Embryology Flashcards
How does limb development begin in utero
Begins near end of 4th week.
ACtivation of mesenchymal cells in the somatic layer of the mesoderm
Homeobox genes regulate patterning
When do the limb buds appear?
Day 24 upper limb bud
1-2 days later lower limb bud appears
What are HOX genes
genes that determine which skeletal elements are formed
Hox9-13 genes reposnible for forming upper limg. Remove Hoxa 11 and Hoxd 11 and the radius and ulna do not form
How do the limb buds develop?
Limb buds elongate by the proliferation of the mesenchyme
Upper limb buds develop opposite the caudal cervical segments
Lower limb buds form opposite the lumbar and sacral segments
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 of the limb mesenchyme
How does the AER influence the structures around
Mesenchyme adjacent to the AER consists of undifferntiated rapidly proliferating cells.
Mesenchymal cells proximal to it differentiate into blood vessels and cartilage bone models
Describe the process of limb development
What causes the breakdown of the tissue to form digit development
Limb buds Paddle shaped plates Digital rays Notches between rays Webbed fingers and toes Seperate digits of the fingers and toes
occurs between the 4th and 8th weeks
Programmed cell death occurs to break down tissues that arent needed. Mediated by bone morphogenetic proteins
What are the final stages of limb development
Cartilaginous precursors of the limb bones develop by chondirfication within the mesoderm
Primary centres of ossification appear in weeks 8-12 in response to growth factors
Endochondrial ossification for all limb bones except the clavicle
How do the limbs originally develop
Upper limbs rotate 90 degrees laterally so that extensors are in lateral positions
Lower limbs rotate 90 degrees medially so that the extensors are on the anterior surface
What is:
Amelia meromelia phocomelia misromelia polydactly
Amelia- total absence meromelia- Partial absence phocomelia- absence of long bones micromelia- all parts present but small prescence of more than 5 digits on the nads or feet
Why does lobster claw foot
Autosomal dominant trait, critical period of limb development 24-36 after fertilization
What is syndactyly
Common birth defect of hand or foot. Can cause simple webbing or range to fusion of the digital bones.
more common in the foot
Explain congenital clubfoot
Sole of foot is tuned medially and foot is inverted.
Can be cuased by many factor e.g. genetics and environemnt
Abnormal positioning or restricted movement of the fetus’ lower limb in utero
Explain developmental dysplasia of the hip
Abnormal development of the acetabulum
15% of infants with congenital dislocation of the hip
Common after breech deliveries.
