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Human Development (BSC5314) > Limb Development > Flashcards

Limb Development Flashcards

0
Q

What limb buds are seen first, upper limb or lower limb?

A

upper

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1
Q

Where do limb buds first appear?

A

as elevations on ventrolateral body wall

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2
Q

Where do upper limb buds develop from?

A

opposite the caudal cervical somites (C5-T1)

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3
Q

Where do lower limb buds develop?

A

opposite the lumbar and upper sacral somites (L1-S3)

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4
Q

What do limb buds consist of?

A

mesenchyme covered by ectoderm

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5
Q

What are Apical Ectodermal Ridges (AER)?

A
  • thick band of ectoderm that induces limb development

- control patterning of limb in proximodistal axis

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6
Q

Secretions produced in what induce the formation of the zone of polarizing activity (ZPA)?

A

AER

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7
Q

What is the zone of polarizing activity?

A
  • group of mesenchyme cells in posterior margin of limb bud

- control patterning of limb in the ant-post axis

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8
Q

Adjacent to AER what is mesenchyme doing?

A

rapid proliferating

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9
Q

In week 6 digital rays form in mesenchyme of what?

A

handplate

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10
Q

What happens to the intervals between digits which are filled with loose mesenchyme in week 7?

A

apoptosis

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11
Q

What happens in week 8?

A
  • 1* ossification centers in diaphyses

- separate fingers and toes visible

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12
Q

When do most 2* ossification centers appear?

A

postnatally

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13
Q

When do carpels and tarsals ossify?

A

1st yr after birth

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14
Q

Where doe synovial joints form?

A

in interzonal mesenchyme between developing bones

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15
Q

What does peripheral mesenchyme form in synovial joints?

A

joint capsule, synovial membrane, other ligaments

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16
Q

What do central mesenchyme in synovial joints do?

A

disappears to become joint cavity

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17
Q

What happens with restricted fetal movement?

A

abnormal limb development

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18
Q

What are the most critical days for limb development?

A

day 24-36

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19
Q

What is worse, early exposure or late exposure to teratogens?

A

early

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20
Q

What is thalidomide?

A
  • sedative and antinauseant given to pregnant women
  • assoc. with many severe limb defects
  • nowadays treatment for leprosy etc
21
Q

What are some other causes for limb anomalies?

A

genetics
environmental factors (drugs)
ischemia
low amniotic fluid (oligohydramnios)

22
Q

What is amelia?

A

absence of limbs

23
Q

What is meromelia?

A

absence of part of a limb

24
Q

What is cleft hand or foot?

A

absence of one or more central digits

- failures of digital rays to form

25
Q

What is syndactyly?

A
  • cutaneous syndactyly
    • webbing of skin between digits due to failure to degeneration of webs
  • osseous syndactyly = fusion of phalanges (3-4th digits/2-3 toes)
    • notches fail to form between developing digital rays
26
Q

What is brachydactyly?

A

shortness of the digits

- due to reduction in length of phalanges
- assoc. with short stature
27
Q

What is polydactyly?

A

more than the usual # of digits

- extra fingers usually medial or lateral 
- extra toes usually lateral
28
Q

What is congenital clubfoot?

A
  • deformity involving the talus
  • sole of foot faces medially and foot inverted
  • restricted mvmt in utero
29
Q

What is achondroplasia?

A
  • common cause of dwarfism
  • disrupted endochondral ossification of long bones
    • limbs short and bowed, forehead bulges
30
Q

How do appendicular mm form?

A

myogenic cells migrate from myotomes of somites and differentiate in limbs into myoblasts => single large mm mass in each limb

31
Q

Muscle mass separates into 2 components, what are they?

A

upper limb
- dorsal component => extensors and supinator
- ventral component => flexors and pronator
lower limb
- dorsal component => extensors and abductors
- ventral component => flexors and adductors

32
Q

Where do ligaments and blood vessels in appendicular mms derive from?

A

limb mesenchyme

33
Q

How do upper limbs rotate?

A

laterally on longitudinal axis more than 90 degrees

34
Q

What are the before and after rotation of upper limb?

A

Before => After

  • Elbows: laterally => dorsally
  • Thumbs: anteriorly => lateral
  • Extensors: dorsal => lateral and posterior aspect
35
Q

How do lower limbs rotate?

A

medially on longitudinal axis less than 90 degrees

36
Q

What are the before and after of rotation on lower limbs?

A

Before => After

  • Knees: lateral => ventrally
  • Big toe: anteriorly => medially
  • Extensors: dorsally => anterior aspect
37
Q

What is the motor innervation of limbs?

A
  • ventral motor axons from spinal cord => dorsal/ventral mm masses
  • result in formation of brachial and lumbosacral plexuses
38
Q

What is the sensory innervation of limbs?

A

-sensory peripheral processes enter limb after motor axons and follow their paths

39
Q

What surrounds both motor and sensory processes? what does it form?

A

neural crest cells - differentiate as Schwann cells

40
Q

What is a dermatome of a limb?

A

segmental area of skin supplied by a single spinal n. and its ganglion
- both dorsal and ventral ramus

41
Q

Where do upper limb dermatomes progress?

A
  • down lateral aspect (C5-7 supply preaxial border)

- back up medial aspect (C8-T2 supply postaxial border)

42
Q

Where do lower limb dermatome progress?

A
  • down anterior aspect (L2-L4 supply preaxial border)

- back up posterior aspect (L5-S3 supply postaxial border)

43
Q

Where is there minimal overlap in dermatomes?

A

ventral axial line

- ant on upper limb and posterior on lower limb

44
Q

What is the cutaneous n. area of limbs?

A
  • skin supplied by a peripheral n.

- usually innervated by terminal br. of more than one spinal n.

45
Q

What kind of sensory loss occurs with a dorsal root injury?

A

parietal sensory loss

46
Q

Where does the primary axial artery form?

A
  • forming as limb bud grows
    • br from intersegmental a.
  • initially grows adjacent to condensed mesenchyme forming the limb bones
47
Q

What does the primary axial artery in upper extremity become?

A
  • brachial a in arm
    • radial and ulnar aa.
  • common interosseous a in forearm
48
Q

What does the primary axial a in lower limbs become?

A
  • deep femoral a.
    • femoral a.
  • ant and post tibial aa.
49
Q

What does the peripheral venous sinus become?

A
  • cephalic and basilic veins in upper extremity

- greater and lesser saphenous vv. in lower extremity

Human Development (BSC5314) (34 decks)

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