Upper limb Development Embryo

Question 1

what week does upper limb formation begin

Answer 1

week 4

Question 2

upper limb development is marked by the appearance of what

where does extend from

Answer 2

upper limb bud

ventrolateral trunk

Question 3

where do the upper limb buds derive from

Answer 3

proliferation of mesenchymal cells in the parietal (somatic) layer of lateral plate mesoderm

of the ventrolateral body wall

Question 4

the mesencyhmal core (that forms upper limb buds) is covered by what germ layer

Answer 4

ectoderm

Question 5

true or false

the upper limb begins development 1-2 days before the lower limbs

Answer 5

true

Question 6

the critical perod of development for the upper limb start from what week until what week

Answer 6

begins development in week 4
critical period goes into week 8

Question 7

true or false

the arms end up growing much faster than the lower limbs because they start development first

Answer 7

false. By the end of the critical time period for limb development, the upper and lower limbs are almost synchornized in their devlopmental progress

Question 8

true or false

teratogen exposure during weeks 4-8 is more likely to impact upper limbs and not the lower limbs

Answer 8

true. this is due to the difference in initial development. expsure in the cirtical time period for the limb development may only impact upper limbs

Question 9

true or false

past week 8, a tertatogen could affect both the arms and legs, or just the lower limbs. not as impacted on the arms because of its developmental time period

Answer 9

true. the arm develops during the critical period betwen weeks 4-8, so after week 8 it is more likely to equally affect the arms and legs, or just the legs

Question 10

the upper limb primarly develops from what three specific germ layers

Answer 10

1. dermamyotome of the paraxial mesoderm (somites)
2. parietal (somatic) layer of lateral plate mesoderm
3. ectoderm

Question 11

what part of the upper limb stems from the dermamyotome

Answer 11

migration from hypomere portion> upper limb bud

muscles of the upper limb

Question 12

what part of the upper limb stems from the parietal (somatic) layer of the lateral plate mesoderm

Answer 12

bones and dermis of the upper limb

Question 13

what part of the upper limb stems from the ectoderm

Answer 13

epidermis of the upper limb

Question 14

explain the growing upper limb bud into the humerus, digits, ulna, radius

Answer 14

ectoderm at apical end of upper limb bud thickens> apical ectodermal ridge (AER)> induces mesenchyme to remain undifferentiated > proliferate> upper limb continues to grow> commits to development of specific tissues during week 4-5

Question 15

true or false

cells further from the AER begin to differentiate into cartilage in a proximal to distal direction

Answer 15

true. the cells closer to the trunk begin to differentiate into cartilage and muscle, growing from a proximal to distal direction

Question 16

when does finger formation begin

Answer 16

week 5-6

Question 17

distal portion of limb bud becomes flattened and forms

Answer 17

hand plate

Question 18

mesenchyme in the hand plate condenses and forms

typically how many

Answer 18

distal rays

5

Question 19

what three things contribute to the lengthening of the digits

Answer 19

1. 5 segments of AER (notches between digital rays)
2. cell death of intervening tissue between rays (notches)
3. further deveolopment of cartiliginous digital rays

Question 20

what kind of ossification are the upper limb bones and shoulder girdle formed with

what does this mean

Answer 20

endochondral ossification

cartilage forms first then bone

Question 21

what kind of ossification is the clavicle formed with

Answer 21

intramembranous ossification

Question 22

what week is the first cartilage model of the upper limb bones apparent

Answer 22

week 6

Question 23

what week does endochondral ossification begin

Answer 23

week 8

Question 24

describe how ossification begins

Answer 24

cartiligaginous model is invaded by a blood vessel called nutrient artery> primary ossification center> from the primary ossification center in the diaphysis endochondral ossification gradually progresses toward the end of the cartilaginous model

Question 25

what week are primary ossification centers found in the uppper limb bones

Answer 25

12th week | humerus, radius, & ulna

Question 26

# true or false the diaphysis and epiphyses are both usually not completely ossified at birth

Answer 26

false. the diaphysis is completely ossified (usually) but the epiphyses is still cartilaginous

Question 27

when do secondary ossification centers arise in the epiphyses ? what do they cause to form?

Answer 27

shortly after birth a temporary cartilage plate that remains betweenn diaphyseal and epiphyseal ossification centers (growth plate)

Question 28

what is the significance of the growth plate

Answer 28

growth in the length of bones

Question 29

after birth, where does endochondral ossification proceed

Answer 29

on both sides of the growth plate, but not in the region of the growth plate allows for continued lengthening of the bone

Question 30

# true or false the epiphyseal/growth plate never dissapears as we keep growing

Answer 30

false. late in adolescence, the epiphyseal/growth plates dissapear and the epiphyses unite with the diaphysis of the bone

Question 31

# true or false there are two growth plates on long and short bones

Answer 31

false. there is one on each end of the bone in long bones (2), and only 1 growth plate at one end in short bones

Question 32

muscles of the upper limb develop similarly to the axial muscles of the trunk. Explain how

Answer 32

both arise from the hypomere of the dermamyotome (somites of the paraxial mesoderm) and move ventrally

Question 33

what spinal nerve levels does the upper limb bud arise

Answer 33

adjacent to the C4-T2 | level of the somites

Question 34

what week do the myogenic precursors of the limb start budding

Answer 34

week 5

Question 35

what is the pattern of muscled determined by in the upper limb | which was made from which germ layer

Answer 35

mesenchymal core | parietal somatic layer of lateral plate mesoderm

Question 36

how is the innervation of the upper limb determined | and from what germ layer did it arise

Answer 36

hypomere | somite < paraxial mesoderm

Question 37

what week do the upper limbs rotate ? in which direction? how many degrees?

Answer 37

in week 7 laterally 90 degrees

Question 38

before the upper limbs rotate, how are they growing? | specifically how are the flexor and extensor compartments placed?

Answer 38

the flexor compartments are placed ventrally, extensors are placed dorsally and they elongate in lateral and caudal directions

Question 39

at 5 weeks, the upper limb bud is elongating. At 6 weeks what is happening with the upper limb orientation? how does the orientation of the elbow, thumb, and forearm extensor/flexor compartments change?

Answer 39

the upper limb bends anteriorly so the elbows point laterally and the palms face the trunk. at 7 weeks, the thumb is lateral, the elbow comes to a point dorsally, extensor is posterolateral, flexor is anteromedial

Question 40

# true or false amniotic band syndrome is assocaited with major and minor differences of the upper limb

Answer 40

true

Question 41

# true or false presence of polyhydrmnios is commonly associated with limb differences

Answer 41

false. the presence of oligohydramnios is associated with upper limb differences due to the restricted space and mechanical influence of decrease amniotic fluid

Question 42

describe the differences between amelia, meromelia, and phocomelia presentation and causes

Answer 42

amelia: absence of one or more limbs due to supression of limb bud development during the early part of the 4th week meromelia: partial absence of at least one limb due to the arrest of growth of one or both limbs during the 5th week phocomelia: presence of hands (very short upper limbs with hands) attached to the torso due to failure of the uppper limb bud to elongate (weeks 4-5) | all have to do with limb bud

Question 43

what is cleft hand/split hand and how does it happen

Answer 43

appears as a forked hand thought to be failure of one or more of the digital rays to form (week 6) appear to be sporadic (no apparent cause) | form of ectrodactyly> absent digit

Question 44

what is polydactyly and how does it happen

Answer 44

presence of extra (supernumerary) digits occurs from the formation of additional complete or partial digital rays typically medial or lateral thought to be sporadic/family history also a factor in some cases

Question 45

what is syndactyly and how does it happen | how common is it

Answer 45

webbed or joined fingers lack of cell death within the tissue between the digital rays (week 7-8) most common upper limb difference

Question 46

what are the three forms of syndactyly

Answer 46

simple : only soft tissue complex: bone or cartilage as well as soft tissue complicated: abnormally shaped, extra or missing bones | typically between third and fourth digits, family history apparent

Question 47

what is poland syndrome clinical presentation and cause

Answer 47

absence of at least a portion of the pectoralis major muscle, but additional muscles may also be missing on the affected side nipple and areola are displaced may be accompanied by differences in the development of digits, shortened radius, ribs etc cause is unknown. thought to be a lack of blood supply during week 6 to the affected region