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MSK1 > Development of Limbs > Flashcards

Development of Limbs Flashcards

1
Q

Describe what is created from the lateral plate mesoderm

A

Splanchic = circulatory system
Somatic = body cavity, pelvis, limb bones and tendons
Extraembryonic

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2
Q

Describe what is created from the intermediate mesoderm

A

Kidney and gonads

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3
Q

Describe what is created from the paraxial mesoderm

A

Head and somites

Somites = sclerotome, myotome, dermatome

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4
Q

When do upper limb buds form?

A

Day 24

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5
Q

When do lower limb buds form?

A

Day 25-26

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6
Q

What do limb buds form deep to?

A

The apical ectodermal ridge (AER) which is a thick band of ectoderm that the limb buds form deep to

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7
Q

What grows out from that AER?

A

Proliferation of mesenchyme from the lateral plate mesoderm

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8
Q

What is the stylopod region?

A

Humerus or femur

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9
Q

What is the zeugopod region?

A

Radius/ulna or tibia/fibula

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10
Q

What is the autopod region?

A

Carpals, metacarpals, phalanges or tarsals, metatarsals, phalanges

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11
Q

What are the axes of the limb bud?

A

Proximal - Dorsal
Cranial - Caudal
Dorsal - Ventral

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12
Q

Describe the initiation of limb bud growth

A

FGF10 induces the formation of AER and AER secretes FGF8 which positively regulates FGF10 to stimulate more AER

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13
Q

What is the importance of FGF signaling?

A

It is essential for the INITIATION of limb bud development and for the proximal - distal axis to form

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14
Q

What happens if AER is completely removed?

A

NO limb formation

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15
Q

What happens if AER is removed later in development?

A

Loss of distal elements

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16
Q

Meromelia

A

Absence of part of a limb caused by intermediate or late loss of FGF signaling

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17
Q

Amelia

A

Absence of an entire limb caused by early loss of FGF signaling

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18
Q

Phocomelia

A

Loss of long bones with hands/feet attached proximally

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19
Q

What can cause phocomelia?

A

Partial loss of FGF signaling or HOX disruption due to thalomide

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20
Q

Adactyly

A

Absence of digits caused by late loss of FGF signaling

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21
Q

Ectrodactyly

A

Split hand/foot - “lobster claw”

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22
Q

What causes ectrodactyly

A

Partial absence of FGF8 from AER or EEC syndrome

23
Q

What creates the cranial - caudal axis?

A

Zone of polarizing activity (ZPA)

24
Q

What supports ZPA function?

A

SHH!

25
Q

What happens when there is an overexpression of SHH?

A

A second ZPA is created and duplicated digits emerge

26
Q

Polydactyly

A

Dominant trait; presence of supernumary digits where extra digits lack normal growth and musculature

27
Q

What do HOX genes regulate?

A

Cranial - caudal and proximal - distal axes

28
Q

What is a paralog?

A

Genes related due to descent from a common ancestral DNA sequence

29
Q

What hox gene specifies stylopod?

A

HOX9/10

30
Q

What hox gene specifies zeugopod?

A

HOX11

31
Q

What hox gene specifies autopod?

A

HOX12/13

32
Q

Brachydactyly

A

Shortened finger/toe bones due to genetic changes in HOX13 or PTHLH

33
Q

What creates the dorsal surface?

A

Wnt7a

34
Q

What creates the ventral surface?

A

EN1 (engrailed)

35
Q

What gives negative feedback to the Wnt7a?

A

EN1

36
Q

How are individual digits formed?

A

Interdigital mesenchyme apoptosis

37
Q

What stimulates interdigital mesenchyme apoptosis?

A

Increased BMP = Increased cell death

38
Q

When do separate digits fully form?

A

8th week

39
Q

What is syndactyly?

A

Fusion of digits due to no digital rays

40
Q

What are the 2 types of syndactyly?

A

Cutaneous and osseous

41
Q

Cutaneous syndactyly

A

Webbing between digits fails to degenerate; BMP signaling disruption that causes no apoptosis

42
Q

Osseous syndactyly

A

Fusion of bones; HOXD13 mutation

43
Q

Describe how limbs get their muscle mass

A

Dermamyotome from the paraxial mesoderm migrates to the limb bud and differentiates into myoblasts to form the ventral and dorsal muscle masses

44
Q

What does the dorsal muscle mass become?

A

Extensors, ABductors and supinators

45
Q

What does the ventral muscle mass become?

A

Flexors, ADDuctors and pronators

46
Q

What innervates the dorsal muscle mass?

A

Dorsal branches of VENTRAL rami

47
Q

What innervates the ventral muscle mass?

A

Ventral branches of ventral rami

48
Q

List the pathway for arterial supply to the upper limb

A

Dorsal intersegmental A.
Primary axial A.
Brachial A. and common interosseous A.
Ulnar A. and Radial A.

49
Q

List the pathway for arterial supply to the lower limb

A

Dorsal intersegmental A.
Primary axial A.
Deep A. of the thigh, Anterior tibial A., Posterior tibial A.

50
Q

Describe the venous supply

A

Primary axial A, marginal sinus, peripheral vein

51
Q

Which way does the upper extremity rotate?

A

Laterally

52
Q

Which way does the lower extremity rotate?

A

Medially

53
Q

Amniotic bands

A

Adhesions between amnion and fetal structures; prevents growth or pinches off structure

54
Q

Bilateral talipes equinovarus

A

Club foot; caused by oligohydramnios - low amniotic fluid volume reduces fetal movements

MSK1 (29 decks)

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