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Flashcards in Limb development Deck (29):
1

Which process forms the mesoderm?

Gastrulation

2

Describe how mesoderm is formed during gastrulation

Invading epiblast cells travel through the primitive streak to form the mesoderm

3

What happens as a result of gastrulation?

Formation of the 3 definitive germ layers

4

Name the 3 germ layers

Ectoderm
Mesoderm
Endoderm

5

What happens to the mesoderm when it is formed?

Undergoes further changes to form paraxial, intermediate and lateral plate mesoderm

6

What does the paraxial mesoderm give rise to?

Somites

7

Which part of the mesoderm is important for limb development?

Lateral plate mesoderm

8

Describe the first signs of limbs

Small outpocketings from the body

9

When do the first signs of the limbs appear?

During week 5

10

What do the limb buds contain?

Mesenchyme

11

Where is the mesenchyme in the limb buds made?

From lateral plate mesoderm

12

What can be found at the distal area of the limb bud?

Thickened area called the apical ectodermal ridge (AER)

13

Why is the apical ectodermal ridge important?

Keeps cells at the distal region in a state of proliferation and undifferentiated

14

What happens to cells proximal to the AER as the limb grows?

Able to differentiate

15

What controls the spatial patterning of the limb?

Hox genes

16

What does the limb mesenchyme produce?

All the connective tissues of the limb including tendons, ligaments, fascia, cartilage and bone

17

How are the skeletal elements laid down?

As cartilage in a proximal to distal sequence

18

How is the hand/foot plate formed?

Paddle shaped feature

19

What begins to form from the hand/foot plate?

Digital rays

20

How are fingers and toes formed?

Programmed cell death of tissue between each digital ray

21

What happens after the fingers and toes are formed?

All of the cartilages undergo endochondral ossification to form bone

22

When does ossification of long bones stop?

Adulthood

23

Where do the limb muscles originate?

Somites

24

Describe how limb muscles form

Limb muscle cells delaminate from the somite and migrate into the limb bud

Once in the limb, muscle cells congregate close to the skeletal elements

Muscle cells organise themselves into ventral and dorsal muscle masses which undergo further cleavage to form the individual muscles of the limb

25

Which nerves migrate into the limb to innervate muscles

Ventral primary rami of spinal nerves

26

What is phocomelia?

Where parts of the limb are absent

27

What is syndactyly?

Where there is fusion of the digits

28

What causes phocomelia?

lack of cell proliferation

29

What causes syndactyly?

lack of cell death