Embryology Flashcards
What weeks does limb development occur?
week 4 to 8
What is activated at the start of limb development?
mesenchymal cells in the somatic lateral mesoderm
What genes regulate the patterning of limbs?
homeobox
What day does the upper limb and lower limb bud appear?
upper = day 24 lower = 1-2 days later
What HOXa genes are linked to the upper limb?
9-13
How do limb buds elongate?
proliferation of mesenchyme
Where do upper limb buds develop?
opposite caudal cervical segments
Where do lower limb buds develop?
opposite lumbar and sacral segments
What is formed at the end of each bud and how does this happen?
apical ectodermal ridge - AER
ectoderm thickens
Describe the difference between mesenchyme adjacent and proximal to the AER
adjacent = undifferentiated, rapidly proliferating proximal = differentiate into blood vessels and cartilage bone models
In week 6 mesenchyme in hand plates form what?
digital rays
What weeks are digital rays formed in the foot?
7
What mediates apoptosis breakdown of interdigital regions?
bone morphogenetic proteins
What bone does not undergo endochondral ossification? What type of ossification occurs?
clavicle - membranous
Upper limb rotation
90 degrees laterally so extensors are lateral and posterior and thumb is lateral
lower limb rotation
90 degrees medially so extensors medial and anterior and big toe is medial
How is the dermatomal patterns of the limbs achieved?
in week 5 peripheral nerves from the limb plexus grow into mesenchyme of limbs
amelia
total absence
mecromelia
partial absence
phocomelia
some long bones absent
micromelia
all parts present but small
inheritance of lobster claw feet
autosomal dominant
When is the critical limb development period?
days 24-36
polydactyly
presence of more than 5 digits on hands or feet
describe the additional digit(s) in polydactyly
not fully formed and lacks muscular development
cause of polydactyly
inherited or teratogen
Is syndactyly more common in foot or hand?
foot
cutaneous syndactyly
simple webbing
osseous syndactyly
fusion of bones when notches between digital rays fail to develop
action of Thalidomide
disrupts cell adhesion and angiogenesis
some condition Thalidomide is now used to treat
cancer, AIDS, leprosy
What is thalipes equinovarus?
club foot
appearance of foot in club foot q
sole of foot turned medially and foot inverted
cause of club foot
multifactorial
lack of space in womb
Developmental dysplasia of hip
abnormal development of acetablum - breech
generalised joint laxity
