Lecture: Butaric - Embryology Flashcards Preview

Anatomy Lower Limb > Lecture: Butaric - Embryology > Flashcards

Flashcards in Lecture: Butaric - Embryology Deck (37):
1

4 weeks you see ...

lower limb bud

2

6-7 weeks you see ...

digital rays and bone precursors

3

8 weeks you see ...

differentiated toes and bone

4

when is the formation of trilaminar disc?

week 3

5

the skin, CNS, and neural crest cells are derived from what?

ectoderm

6

what are muscle, bone and connective tissue derived from?

mesoderm

7

the inner lining of the gut tube is derived from what embryological structure?

endoderm

8

cranial/caudal is the embryo is equivalent to _________ in the adult.

medial/lateral

ex: in embryo, the big toe is cranial. In the adult, the big toe is medial.

9

At what level do the lower limb buds form?

L2-S2

10

Describe the outer and inner layers of the lower limb bud?

Outer ectoderm layer w/ apical ectodermal ridge AER

Inne rcore of mesenchyme

11

what is the role of AER apical ectodermal ridge?

initiates and controls limb growth with HOX genes

12

_______ are responsible for initial division of mesenchymal cells and segmentation (leg vs. thigh elements)

HOX genes

13

Removal or non-maintenance of AER results why?

in arrested development of limb

14

amelia

entire limb missing

15

meromelia

part of limb missing

16

Describe toe formation in week 7 and 8.

Early week 7:
- distal limb bud flattens into foot plate
- 5 digital rays appear

Week 8:
- apoptosis of tissue between rays creates separation of toes

17

cartilage models of future toe bones

condensed mesenchyme

18

failure of toes to separate

syndactyly

19

development of extra digital ray

polydactyly

20

cleft foot or hand, caused by failure of middle digital rays to develop

ectrodactyly

21

what is the early blood supply to the limb buds?

primary axial/axis artery

will mainly disappear and be replaced by external iliac branches

22

when do mesenchymal precursors to cartilage begin?

week 5

23

which parts of the precursor cartilages start to chondrify first?

more cranial elements start to chondrify first (distal phalanges last)

week 6-8

24

when does ossification begin?

week 7-12

the lg. long bones ossify first, but some tarsal don't even start ossifying until post-natal period ***

ossification and fusion of bones continues to adulthood

25

myogenic cells differentiate into ...

myoblasts

myogenic cells from derm-myotomes migrate into lower limb bud and differentiate into myoblasts / aggregate around developing bones / separate into extensor (dorsal) and flexor (ventral) compartments

26

neurogenesis into lower limb begins around...

week 5

27

all lower limb nerves are part of ...

lumbosacral plexus

28

which enters the limb bud first motor and sensory axons?

motor axons FIRST arise from spinal cord and enter into developing muscle masses of limb buds

sensory axons from neural crest cells follow AFTER motor axons

29

schwann cells are derived from...

neural crest cells

supporting schwann cells myelinate axons

30

describe the dermatomes in the embryo compared to an adult

in embryo: follow cranial to caudal pattern

in adult: follow superior-ventral down and up to superior-posterior pattern

31

which limb rotates medially?

lower limb rotates 90 degrees MEDIALLY
upper limb rotates 90 degress LATERALLy

at week 8

32

Adult dermatomes
inguinal ligament
anterior knee (patella)
medial side of foot, great toe
posterior thigh, leg
lateral side of foot

L1
L3,4
L4,5
S1,2
S1

33

great toe medial dermatome

L4-5 ***

34

little toe lateral dermatome

S1

35

describe a clubbed foot

congenital talipes equinovarus

foot is inverted, with sole pointed mediall

tendons (including Achilles' tendon) are shortened

36

critical period for LL development

24-36 days post-fertilization

37

summary of key points

- end week 4 limb bud consists of mesenchyme surrounded by ectoderm
- AER and HOX genes promote limb growth
- week 7 digital rays appear, week 8 digits separate by apoptosis
- bones: from mesenchymal precursors (week 5) follow endochondral ossification (beginning week 7)
- muscles: from myogenic cells, organized as myotomes and by extensor/flexor compartments
- dermatomes: follow myotome organization and relate to medial 90 rotation of lower limb