1 - embryology of limbs Flashcards
when does limb development start?
begins near the end of 4th week
how is limb development initiated?
Activation of mesenchymal cells in the somatic lateral mesoderm
what genes regulate patterning during limb development?
homeobox genes
when does upper limb bud appear?
day 24
when does lower limb bud appear?
day 25/26
what HOX genes are expressed in upper limb?
HOXd 9-13
removal of which 2 HOX genes results in radius and ulna not forming?
HOXa and HOXd
how do limb buds elongate?
by the proliferation of the mesenchyme
where do upper limb buds develop?
opposite the lumbar and sacral segments
how is the apical ectodermal ridge (AER) formed?
the ectoderm at the apex of each bud thickens
what is the AER made of?
it is a multilayered epithelial structure
what does the AER influence?
it exerts an inductive influence on the limb mesenchyme
what cells are present in the mesenchyme adjacent to the AER?
undifferentiated, rapidly proliferating cells
what cells are present in the mesenchyme proximal to the AER?
they differentiate into blood vessels and cartilage bone models
what develops into hand and foot plates?
the distal ends of the limb buds
what has occurred by the end of week 6?
mesenchymal tissue in hand plates has condensed to form digital rays
what occurs in week 7?
digital rays are formed in the foot plates
what is mediated by bone morphogenetic proteins?
apoptosis (which accounts for the breakdown in interdigital regions)
when do the Cartilaginous precursors of the limb bones develop by chondrification within the mesoderm?
week 6
what appears in weeks 8-12 in response to growth factors?
1y centres of ossification
what type of ossification is present in all limb bones (except clavicle)?
endochondrial ossification
what type of ossification is present in clavicle?
membranous
how do upper limbs rotate?
90 degrees laterally
how do lower limbs rotate?
90 degrees medially
when do peripheral nerves grow and where do they originate?
week 5 - originate from the developing limb plexus into the mesenchyme of the limbs
term for total absence of limbs at birth?
amelia
term for partial absence of limbs at birth?
meromelia
term for some long bone absence at birth?
phocomelia
term for only small parts absent at birth?
micromelia
how is lobster claw foot inherited?
autosomal dominant
when is the critical period of limb development?
24-36 days after fertilisation
polydactyly?
presence or more than 5 digits on hand/ foot
what 2 mechanisms lead to polydactyly?
inherited or teratogen induced
what is syndactyly?
webbing/fusions of bones
cutaneous syndactyly?
simple webbing between the digits
osseous syndactyly?
fusion of bones
when does osseous syndactyly occur?
when notches between digital rays fail to develop
what does thalidomide cause?
absence/ deformity of long bones - meromelia
side effects of thalidomide?
intestinal atresia, cardiac anomalies
what is congenital clubfoot AKA?
talipes equinovarus
what is congenital clubfoot?
sole of foot is turned medially and the foot is inverted
2 causes of clubfoot?
1 - multifactorial (genetics and environment), 2 - abnormal positioning of foetus’ lower limb in utero
2 causes of developmental dysplasia of the hip?
1 - abnormal development of acetabulum, 2 - generalised joint laxity
does syndactyly occur more in hand/foot?
in feet more often
