Limb Embryology Flashcards
What genes regulate proximodistal patterning?
Homeobox genes
When does the upper and lower limb bud appear?
Upper = day 24
Lower = 1-2 days later
HOX gene expression results from a combination of the expression of what?
(3 things)
SHH
FGF’s
WNT-7a
What HOX genes are expressed by upper limb?
HOXd 9-13
Limb buds elongate by the proliferation of what?
Mesenchyme
The upper limb buds develop opposite what?
The lower limb buds develop opposite what?
Caudal cervical segments
Lumbar and sacral segments
At the apex of each limb bud the ectoderm thickens to form what?
An apical ectodermal ridge (AER)
What is the apical ectodermal ridge (AER)?
Multilayered epithelial structure
Exerts an inductive influence on the limb mesenchyme
The mesenchyme adjacent to the AER consists of undifferentiated rapidly proliferating cells whereas mesenchymal cells proximal to it differentaite into blood vessels and cartilage bone models
How do hand and foot plates develop?
Distal ends of the limb buds flatten into paddle-like hand plates and flipper like foot plates
By the end of the 6th week, mesenchymal tissue has condensed to form digital rays
During the 7th week digital rays are formed in the foot plates
Apoptosis is responsible for the tissue breakdown in the interdigital regions.
What is this mediated by?
Bone morphogenetic proteins
Cartilaginous precursors of the limb bones develop by chondrification within the mesoderm in what week?
6th week
primary centres of ossification appear in which weeks in response to what?
8-12th week
Response to growth factors
Endochondral ossification occurs for all bones of the limbs except what?
Clavicle
membranous ossification
How do the upper and lower limbs rotate?
Upper limbs rotate 90 degrees laterally so that extensors are on the lateral and posterior surfaces (and the thumb us lateral)
Lower limbs rotate 90 degrees medially so that the extensors are on the anterior surface (and the big toe is medial)
Peripheral nerves grow from the developing limb plexus into the mesenchyme of the limbs during which week?
5th
What is a total absence of limbs called?
Amelia
What is a partial absence of limbs called?
meromelia
What is it called when some long bones are absent?
Phocomelia
What is it called when all bones and parts are present but they are small?
Micromelia
What is the genotype of lobster claw foot?
Autosomal dominant
What is polydactyly?
What causes it?
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 indiced
What is syndactyly?
What are its two types?
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
What is club foot also known by?
Talipes Equinovarus
What does club foot look like?
Sole of foot is turned medially and the foot is inverted
What are the causes of club foot?
Multifactorial (genetic and environmental factors)
?Abnormal positioning or resticted movement of the fetus’s lower limb in the utero
What causes congenital dislocation od the hip in 15% of infants?
Abnormal development of acetabulum
