Week 19 - Development of the Lower Limb Flashcards
What is organogenesis?
The period encompassing all of the development of organs during the first 8 weeks of embryonic development.
What are morphogens?
Factors that regulate development.
What are teratogens?
Factors that can disrupt developmental processes.
What germ layers and tissues are involved in limb derivation?
Somatic mesoderm from the lateral plate and somites.
When does limb development initiate?
Around the end of week 4.
What are the two types of folding that occur during embryonic development?
- Lateral folding
- Rostro-caudal folding
What is the AER in limb development?
Apical ectodermal ridge that induces limb bud formation.
When is the forelimb initiated during gestation?
Day 26-27.
What are HOX genes responsible for in limb development?
The placement of limb buds.
What is the role of TBX4 and TBX5 in limb development?
- TBX4 induces the hindlimb
- TBX5 induces the forelimb
What do FGF8 and FGF10 do in limb development?
- FGF8 is expressed in the ectoderm and signals to the mesoderm
- FGF10 is expressed in the mesoderm and signals to the AER
What are the three zones of limb segmentation?
- Stylopod
- Zeugopod
- Autopod
What is the ZPA and its function?
Zone of Polarizing Activity that expresses Sonic Hedgehog (SHH) to polarize the limb.
What happens if WNT7a or LMX-1 is lost?
Results in a bi-ventral limb.
What is chondrogenesis?
The process of cartilage formation induced by BMPs.
What occurs at the end of week 6 in limb development?
Separation of digits begins in the hand plate and foot plate.
What is Amelia?
Absence of limb development.
Hemimelia is half absent limb
What is Meromelia?
Partial absence of limb development.
What is Phocomelia?
Absence of the zeugopod.
What is Sirenomelia?
Fusion of limb buds due to failure of mesoderm migration.
What is Polydactyly?
Extra digits resulting from disruption of ZPA induction.
What is Syndactyly?
Failure of digital rays to undergo complete apoptosis.
What is Brachydactyly?
Congenitally shortened digits.
What is Ectrodactyly?
Split hand/foot malformation due to absent central AER rays.
What is the significance of the chick model in developmental biology?
Allowed for surgical alteration and monitoring of limb development.
When do the upper and lower limbs rotate, and in which directions?
- Upper limb rotates dorsally
- Lower limb rotates ventrally
What is the timeline for limb development by the end of week 8?
Limbs have developed externally but require continued differentiation during fetal period.
What is the impact of Thalidomide during pregnancy?
Linked to increased incidence of phocomelia.
What are the effects of limb rotation on muscle positioning?
Flexor and extensor muscles are on opposing sides of the limbs.
Fill in the blank: The limb is derived from both somatic mesoderm from the lateral plate and from the ______.
[somites]
