Embryology Flashcards
When do the limbs start to develop?
what is there activation of?
end of 4th week
- mesenchymal cells in the somatic lateral mesoderm
What appears at day 24
Upper limb bud appear
What genes regulate patterning
Homebox
What genes are expressed in the upper limb
HOXd 9-13
HOX genes determine
which skeletal element formed
If you remove HOXa 11 and HOXd 11 what doesn’t form?
radius and ulna
Limb buds elongate by the proliferation of
Mesenchyme
Upper limb buds develop?
opposite the caudal cervical segments
Lower limb buds form opposite the ?
lumbar and sacral segments
What happens at the apex of each bud
ectoderm thickens to form an apical ectodermal ridge (AER)
Apical Ectodermal Ridge (AER) - features
restricted to end of limb bud
Multilayered epithelial structure
Exerts an inductive influence on the limb mesenchyme
The mesenchyme adjacent to the AER consits of undifferentiated, rapidly proliferating cells
whereas mesenchymal cells proximal to it differentiate into blood vessels and cartilage bone
Development of hand & foot plates
The distal ends of the limb buds flatten into paddle-like hand plates and flipper- like foot plates
By the end of 6th week, mesenchymal tissue in hand plates has condensed to form digital rays
During the 7th week digital rays are formed in the foot plates
Development of hands and feet between the ?
4th and 8th weeks
What is Programmed cell death (apoptosis) is responsible for
tissue breakdown in the
interdigital regions –mediated by bone morphogenetic proteins
Final stages of limb development - how do Cartilaginous precursors of the limb bones develop ?
chondrification within the mesoderm in the 6th week
Primary centres of ossification appear in ?
weeks 8 to 12 in response to growth factors
What ossification takes place for all limb bones except the clavicle
Endochondrial
How do the upper and Lower limbs rotate and what direction/why?
Upper limbs rotate 90 laterally so that extensors are on the lateral and posterior surfaces (and the thumb is lateral)
Lower limbs rotate 90 medially so that the extensors are on the anterior surface (and the big toe is medial)
What happens during the 5th week
peripheral nerves grow from the developing limb plexus
(brachial and lumbosacral) into the mesenchyme of the limbs
Birth Defects of Limbs - total absence vs partial absence
(amelia), partial absence (meromelia)
Some long bone absence
phocomelia
All parts present but small
micromelia)
lobster claw can be inherited as a
autosomal dominant trait
Critical period of limb development: is?
24-36 days after fertilization
What is Polydactyly
Presence of more than 5 digits on the hands or feet
Extra digit is incompletely formed and lacks muscular
development
May be inherited or teratogen induced
What is Syndactyly
Cutaneous vs osseous
Common birth defect of the hand
Cutaneous Syndactyly (simple webbing between the digits) is
- a common limb defect
Osseous Syndactyly (fusion of bones) occurs when notches between the digital rays
fail to develop
Congenital Clubfoot also known as?
TALIPES EQUINOVARUS (Club foot
What is the features of club foot
Sole of the foot is turned medially and the foot is inverted
What causes club foot (2)
Multifactorial (genetic and environmental factors)
2) Abnormal positioning or restricted movement of the
fetus’s lower limb in the utero – Evidence is inconclusive
Developmental Dysplasia of the Hip due to?
Abnormal development of acetabulum
When is dysplasia of the hip common
breech(buttocks) deliveries -? Breech posture during late part of pregnency (abnormal development of acetabulum
2 features of Generalized joint laxity
Multifactorial
Associated with congenital dislocation of hip
