Embryology Flashcards
What are the homeobox genes and how do they affect limb development?
- Homeobox (HOX) genes direct the formation of body structures
What HOX genes are expressed in the formation of the upper limb?
- HOXd 9-13
Which layer of the embryo proliferates to allow the limb buds to elongate?
Mesenchyme
Which part of the embryo thickens to form the apical ectodermal ridge?
Ectoderm
What type of cells can be found in the mesenchyme adjacent to the apical ectodermal ridge?
Undifferentiated, rapidly proliferating cells
What cells differentiate into blood vessels and cartilage and bone?
Mesenchymal cells
What is the process responsible for the tissue breakdown in the interdigital regions?
Apoptosis
During which week do the peripheral nerves grow from the developing limb plexus (brachial and lumbosacral)?
5th week
When is the critical period of limb development?
24-36 days after fertilization
What is the total absence of limbs known as?
Amelia
What is the partial absence of limbs known as?
Meromelia
What is the absence of some long bones known as?
Phocomelia
What type of genetic defect is lobster claw foot?
Autosomal dominant
What is the condition called where someone has more than 5 digits on their hands or feet?
Polydactyly
What is the name of the condition when the webbing between the digits fails to dissapear?
Cutaneous syndactyly
During which week of gestation do the limbs begin to appear?
Towards end of 4th week
Upper limb starts to appear around Day 24
Lower limb starts to appear around Day 25-26
Which cells are responsible for the development of the limbs?
Mesenchymal cells
From which germ layer do the limbs form?
Somatic Lateral Mesoderm
Which genes are responsible for limb development?
Homeobox genes
What are the HOX genes made up from?
- SHH
- FGF’s
- WNT-7a
On which part of the limb bud can the apical ectodermal ridge be found?
At the end of the limb bud
Which proteins are responsible for apoptosis?
Bone morphogenetic proteins
During which weeks do the primary centres of ossification appear?
Weeks 8-12
What type of ossification do all of the limb bones (except the clavicle) undergo?
Endochondrial ossification
What type of ossification does the clavicle undergo during embryonic development?
Membraneous ossification
What is the major difference between endochondrial and membranous ossification?
Endochondrial ossification - Cartilage is present
Membranous ossification - No cartilage present
By which process is cartilage formed within the embryo during limb development?
Chondrification
During embryonic development, in which direction do the upper limbs rotate?
Laterally by 90 degrees
The extensor muscles therefore are found on the posterior aspects of the upper limbs
During embryonic development, in which direction do the lower limbs rotate?
90 degrees medially
Extensors are therefore found on the anterior aspect of the lower limb (thigh)
What condition results from maternal ingestion of thalidimide during weeks 4-8 of gestation?
Meromelia
What is this condition known as?
Congenital clubfoot (Talipes Equinovarus)
In what position are the feet of children born with clubfoot?
Sole of foot rotated medially and inverted
How common is clubfoot?
1 in 1,000 newborns
Is syndactyly a common condition?
Yes
Is syndactyly more common in the foot or hand?
Foot
What is osseus syndactyly?
When notches between digital rays fail to develop
