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APMLE LEA > Lecture: Butaric - Embryology > Flashcards

Lecture: Butaric - Embryology Flashcards

1
Q

4 weeks you see …

A

lower limb bud

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2
Q

6-7 weeks you see …

A

digital rays and bone precursors

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3
Q

8 weeks you see …

A

differentiated toes and bone

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4
Q

when is the formation of trilaminar disc?

A

week 3

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5
Q

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

A

ectoderm

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6
Q

what are muscle, bone and connective tissue derived from?

A

mesoderm

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7
Q

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

A

endoderm

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8
Q

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

A

medial/lateral

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

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9
Q

At what level do the lower limb buds form?

A

L2-S2

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10
Q

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

A

Outer ectoderm layer w/ apical ectodermal ridge AER

Inne rcore of mesenchyme

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11
Q

what is the role of AER apical ectodermal ridge?

A

initiates and controls limb growth with HOX genes

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12
Q

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

A

HOX genes

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13
Q

Removal or non-maintenance of AER results why?

A

in arrested development of limb

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14
Q

amelia

A

entire limb missing

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15
Q

meromelia

A

part of limb missing

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16
Q

Describe toe formation in week 7 and 8.

A

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
Q

cartilage models of future toe bones

A

condensed mesenchyme

18
Q

failure of toes to separate

A

syndactyly

19
Q

development of extra digital ray

A

polydactyly

20
Q

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

A

ectrodactyly

21
Q

what is the early blood supply to the limb buds?

A

primary axial/axis artery

will mainly disappear and be replaced by external iliac branches

22
Q

when do mesenchymal precursors to cartilage begin?

A

week 5

23
Q

which parts of the precursor cartilages start to chondrify first?

A

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

week 6-8

24
Q

when does ossification begin?

A

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
Q

myogenic cells differentiate into …

A

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
Q

neurogenesis into lower limb begins around…

A

week 5

27
Q

all lower limb nerves are part of …

A

lumbosacral plexus

28
Q

which enters the limb bud first motor and sensory axons?

A

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
Q

schwann cells are derived from…

A

neural crest cells

supporting schwann cells myelinate axons

30
Q

describe the dermatomes in the embryo compared to an adult

A

in embryo: follow cranial to caudal pattern

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

31
Q

which limb rotates medially?

A

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

at week 8

32
Q 
Adult dermatomes
inguinal ligament
anterior knee (patella)
medial side of foot, great toe
posterior thigh, leg
lateral side of foot
A 
L1
L3,4
L4,5
S1,2
S1
33
Q

great toe medial dermatome

A

L4-5 ***

34
Q

little toe lateral dermatome

A

S1

35
Q

describe a clubbed foot

A

congenital talipes equinovarus

foot is inverted, with sole pointed mediall

tendons (including Achilles’ tendon) are shortened

36
Q

critical period for LL development

A

24-36 days post-fertilization

37
Q

summary of key points

A
  • 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

APMLE LEA (23 decks)

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