MSK - Development Of The Limbs Flashcards
What do somites develop into? (3)
Dermatone - skin
Myotome - muscles
Sclerotome - bones
What is a somite?
Organisation of paraxial mesoderm into segments.
Somites are bilaterally paired blocks of paraxial mesoderm that form along the head to tail axis of the developing embryo.
1st appear at day 20 in the occipital region.
31 in total
When do limb buds become visible?
End of fourth week of development.
Where do they become visible?
Ventro-lateral body wall
Which limb bud appears first? Upper or lower limb bud?
Upper limb bud appears first followed by the lower limb bud 1 to 2 days later.
What do the limb buds consist of?
Mescenchymal core covered by layer of cuboidal ectoderm
Where is the anterior and posterior axis in the embryo?
Anterior towards the head
Posterior towards the tail
Remember in the adult
Superior = head
Anterior = Tail
What is the proxio-distal axis?
Base of the limb to tips of the digits
Where does the limb bud come from?
Activation of mesenchyme within lateral mesoderm.
Derived from the somatic later of lateral plate mesoderm
What is the difference between Somatic and Splanchic
Somatic - to do with the body
Splanchic - to do with viscera
What contributions to the limb skeleton?
Lateral plate mesoderm
How does the limb bud elongate?
Proliferation of the mescenchyme core. Lots of tissue created not well differentiated
What is the name of the thickened ectoderm at the apex of the limb bud?
Apical ectodermal ridge (AER)
What is the importance of the apical ectodermal ridge?
Critical for limb bud outgrowth
Orchestrates limb development proximal to distal
Final stage is appearance of paddles
AER then regresses - gradually at first then almost entirely.
What does the apical ectodermal ridge do?
Exert an inductive influence on the adjacent mesenchyme, causing it to remain undifferentiated
As the limb grows, what happens to the cells furthest from the apical ectodermal ridge (AER)?
Proximal mesenchyme begins to differentiate into cartilage and muscle.
Molecular signals from the AER can only communicate to cells that are closest to it so the furthest part differentiates.
What would happen in the absence of the apical ectodermal ridge (AER)?
The limb bud would differentiate