WEEK 12/1 > LIMB DEVELOPMENT

Question 1

Embryo

Answer 1

Period: Fertilization to end of week 8
Development: Cell multiplication, differentiation, organ and limb formation
Organogenesis: Most organs develop from week 4 to week 8

Question 2

Fetus:

Answer 2

Period: Week 9 until birth (36-40 weeks)
Development: Structural modification, functional development
Potential to function outside the uterus

Question 3

Estimating Embryo Age

Answer 3

Methods:

Last normal menstrual period
Crown-rump (CR) length measurement
Staging based on comparison with standard embryo series (e.g., Carnegie series)

Question 4

Trilaminar Embryo

Answer 4

Three Layers: Ectoderm, Mesoderm, Endoderm

Question 5

Ectoderm

Answer 5

Ectoderm: Epidermis, Neural tube, Neural crest (Central and peripheral nervous system)

Question 6

Mesoderm

Answer 6

Paraxial, Intermediate, Lateral divisions

Question 7

Lateral Mesoderm

Answer 7

Dorsal somatopleuric and Ventral splanchnopleuric regions

Question 8

paraxial mesoderm

Answer 8

Limb skeletal muscle

Question 9

Somites

Answer 9

Morphological divisions of paraxial mesoderm - trunk development

Question 10

postcranial segmentation

Answer 10

Bilateral, segmented units involving ectoderm and mesoderm

Question 11

where do limb bones form from

Answer 11

from cartilage, except the clavicle.

Question 12

where do cartilage cells arise fro m

Answer 12

lateral somatopleuric mesoderm.

Question 13

when does ossification start at

Answer 13

8 weeks

Question 14

what do the bones have

Answer 14

primary and secondary ossification centres

Question 15

when do all bones fuse. by

Answer 15

early adulthood

Question 16

where does limb skin develop from

Answer 16

ectoderm (epidermis) and lateral somatopleuric mesoderm (dermis).

Question 17

Upper limb skin

Answer 17

C4 to T2 segments. Lower limb skin: L2 to L4, L5, and S1 to S3 segments.

Question 18

upper limb dermatomes

Answer 18

align with lateral border; lower limb dermatomes align with anteromedial border.

Question 19

where do the muscles develop from

Answer 19

paraxial somitic mesoderm.

Question 20

where do the myoblasts migrate from

Answer 20

into developing limb

Question 21

where do connective tissue components form from

Answer 21

from lateral somatopleuric mesoderm.

Question 22

where do the muscles originate from

Answer 22

myotomes (segmented somitic mesoderm).

Question 23

what does the epaxial part form

Answer 23

the back

Question 24

what does the hypaxial part divide into

Answer 24

dorsal and ventral regions.

Question 25

when do muscles develop

Answer 25

by week 8, with gross movements at around 16 weeks.

Question 26

where do motor cells derive from

Answer 26

neural tube, sensory fibers from neural crest.

Question 27

when do motor fibres migrate into limb

Answer 27

around week 4 or 5

Question 28

what do spinal nerves divide into

Answer 28

dorsal and ventral primary rami

Question 29

what does the rami form

Answer 29

posterior and anterior divisions of plexuses.

Question 30

what do the axons do

Answer 30

reorganize and proceed down the limb, corresponding to peripheral nerves.