Flashcards in Lecture: Butaric - Embryology Deck (37):
4 weeks you see ...
lower limb bud
6-7 weeks you see ...
digital rays and bone precursors
8 weeks you see ...
differentiated toes and bone
when is the formation of trilaminar disc?
the skin, CNS, and neural crest cells are derived from what?
what are muscle, bone and connective tissue derived from?
the inner lining of the gut tube is derived from what embryological structure?
cranial/caudal is the embryo is equivalent to _________ in the adult.
ex: in embryo, the big toe is cranial. In the adult, the big toe is medial.
At what level do the lower limb buds form?
Describe the outer and inner layers of the lower limb bud?
Outer ectoderm layer w/ apical ectodermal ridge AER
Inne rcore of mesenchyme
what is the role of AER apical ectodermal ridge?
initiates and controls limb growth with HOX genes
_______ are responsible for initial division of mesenchymal cells and segmentation (leg vs. thigh elements)
Removal or non-maintenance of AER results why?
in arrested development of limb
entire limb missing
part of limb missing
Describe toe formation in week 7 and 8.
Early week 7:
- distal limb bud flattens into foot plate
- 5 digital rays appear
- apoptosis of tissue between rays creates separation of toes
cartilage models of future toe bones
failure of toes to separate
development of extra digital ray
cleft foot or hand, caused by failure of middle digital rays to develop
what is the early blood supply to the limb buds?
primary axial/axis artery
will mainly disappear and be replaced by external iliac branches
when do mesenchymal precursors to cartilage begin?
which parts of the precursor cartilages start to chondrify first?
more cranial elements start to chondrify first (distal phalanges last)
when does ossification begin?
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
myogenic cells differentiate into ...
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
neurogenesis into lower limb begins around...
all lower limb nerves are part of ...
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
schwann cells are derived from...
neural crest cells
supporting schwann cells myelinate axons
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
which limb rotates medially?
lower limb rotates 90 degrees MEDIALLY
upper limb rotates 90 degress LATERALLy
at week 8
anterior knee (patella)
medial side of foot, great toe
posterior thigh, leg
lateral side of foot
great toe medial dermatome
little toe lateral dermatome
describe a clubbed foot
congenital talipes equinovarus
foot is inverted, with sole pointed mediall
tendons (including Achilles' tendon) are shortened
critical period for LL development
24-36 days post-fertilization