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Musculoskeletal System > Embryology > Flashcards

Embryology Flashcards

1
Q

How do limbs develop ?

A

Begins with limb buds

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2
Q

When do the limb buds for the upper limb appear?

A

Day 26

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3
Q

When do limb buds for lower limbs appear?

A

Day 28

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4
Q

What stimulates the somatic layer of lateral plate mesoderm to evaginate?

A

Somites

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5
Q

What forms a core of mesenchyme covered by surface ectoderm?

A

Somatic layer of lateral plate mesoderm

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6
Q

The mesenchyme directs the organization of myotomes to form structures

A 
Bones
Tendons 
Ligaments
Cartilage
Fascia 
Joints vessels
Dermis
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7
Q

What structures contribute to the formation of limbs?

A

Epidermis
Muscles
Nerves
Melanocytes

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8
Q

What embryonic structures are associated with epidermis, muscles, nerves, and melanocytes?

A 
Aer
Somites
Neuroectoderm
Neural crest 
Respectively
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9
Q

The limb buds grow mainly by what process?

A

Proliferation of mesenchyme

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10
Q

What genes regulate axes and patterning?

A

Hox genes

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11
Q

What forms at the apex of limb bud?

A

It thickens and forms apical ectodermal ridge

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12
Q

What does the Aer signal for?

A

Proliferation of the underlying mesenchyme

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13
Q

What is formed when mesenchymal cells aggregate at the posterior margin of the limb bud?

A

Zone of polarizing activity (ZPA)

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14
Q

What is the zone of polarizing activity responsible for?

A

Patterning of anterior/posterior axis

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15
Q

Retinoic acid

A

Shown to disrupt the development of limbs

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16
Q

When do the mesenchyme in the hand and foot plates condense to form digital rays?

A

6th and 7th week respectively

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17
Q

What induces the mesenchyme to form bones at the tips of digital rays?

A

Aer

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18
Q

When does chondrification centers appear ?

A

5th week

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19
Q

When do cartilaginous models of all limb bones appear?

A

6th week

20
Q

When does osteogenesis begin?

A

8th week

21
Q

When do the ossification of limb bones occur?

A

Begins toward the end of the embryonic period (week 8)

22
Q

What is the composition of epiphyses at the time of birth?

A

Shafts of the long bones are ossified but epiphyses are still cartilage

23
Q

How do the embryonic limbs obtain anatomical position?

A

Rotation of limbs
The upper limbs rotate laterally through 90 degrees on their long axis- extensors on the dorsal aspect of upper limb
The lower limb rotates medically almost 90 degrees - extensors on anterior aspect of lower limb

24
Q

How do the limbs get innervated?

A

Motor axons from spinal cord each the dorsal and ventral muscle masses during 5th week
Motor neurons grow first

25
Q

Dermatomes

A

Refer to segmental bands of skin innervated by spinal cord segment
As limbs elongate, the cutaneous distribution migrates along the limbs
There is a significant OVERLAP b/n dermatomes

26
Q

What is the blood supply to the limbs?

A

Dorsal intersegmental arteries that arise from dorsal aorta

Primordial vascular pattern consists of primary axial arteries and its branches

27
Q

What do the axial artery of the upper limb become!?

A

Brachial and continues as the common interosseous

The radial and ulnar arteries as secondary branches of the brachial

28
Q

What artery typical degenerates?

A

Median artery

29
Q

What becomes of the Axial artery of the lower limb?

A

Profunda femoris
Popliteal
Posterior tibial

30
Q

Which weeks are the most critical for limb development?

A

4th and 5th weeks

31
Q

What did thalidomide cause?

A

Many limb defects

The drug was used to tx morning sickness

32
Q

What usually causes limb defects?

A

Genetic factors

33
Q

Achondroplasia

A

Cause of dwarfism

Limbs are bowed and short
Disturbance of endochondral ossification at epiphyseal plates

34
Q

Thanatophoric dysplasia

A

Lethal skeletal dysplasia
Infants die soon after birth because of respiratory failure (muscles?ribs?)
Attributed to fibroblast growth factor receptor deficiency

35
Q

What is Amelia?

A

Absence of an entire limb

36
Q

Meromelia

A

Absence of a part of a limb

37
Q

What is cleft hand or foot?

A

Lobster claw deformity - fusion of digital rays
Absence of central digits - fusion of digital rays
Failure of digital rays to form-absence of digits

38
Q

Floating thumb

A

Absence of the metacarpal bone in the thumb

39
Q

Congenital absence of the radius

A

Radius failed to for,

Hand deviates laterally

40
Q

Brachydactyly

A

The digits are relatively short

Associated with short stature

41
Q

Polydactyly

A

Supernumery digits
Extra division of digital rays
Extra digit Usually useless

42
Q

Syndactyly

A

Defect is characterized by the fusion of the digital rays

Can be cutaneous (webbing of the digits) or Osseous (fusion of the bones)

43
Q

Congenital club foot

A

Talipes
Any defect involving the talus
results from abnormal orientation of the foot that prevents normal weight bearing
May be caused by environmental factor

44
Q

Congenital dislocation of the hip

A

Defect results from laxity of the joint capsule or underdevelopment of the acetabulum

45
Q

Genuine recurvatum

A

Congenital hyper extension of the knee

Returns to normal alignment without intervention

Musculoskeletal System (27 decks)

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