limb development Flashcards Preview

Run through C&M lectures > limb development > Flashcards

Flashcards in limb development Deck (25):
1

when does limb development begin?

mid to late embryonic phase - 4-8 weeks

2

what week are limb buds visible?

end of week 4 - limb buds are visible as outpouchings from the ventrolateral body wall

3

what forms the bones and connective tissue of limbs?

mesenchyme

4

where is the skeletal muscle derived from?

paraxial mesoderm

5

what are somites?

the paraxial mesoderm forms a series of blocks called somites on each side of the neural tube - these differentiate into numerous structures including the muscles of the limbs

6

what does the sclerotome form?

the vertebral column

7

what does the dorsolateral part of the somites form?

the dermomyotome

8

what does the epimere form?

back muscles which are innervated by the dorsal rami of spinal nerves

9

what does the hypomere form?

he muscles of thoracic and abdominal walls and muscles of limbs, they are innervated by the ventral rami of spinal nerves

10

where does the developing upper limb skeletal muscles arise?

the hypomere region adjacent to C5-C8

11

where does the developing lower limb skeletal muscles arise

the hypomere region adjacent to L3-L5

12

how are limb buds innervated?

by branches of the ventral primary rami of spinal nerves

13

when does limb rotation occur?

between 6 and 8 weeks

14

how do the upper limbs rotate?

upper limbs rotate 90 degrees laterally

15

how do the lower limbs rotate?

lower limbs rotate 90 degree medially

16

what is the role of the fibroblastic growth factor?

to induce thickening of the overlying ectoderm along the tip of the limb bud - apical ectodermal ridge

17

what is function of sonic hedgehog?

high conc induce formation of caudal structures - e.g. little finger
low conc induce formation of cranial structures e.g. thumb

18

when does digit formation begin?

week 6 - terminal portion of limb buds flatten to form hand and foot plates

19

how are fingers and toes formed?

by apoptosis

20

what is amelia?

complete absence of a limb

21

what is meromelia?

partial absence of a limb

22

what is phocomelia?

digits develop prematurely - proximal elements of limb absent

23

what is syndactyly?

fused digits
failure of apoptosis

24

what is polydactyly

extra digits - inappropriate SHH expression

25

what is ectrodactyly?

split hand/foot aka lobster claw