Development of the Limbs

Question 1

When do digits start forming

Answer 1

8th week

Question 2

When does 1 ossification occur

Answer 2

12th week

Question 3

Cartilage, connective tissue and bone of limbs come from

Answer 3

Somatic mesoderm

Question 4

Development of limbs proceeds in what direction

Answer 4

Proximodistally

Question 5

Stylopod

Answer 5

Humerus and femur

Question 6

Zeugopod

Answer 6

Radius/ulna and tibia/fibula

Question 7

Autopod

Answer 7

Carpels, metacarpals, digits and tarsals, metatarsals

Question 8

Week 5 developments

Answer 8

Hand and foot plates

Chondrification center appears

Question 9

Week 6 developments

Answer 9

Digital ray of hands

Entire limb skeleton is cartilagenous

Question 10

Week 7 developments

Answer 10

Digital rays of feet
Osteogenesis of long bones begins
Rotation of limbs

Question 11

Week 8 developments

Answer 11

Separate digits are formed

Apoptosis

Question 12

When do motor axons from spinal cord enter limbs

Answer 12

5th week

Question 13

How do sensory axons find their way to limbs

Answer 13

They follow motor axons

Question 14

Where do schwann cells come from

Answer 14

Neural crest cells

Question 15

Primary axial artery becomes

Answer 15

Brachial artery in upper limb or deep artery of thigh

Question 16

Talipes Equinovarus

Answer 16

Club foot
Most common musculoskeletal defect
Sole of foot turned medially and inverted
More frequent in males

Question 17

Developmental hip dysplasia

Answer 17

More common in females
Underdevelopment of acetabulum of hip bone
Generalized joint laxity

Question 18

Positioning of limbs is regulated by

Answer 18

Hox genes

Question 19

Scapula, humerus, radius/ulna, carpals, metacarpals positioned by which hox genes

Answer 19

Scapula-9
Humerus-10
Radius/ulna-11
Carpals-12
Metacarpals-13

Question 20

Apical ectodermal ridge proceeds in which way and relies on what signal

Answer 20

Proceeds from proximal to distal and depends on FGF signaling

Question 21

Ventral surface is maintained by what signal and dorsal surface maintained by what signal? What do these signals set up

Answer 21

Dorsal/extensors by Wnt7
Ventral/flexors by BMPS
These signals set up the apical ectodermal ridge AER

Question 22

Anterior posterior patterning is set up by what, and what signal is involved

Answer 22

Zone of polarizing activity on posterior side of limb

Shh signaling from ZPA specifically signals posterior elements

Question 23

Loss of ZPA results in

Answer 23

Loss of posterior elements

Question 24

Upregulation of ZPA results in

Answer 24

Additional posterior elements (polydactyly)

Question 25

Duplication of ZPA results in

Answer 25

Duplication of posterior elements (ex. little fingers on both sides of the thumb)

Question 26

Posterior element formation vs anterior element formation in time

Answer 26

Posterior (little finger/ulna) are formed prior to anterior (radius/thumb)

Question 27

Arthrogryposis

Answer 27

Congenital joint contractures Usually involves more than one joint Thought to be due to neurological defects, muscular abnormalities, joint and contiguous tissue problems, fetal crowding