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Anatomy 2 > Limb Development > Flashcards

Limb Development Flashcards

1
Q

Describe the order of limb pattterning

A

Cingulum —> stylopod —> zeugopod —> auto pod

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2
Q

What are some examples of a stylopod

A

Humerus/femur

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3
Q

What are some examples of a zeugopod

A

Ulna + radius

Tibia + fibula

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4
Q

What are some examples of auto pods

A

Wrist + fingers

Ankle + toes

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5
Q

What does the mesenchyme core form and what layers are associated with it?

A

Is undifferentiated tissue

Lateral plate mesoderm and paraxial mesoderm

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6
Q

What does the lateral plate mesoderm form

A

Cartilage, bones, general CT

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7
Q

What does the paraxial mesoderm form

A

Somites, skeletal muscle

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8
Q

What is the ectoderm cover and what are some things it forms?

A

Is the outer germ layer

Out-pocketing of ventral body wall: epidermis of skin, nails, hair

Spinal nerves that will form nervous plexuses

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9
Q

In what fashion do elements of the limb develop

A

Proximal to distal fashion (humerus to distal digits)

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10
Q

What is the product of T-box genes

A

Limb identity (ie pectoral vs thoracic)

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11
Q

What do how genes determine?

A

-where limb buds will form
-what limb will develop at specific location

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12
Q

What does the limb field develop

A

Forms the limb bud

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13
Q

What does the limb bud develop

A

Develops developing limb

MUST START FROM LIMB FIELD

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14
Q

What transcription factors act to induce an epithelium-to-mesenchyme transition that induces the formation of the limb bud?

A

Fibroblast growth factors

T-box transcription factors

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15
Q

Describe the early development stages of the limb bud

A

Originates as ridges in ventrolateral body wall

FOREBUD RIDGE APPEARS FIRST then 1-2 days later, hindbud ridge appears

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16
Q

What 3 axes do the limbs develop along?

A

-proximodistal
-dorsoventral
-craniocaudal

17
Q

How does the proximodistal axes work

A

Fibroblast growth factors acting at the apical ectodermal ridge (AER)

18
Q

How does the dorsoventral axes work

A

Dorsal ectoderm - folding initiated by Wnt7a

19
Q

How does the craniocaudal axes work

A

Sonic hedgehog (Shh) genes acting at the zone of polarizing activity (ZPA)

20
Q

What does the apical ectodermal ridge do

A

-directs pattern formation on proximal-distal axis

Thickened, specialized epithelium located at the dorsoventral border of the tip of the bud

INDUCES PROLIFERATION OF LIMB BUD MESENCHYME

21
Q

What happens once the limb bud acquires its terminal length

A

1) terminal portion of each bud becomes flattened to form hand and footplates
2) 2 constrictions divide the portion of each limb bud
-now have 3 main segments!!!
-stylopod, zeugopod, auto pod

Also, mesenchyme condenses into cartilage models - templates of future long bones

Outer shell —> general shape —> fill in details

22
Q

What directs pattern formation on the dorsal-ventral axis

A

Non-AER ectoderm

Directs dorsal-ventral shape

23
Q

Describe the dorsal-ventral development

A

-precursor muscle cells from ventrolateral myotome of somite migrate to limb bud
-ventral and dorsal muscle groups visible at base of each limb bud
-ventral and dorsal branches of ventral ramus follow growing muscle and provide motor inner action
-muscles are initially segmented but many fuse
-nerve branches from different segments unite into large nerves that serve the dorsal or ventral limb compartments

24
Q

On the cranial-caudal axis, what directs pattern formation

A

Zone of polarizing activity

25
Q

Describe the zone of polarizing activity (ZPA)

A

-area of mesenchyme on caudal border

-gives cranial-caudal identity to differentiating cells

ZPA cells express retinol acid (RA) and Shh

26
Q

What does the Shh gradient induce on the cranial caudal axis

A

Induces nested expression of mesenchymal Hox genes

27
Q

What does ZPA and Shh expression require

A

-input from AER
-input from dorsal ectoderm

28
Q

What is the difference between apoptosis and necrosis

A

Programmed cell death vs traumatic cell death

29
Q

Describe the final limb morphology development

A

-as limb development progresses, the AER breaks up and only covers the emerging digital rays
-interdigital spaces no longer have AER and can now be sculpted by apoptosis

30
Q

What is homology

A

Existence of shared ancestors between a pair of structures, or genes, in different species

31
Q

Describe the horse digit reduction

A

Post patterning changes

-initial limb segments are all laid in cartilage
-digits 1 and 5 are eliminated
-digits 2 and 4 reduction is the result of extensive apoptosis

32
Q

Describe the cattle and swine digit reduction

A

Patterning changes

-digit loss and shift of central axis of foot between digits 3 and 4

33
Q

describe the digit reduction of camels

A

Post-patterning change

Similar to horses

34
Q

What is the order of digit loss?

A

1, 5, 2, 4

35
Q

How do the final position of the limbs form?

A

Forelimb rotates dorsally

Hindlimb rotates ventrally

Anatomy 2 (5 decks)

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