Limb development Flashcards
Which process forms the mesoderm?
Gastrulation
Describe how mesoderm is formed during gastrulation
Invading epiblast cells travel through the primitive streak to form the mesoderm
What happens as a result of gastrulation?
Formation of the 3 definitive germ layers
Name the 3 germ layers
Ectoderm
Mesoderm
Endoderm
What happens to the mesoderm when it is formed?
Undergoes further changes to form paraxial, intermediate and lateral plate mesoderm
What does the paraxial mesoderm give rise to?
Somites
Which part of the mesoderm is important for limb development?
Lateral plate mesoderm
Describe the first signs of limbs
Small outpocketings from the body
When do the first signs of the limbs appear?
During week 5
What do the limb buds contain?
Mesenchyme
Where is the mesenchyme in the limb buds made?
From lateral plate mesoderm
What can be found at the distal area of the limb bud?
Thickened area called the apical ectodermal ridge (AER)
Why is the apical ectodermal ridge important?
Keeps cells at the distal region in a state of proliferation and undifferentiated
What happens to cells proximal to the AER as the limb grows?
Able to differentiate
What controls the spatial patterning of the limb?
Hox genes
What does the limb mesenchyme produce?
All the connective tissues of the limb including tendons, ligaments, fascia, cartilage and bone
How are the skeletal elements laid down?
As cartilage in a proximal to distal sequence
How is the hand/foot plate formed?
Paddle shaped feature
What begins to form from the hand/foot plate?
Digital rays
How are fingers and toes formed?
Programmed cell death of tissue between each digital ray
What happens after the fingers and toes are formed?
All of the cartilages undergo endochondral ossification to form bone
When does ossification of long bones stop?
Adulthood
Where do the limb muscles originate?
Somites
Describe how limb muscles form
Limb muscle cells delaminate from the somite and migrate into the limb bud
Once in the limb, muscle cells congregate close to the skeletal elements
Muscle cells organise themselves into ventral and dorsal muscle masses which undergo further cleavage to form the individual muscles of the limb
Which nerves migrate into the limb to innervate muscles
Ventral primary rami of spinal nerves
What is phocomelia?
Where parts of the limb are absent
What is syndactyly?
Where there is fusion of the digits
What causes phocomelia?
lack of cell proliferation
What causes syndactyly?
lack of cell death
