Embryology - Development of limbs Flashcards
When does limb development begin
~end of week 4
When do the upper and lower limb buds appear
Upper bud appears day 24 lower 1 or 2 days later
What regulates patterning
Homeobox Gene
What causes limb buds to elongate
Proliferation of mesenchyme
where do upper and lower limb buds develop
Upper - Opposite the caudal cervical segments
Lower - Opposite the lumbar and sacral segments
What happens and what is formed at the apex of each bud
The ectoderm thickens forming an Apical Ectodermal Ridge (AER)
What happens to the distal ends of the limb buds and what does this form
They flatten into paddle-like hand and flipper-like foot plates
What is formed by the end of the 6th week
Mesenchymal tissue in the hand plates has condensed enough to form DIGITAL RAYS
What is formed during the 7th week
DIGITAL RAYS are formed in the foot plates
What is responsible for tissue breakdown in the interdigital regions (i.e. what gets rid of webbed fingers)
Programmed cell death/Apoptosis - mediated by Bone Morphogenetic Proteins
(Process absent in Dundee)
What occurs in week 6 (related to joints)
Cartilaginous precursors of limb bones develop by chondrification within the mesoderm
What appear between week 8 to 12 in response to growth factors
Primary centres of ossification
What kind of Ossification occurs in limb bones
Endochondrial ossification
EXCEPT FOR CLAVICLE (membranous)
Describe the rotation of upper and lower limbs
Upper limbs rotate 90 LATERALLY, so that extensors are on LATERAL and POST. surfaces (and the thumb is lateral)
Lower limbs rotate 90 MEDIALLY, so that extensors are on ANTERIOR surface (and the big toe is medial)
When do peripheral nerves grow from the developing limb plexus
During the 5th week
Names for total and partial absence of a limb
Total = Amelia Partial = Meromelia
Some long bone absence
Phocomelia
All parts present but small
Micromelia
Critical period for limb development
24-36 days after fertilisation
What is Polydactyly
Presence of more than 5 digits on hands or feet
Extra digit is incompletely formed and lacks muscular development.
What is Cutaneous and Osseous Syndactyly
Cutaneous - Simple webbing between digits
Osseous - Fusion of bones (occurs when notches between digital rays fail to develop)
Sensitive period for and action of Thalidomide
4-8 weeks
Caused Meromelia if mother ingested it
Disrupting cell adhesion and angiogenesis
Now used in Cancer, Leprosy and AIDS
Describe Congenital Clubfoot
A.K.A. Talipes Equinovarus
Sole of foot is turned medially and foot is inverted
Cause of Talipes Equinovarus/Congenital Clubfoot
Multifactorial (genetic and environmental)
? Abnormal positioning or restricted movement of fetus’ lower limb in utero - evidence is inconclusive.
