WEEK 12/1 > LIMB DEVELOPMENT Flashcards
Embryo
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
Fetus:
Period: Week 9 until birth (36-40 weeks)
Development: Structural modification, functional development
Potential to function outside the uterus
Estimating Embryo Age
Methods:
Last normal menstrual period
Crown-rump (CR) length measurement
Staging based on comparison with standard embryo series (e.g., Carnegie series)
Trilaminar Embryo
Three Layers: Ectoderm, Mesoderm, Endoderm
Ectoderm
Ectoderm: Epidermis, Neural tube, Neural crest (Central and peripheral nervous system)
Mesoderm
Paraxial, Intermediate, Lateral divisions
Lateral Mesoderm
Dorsal somatopleuric and Ventral splanchnopleuric regions
paraxial mesoderm
Limb skeletal muscle
Somites
Morphological divisions of paraxial mesoderm - trunk development
postcranial segmentation
Bilateral, segmented units involving ectoderm and mesoderm
where do limb bones form from
from cartilage, except the clavicle.
where do cartilage cells arise fro m
lateral somatopleuric mesoderm.
when does ossification start at
8 weeks
what do the bones have
primary and secondary ossification centres
when do all bones fuse. by
early adulthood
where does limb skin develop from
ectoderm (epidermis) and lateral somatopleuric mesoderm (dermis).
Upper limb skin
C4 to T2 segments. Lower limb skin: L2 to L4, L5, and S1 to S3 segments.
upper limb dermatomes
align with lateral border; lower limb dermatomes align with anteromedial border.
where do the muscles develop from
paraxial somitic mesoderm.
where do the myoblasts migrate from
into developing limb
where do connective tissue components form from
from lateral somatopleuric mesoderm.
where do the muscles originate from
myotomes (segmented somitic mesoderm).
what does the epaxial part form
the back
what does the hypaxial part divide into
dorsal and ventral regions.
when do muscles develop
by week 8, with gross movements at around 16 weeks.
where do motor cells derive from
neural tube, sensory fibers from neural crest.
when do motor fibres migrate into limb
around week 4 or 5
what do spinal nerves divide into
dorsal and ventral primary rami
what does the rami form
posterior and anterior divisions of plexuses.
what do the axons do
reorganize and proceed down the limb, corresponding to peripheral nerves.
