPA)

49
Q

The Zone of Polarizing Activity (ZPA) releases what two signaling molecules?

A

Retinoic Acid

Sonic Hedgehog

50
Q

What can loss of ZPA cause?

A

Lack of Posterior Elements

(Like the little finger and the Ulna B.)

51
Q

What causes Polydactyly?

A

Upregulation of ZPA

52
Q

What might cause you to have pinky fingers on both the anterior and side of the hand?

A

Duplication of ZPA

53
Q

Which are formed first, Posterior Elements or Anterior Elements?

A

Posterior Elements

54
Q

In what week might the error that leads to polydactyly of the hands occur?

A

Week 6

55
Q

In what week might the error that leads to syndactyly occur?

A

Week 8

(when apoptosis occurs)

56
Q

When does primary ossification occur?

A

Week 12

57
Q

When might the error that leads to Club Foot occur?

(Assuming it’s not due to Oligohydramnios)

A

Week 7

58
Q

What disease was caused by Thalidomide?

What weeks were molested by the drug?

A

Meromelia

Weeks 3, 4, and 5

59
Q

What might lead to syndactyly?

A

Downregulation of BMPs

60
Q

What might lead to Ectrodactyly

What is Ectrodactyly?

A

Downregulation of the center of the Apical Ectodermal Ridge

Split Hand / Lobster Claw

61
Q

What is Arthrogryposis?

A

Congenital Joint Contracture