Limb Development Flashcards
When do the limb buds develop?
Week 4
When do the digits form?
Week 8
When is the first ossification of bones?
Week 12
What it the AER?
The apical ectodermal ridge- this is where the surface ectoderm will bud out and the mesoderm beneath will follow
What is released by the AER to stimulate the growth of the mesoderm?
FGF 10
What is released by the limb-forming mesoderm to stimulate the growth of the apical ectodermal ridge?
FGF 4 and 8
Where does muscle in the limbs come from?
Somatic mesoderm also called the hypomere
What tissue does the cartilage from the limbs come from?
The somatic layer of the lateral plate - also called somatic mesoderm
What tissue does the connective tissue, like fascia and tendons, come from in the limbs?
The somatic layer of the lateral plate - also called the somatic mesoderm
What occurs during the 5th week of limb development?
The distal ends of the limb buds flatten into paddles- and chondrification centers will appear
What occurs during the 6th week of limb development?
Mesenchymal tissue in the hand plates will condense to form the digits- the skeleton is cartilaginous at this point
What occurs during the 7th week of limb development?
Digital rays of the feet, osteogenesis of the long bones and rotation of the limbs
What is occurring during the 8th week of limb development?
There is a separation of digits and apoptosis
What is the cell signaling for apoptosis in the digits and when does it take place?
The 8th week and signaled by the BMP
What tissue does the muscle of the limbs come from?
They are derived from the dorsolateral cells of the somites( also known as the myotome)
What tissue does the motor axon come from and when do they enter the limbs from the spinal cord?
They are derived from the neuroectoderm of the neural tube and they will appear around the 5th week of development
What tissue is the sensory axons derived from?
They are derived from the sensory axons- they follow along motor neurons during development
How do the upper limbs rotate and what week does this occur?
The upper limbs will go out proximally then around week 7 they will rotate 90 degrees laterally- The evidence for this is that the thumbs are the lateral side in anatomical position
Where does the blood supply for the limbs come from?
They derive from intersegmental arteries from the dorsal aorta
What is the progression of blood supply development in limb development?
The primary axial artery- then branches into the brachial artery and common interosseous- through angiogenesis the other cells will be developed
The position of the limbs along the axis is dictated by what?
The HOX genes control where the limbs develop along the craniocaudal axis
How is the proximo-distal growth and patterning dictated in limb development? What is the signaling molecule?
This is dependent on the FGF 4 and 8 from the apical ectodermal ridge and then FGF 10 from the mesoderm
What is dorso-ventral patterning?
determining which side is dorsal and which is ventral
What is the signaling molecule for dorso-ventral patterning?
The ventral surface is dictated by BMPs and the dorsal surface is dictated by Wnt7
