Limb Development

Question 1

When do the limb buds develop?

Answer 1

Week 4

Question 2

When do the digits form?

Answer 2

Week 8

Question 3

When is the first ossification of bones?

Answer 3

Week 12

Question 4

What it the AER?

Answer 4

The apical ectodermal ridge- this is where the surface ectoderm will bud out and the mesoderm beneath will follow

Question 5

What is released by the AER to stimulate the growth of the mesoderm?

Answer 5

FGF 10

Question 6

What is released by the limb-forming mesoderm to stimulate the growth of the apical ectodermal ridge?

Answer 6

FGF 4 and 8

Question 7

Where does muscle in the limbs come from?

Answer 7

Somatic mesoderm also called the hypomere

Question 8

What tissue does the cartilage from the limbs come from?

Answer 8

The somatic layer of the lateral plate - also called somatic mesoderm

Question 9

What tissue does the connective tissue, like fascia and tendons, come from in the limbs?

Answer 9

The somatic layer of the lateral plate - also called the somatic mesoderm

Question 10

What occurs during the 5th week of limb development?

Answer 10

The distal ends of the limb buds flatten into paddles- and chondrification centers will appear

Question 11

What occurs during the 6th week of limb development?

Answer 11

Mesenchymal tissue in the hand plates will condense to form the digits- the skeleton is cartilaginous at this point

Question 12

What occurs during the 7th week of limb development?

Answer 12

Digital rays of the feet, osteogenesis of the long bones and rotation of the limbs

Question 13

What is occurring during the 8th week of limb development?

Answer 13

There is a separation of digits and apoptosis

Question 14

What is the cell signaling for apoptosis in the digits and when does it take place?

Answer 14

The 8th week and signaled by the BMP

Question 15

What tissue does the muscle of the limbs come from?

Answer 15

They are derived from the dorsolateral cells of the somites( also known as the myotome)

Question 16

What tissue does the motor axon come from and when do they enter the limbs from the spinal cord?

Answer 16

They are derived from the neuroectoderm of the neural tube and they will appear around the 5th week of development

Question 17

What tissue is the sensory axons derived from?

Answer 17

They are derived from the sensory axons- they follow along motor neurons during development

Question 18

How do the upper limbs rotate and what week does this occur?

Answer 18

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

Question 19

Where does the blood supply for the limbs come from?

Answer 19

They derive from intersegmental arteries from the dorsal aorta

Question 20

What is the progression of blood supply development in limb development?

Answer 20

The primary axial artery- then branches into the brachial artery and common interosseous- through angiogenesis the other cells will be developed

Question 21

The position of the limbs along the axis is dictated by what?

Answer 21

The HOX genes control where the limbs develop along the craniocaudal axis

Question 22

How is the proximo-distal growth and patterning dictated in limb development? What is the signaling molecule?

Answer 22

This is dependent on the FGF 4 and 8 from the apical ectodermal ridge and then FGF 10 from the mesoderm

Question 23

What is dorso-ventral patterning?

Answer 23

determining which side is dorsal and which is ventral

Question 24

What is the signaling molecule for dorso-ventral patterning?

Answer 24

The ventral surface is dictated by BMPs and the dorsal surface is dictated by Wnt7

Question 25

What establishes the anterior/posterior patterning of the limbs?

Answer 25

The zone of polarizing activity will dictate the posterior side(5th digit and ulna) of the limb and will release shh and retinoic acid

Question 26

What happens if there is a loss of the zone of polarizing activity?

Answer 26

There will be no posterior elements- missing digits or the ulna

Question 27

What will occur if there is an upregulation of the zone of polarizing activity?

Answer 27

There will be additional posterior elements- will have extra fingers generally on the pinky side

Question 28

What occurs if there is a duplication of the zone of polarizing activity?

Answer 28

There will be a duplication of posterior elements- so you will have extra fingers on either side of the thumb

Question 29

What can occur if there is a disruption of the posterior element formation in limb development?

Answer 29

There can be a loss or disruption of anterior elements, like thumb or radius