Lecture: Butaric - Embryology

Question 1

4 weeks you see …

Answer 1

lower limb bud

Question 2

6-7 weeks you see …

Answer 2

digital rays and bone precursors

Question 3

8 weeks you see …

Answer 3

differentiated toes and bone

Question 4

when is the formation of trilaminar disc?

Answer 4

week 3

Question 5

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

Answer 5

ectoderm

Question 6

what are muscle, bone and connective tissue derived from?

Answer 6

mesoderm

Question 7

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

Answer 7

endoderm

Question 8

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

Answer 8

medial/lateral

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

Question 9

At what level do the lower limb buds form?

Answer 9

L2-S2

Question 10

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

Answer 10

Outer ectoderm layer w/ apical ectodermal ridge AER

Inne rcore of mesenchyme

Question 11

what is the role of AER apical ectodermal ridge?

Answer 11

initiates and controls limb growth with HOX genes

Question 12

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

Answer 12

HOX genes

Question 13

Removal or non-maintenance of AER results why?

Answer 13

in arrested development of limb

Question 14

amelia

Answer 14

entire limb missing

Question 15

meromelia

Answer 15

part of limb missing

Question 16

Describe toe formation in week 7 and 8.

Answer 16

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

Question 17

cartilage models of future toe bones

Answer 17

condensed mesenchyme

Question 18

failure of toes to separate

Answer 18

syndactyly

Question 19

development of extra digital ray

Answer 19

polydactyly

Question 20

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

Answer 20

ectrodactyly

Question 21

what is the early blood supply to the limb buds?

Answer 21

primary axial/axis artery

will mainly disappear and be replaced by external iliac branches

Question 22

when do mesenchymal precursors to cartilage begin?

Answer 22

week 5

Question 23

which parts of the precursor cartilages start to chondrify first?

Answer 23

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

week 6-8

Question 24

when does ossification begin?

Answer 24

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

Question 25

myogenic cells differentiate into ...

Answer 25

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

Question 26

neurogenesis into lower limb begins around...

Answer 26

week 5

Question 27

all lower limb nerves are part of ...

Answer 27

lumbosacral plexus

Question 28

which enters the limb bud first motor and sensory axons?

Answer 28

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

Question 29

schwann cells are derived from...

Answer 29

neural crest cells supporting schwann cells myelinate axons

Question 30

describe the dermatomes in the embryo compared to an adult

Answer 30

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

Question 31

which limb rotates medially?

Answer 31

lower limb rotates 90 degrees MEDIALLY upper limb rotates 90 degress LATERALLy at week 8

Question 32

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

Answer 32

``` L1 L3,4 L4,5 S1,2 S1 ```

Question 33

great toe medial dermatome

Answer 33

L4-5 ***

Question 34

little toe lateral dermatome

Answer 34

S1

Question 35

describe a clubbed foot

Answer 35

congenital talipes equinovarus foot is inverted, with sole pointed mediall tendons (including Achilles' tendon) are shortened

Question 36

critical period for LL development

Answer 36

24-36 days post-fertilization

Question 37

summary of key points

Answer 37

- 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