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Musculoskeletal System > Limb Development > Flashcards

Limb Development Flashcards

1
Q

When do upper and lower limb appear compared to each other?

A
  • Paired upper and lower limb buds appear as small elevation of ventrolateral body wall by the 4th week of development.
  • Upper limb buds are visible by day 26 or 27, whereas lower limb buds appear 1 or 2 days later
  • Upper limb buds develop opposite the caudal cervical segment, whereas the lower limb bud develop opposite the lumbar and upper sacral segment
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2
Q

What does a limb bud consist of?

A
  • A mesenchymal core:
    • derived from somatic layer of lateral plate mesoderm

-covered by ectoderm

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3
Q

How does limb development initiate?

A

Activation of mesenchymal cells in the lateral mesoderm starts off the process of limb development (elongation)

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4
Q

Contrast the divisions of mesoderm and what they develop into

A

Paraxial mesoderm- divides into 42-44 pairs of somites

Intermediate mesoderm- urogenital system

Lateral plate mesoderm:
- subdivision of the intraembryonic (secondary) mesoderm

  • forms the connective tissue of the limbs
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5
Q

Somites give rise to:

A

Somites gives rise to:
-sclerotome= vertebrae & ribs

  • myotome= muscle
  • dermatome= connective tissue-dermis
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6
Q

What initiates the development of the limb?

A

The homeobox (HOX) gene initiates the process

  • Activation of mesenchyme induces formation of an Apical ectidermal ridge (AER)
  • Mesenchyme condenses and gives rise to the skeleton & connective tissue
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7
Q

What is the function of the Apical ectodermal ridge(AER)?

A

Apical ectodermal ridge(AER)

  • Ectodermal thinking at the apex of each limb bud
  • Inductive influence on limb mesenchyme
    • Stimulate proliferation of mesenchyme
      • Progress zone
  • Growth and development of the limbs
    • Proximaldistal axis

Interaction between the AER and mesenchyme is essential for limb development

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8
Q

What is the signal center and molecular signal for the proximodistal axis?

A

Signaling center: apical ectodermal ridge(AER)

Molecular signal: fibroblast growth factors (FGF-2, -4,-8)

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9
Q

What are the signaling center and molecular signals of the anteroposterior axis?

A

Signaling center: zone of polarizing activity(ZPA)

Molecular signal: sonic hedgehog (shh)

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10
Q

What are the signaling centers and molecular signal of the dorsi ventral axis?

A

Signaling center- dorsal ectoderm

Molecular signal- Wnt-7a(dorsal)

Signaling center- Ventral ectoderm

Molecular signal- En- 1 (ventral)

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11
Q

Summarize week 4 of limb development

A

28 days

-Limb buds appear as small elevations of the ventrolateral body wall

  • Upper limb buds appear by 26th-27th day
    • Opposite C5-T1 spinal segments

Lower limb buds appear about 2 days later
-opposite L4-S3 spinal segments

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12
Q

Summarize week 5 of limb development

A

32 days of hand and foot plates

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13
Q

What occurs during week 6 and week 7 of limb development?

A

42 days
Week 6
-Mesenchymal tissue in the hand plates condense to form digital ray(finger buds), outlines the pattern of the digits

Week 7
-Mesenchymal tissue in the foot plates condense to form digital ray( toe buds), outlines the pattern of the digits

  • Tissue between digital rays undergoes apoptosis (programmed cell death)
    • Forming notches between the digit rays
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14
Q

What are the events occurring in the 5 the week of limb development?

A

56 days

-fingers and toes are distinct and separated

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15
Q

Summarize limb development, week by week

A

Week 4
-limb buds appear

Week 5
-hand & foot plates formed

Week 6

  • digital rays appear
  • tissue between digital rays undergoes apoptosis
    • form notches

Week 7

  • Upper limbs bend at elbow
  • Fingers are short and webbed

Week 8
-Digits are distinct and separated

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16
Q

What are the positional changes of developing limbs?

A

A. 48 days

  • limbs extend ventrally
  • Hand plates & foot plates face each other

B. 51 days

  • Upper limbs bent at elbows
  • Hands curved over the thorax

C. 54 Days
-Soles of feet medially

D. 56 days

  • Elbows point caudally
  • knees point cranially
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17
Q

How are limbs rotated?

A

Upper limb rotates 90 degrees laterally

  • flexors-anteriorly
  • extensors-posterior

Lower limb rotates 90 degrees medially

  • extensors anterior
  • flexors- posterior
18
Q

Summarize development of cartilaginous bones

A
  • chondrofication centers form during 5th week
  • By 6th week, the entire limb skeleton is cartilaginous
  • Osteogenesis of the long bones begins in the 7th week
    • Primary ossification centers

-Ossification of the carpal and tarsal bones begins in the first year after birth

19
Q

How are bones and limb girdles formed?

A

Bones of the limbs & limb girdles are formed by endochondrial ossification (except for the clavicle)
-mesenchymal cells give rise to a cartilaginous model which subsequently ossifies

20
Q

Summarize ossification of the appendicular skeleton

A
  1. Diaphysis
    • Formed by primary center of ossification
      • Appear by 7th - 8th week
  2. Epiphysis
    • Formed by secondary centers of ossification
      • Appear during first 4 years
  3. Epiphyseal plate
    • Growth plate between diaphysis and epiphysis
    • Adds length to the bone
    • Persist until growth period is over
21
Q

Where are the primary centers for ossification?

A

Primary centers of ossification present in most long bones of appendicular skeleton

Some areas remain cartilaginous
-epiphyses of long bones

-carpus and tarsus

22
Q

What are myotomes?

A
  • Musculature of limbs develops from hypaxial divisions of myotomes
  • Myogenic precursor cells migrate into the limb bud and differentiate into myoblasts
  • As long bones form, myoblasts aggregate and form a muscle mass I; each limb bud
  • This muscle mass separate into flexor and extensor compartments
23
Q

When are dermatomes formed ?

A

Motor axons arise from the spinal cord and enter limb bud during the 5th week

Sensory axons enter limb buds after the motor axons
-use them for guidance

24
Q

Neural crest cells are…

A
  • Precursors of Schwann cells
  • Surround motor and sensory nerve fibers in the limbs
  • Form the neurolemma and myelin sheaths
25
Q

What is a dermatome?

A

An area of skin supplied by a single spinal nerve and its spinal ganglion

Spinal nerves are distributed in the segmental bands & their orderly sequence of distribution can be recognized even after growth of the limbs

26
Q

How are limb arteries developed?

A

Limb buds supplied by branches of the intersegmental arteries

  • Arise from dorsal aorta
  • Form fine capillary network throughout mesenchyme

Primordial vascular pattern
-Primary axial artery & it’s branches

27
Q

What is the frequency of syndactyly?

A

1:2200 births

28
Q

What are the types of syndactyly?

A 
Cutaneous syndactyly(most common limb defect)
  -webbing of the digits-failure of webs to degenerate between 2 or more digits

Osseous syndactyly
-fusion of the bones- failure of development of notches between the digital rays

29
Q

What is polydactyly?

A

Supernumerary digits

  • disruption of anterior posterior pattern
  • inherited as a dominant trait
30
Q

What is club foot(congenital talipes)?

A
  • Talipes equinovarus (is the most common type)
  • Twice more frequently in males as in females
  • Sole of foot is turned medially and foot is inverted
  • Multifactorial pattern of inheritance
31
Q

What is Amelia?

A
  • Complete absence of limbs

- Suppression of limb bud development in the 4th week

32
Q

What is meromelia?

A

Partial absence of limbs

-disturbance of limb development during 5th week

33
Q

What are amelia and meromelia defects caused by?

A
  • genetic factors
  • mutant genes
  • environmental factors
  • vascular disruption and ischemia
34
Q

What are cleft hand and cleft foot (ectrodactyly)?

A
  • absence of one or more central digits
    • Failure of development of one or more digital rays

-Remaining digits are partially or completely fused

  • Rare anomaly
    • Lobster claw deformities
35
Q

What is amniotic band syndrome?

A

Tears in the amnion result in amniotic bands

  • May encircle fetal limbs & digits
    • Ring constrictions
    • Amputations
36
Q

What is the cause of amniotic band syndrome?

A

Cause unknown

-May be due to infection

37
Q

What is the frequency of amniotic band syndrome?

A

About 1:1200 live births

38
Q

What is the frequency of vecterl syndrome?

A

Occurs in 1 in 10,000 to 40,000 births.

39
Q

What is the cause of vecterl syndrome?

A

Caused by the interaction of multiple genetic and environmental factors

40
Q

What are the characteristics of vecterl syndrome?

A
  • vertebral defects
  • anal atresia
  • cardiac defects
  • Tracheo-oesophageal fistulga
  • Renal anomalies
  • Limb anomalies

People diagnosed with VECTERL association typically have at least three of these characteristics

Musculoskeletal System (41 decks)

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