Flashcards in Embryology Deck (21):
1
When do the limb buds start to appear?
End of the 4th week
2
What does the remnant of the notochord become?
Nucleus pulposus
3
What structure contains the nucleus pulposus?
Annulus fibrosus
4
What structure is responsible for ensuring elongation of the limb bud?
AER = apical ectodermal ridge
Keeps the cells close to it undifferentiated
5
How many degrees of asymmetry are there in limbs?
3
6
How do the digits develop?
AER regresses so it is only left over what will be the tips of the digits. Therefore the digits continue to grow leaving gaps/thin tissue between. Webbing left behind is then removed by apoptosis.
7
AER marks which boundary?
Dorsal - ventral
8
What does ZPA stand for?
Zone of polarising activity
9
What is the ZPA?
A signalling centre located on the posterior base of the limb bud. It controls patterning and maintains the AER.
10
Limb defects most commonly affect which limb?
Upper limb
11
Define syndactyly
Fusion of digits
12
Define polydactyly
Extra digits
13
Define amelia
Complete absence of a limb
14
Define meromelia
Partial absence of one or more limb structures
15
Which way do the limbs rotate?
Upper limbs = laterally
Lower limbs = medially
16
Define dermatome
A strip of skin supplied by a single spinal nerve
17
Define myotome
A muscle/group of muscles supplied by a single spinal nerve
18
Where do limb buds appear?
Ventro-lateral body wall
19
Where are the sclerotome and dermatomyotome in relation to one another?
Sclerotome = ventral
Dermatomyotome = dorsal
20
Approximately when do the hand and foot plates form?
6 weeks
21