Embryology Flashcards
outline the early stages of limb development…
starts at w4, activation of mesenchymal cells in the somatic lateral plate mesoderm, homeobox genes regulate patterning, at day 24 upper limbs appear, 1-2 days later lower limbs appear
which HOXd genes pattern the upper limb?
HOXd 9-13, remove HOXa 11 and HOXd 11 and the radius and ulna do not form.
limb buds elongate because of the proliferation of the…
Mesenchyme
At the apex of each bud the ectoderm thickens to form an…
apical ectodermal ridge (AER)
what is the AER?
restricted to the end of the 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 models
how does the development of hand and foot plates occur?
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
what does bone morphogenetic proteins mediate?
Programmed cell death (apoptosis) is responsible for the tissue breakdown in the interdigital regions
what are the final stages of limb development?
Cartilaginous precursors of the limb bones develop by chondrification within the mesoderm in the 6th week, Primary centres of ossification appear in weeks 8 to 12 in response to growth factors, Endochondrial ossification for all limb bones except the clavicle (membranous). then the limbs rotate 90 degrees.
dermatome development…
During the 5th week, peripheral nerves grow from the developing limb plexus, (brachial and lumbosacral) into the mesenchyme of the limbs
what is amelia?
total absence of limb
what is meromelia?
partial absense
what is phocomelia?
some long bone
what is micromelia?
all parts present but the limb is small
when Is the period of criticsal limb development?
24-35 days after fertilisation.
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?
Common birth defect of the hand or foot, Cutaneous Syndactyly (simple webbing between the digits) is a common limb defect, More frequent in the foot than in the hand. Osseous Syndactyly (fusion of bones) occurs when notches between the digital rays fail to develop
Thalomide issues?
1957-1962 used as a sleeping tablet and anti-nauseant = partial absence (meromelia) or deformity of long bones (intestinal atresia and cardiac anomalies), Acts by disrupting cell adhesion and angiogenesis, Now used to help cancer, leprosy and AIDS patients
Congenital club foot…
Also known as TALIPES EQUINOVARUS (Club foot), Relatively common birth defect, Sole of the foot is turned medially and the foot is inverted. Cause: 1) 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…
Abnormal development of acetabulum - 15% of infants with congenital dislocation of the hip, Common after breech(buttocks) deliveries -? Breech posture during late part of pregnency (abnormal development of acetabulum and head of femur). Generalized joint laxity, Multifactorial, Associated with congenital dislocation of hip
what mesoderm forms cartilage, bone, deeo fascia and ligaments?
parietal laterl plate mesoderm
what mesoderm forms catilage, bone, deepfascia, ligaments?
Parietal lateral plate mesoderm
Column of mesodermal condensation appears along long axis of bud during
week 5
when does condrification of cartilaginous precursors occur?
week 6
