Embryology Flashcards

1
Q

When does limb bud development begin?

A

End of week 4

Specifically the upper limb bud forms around day 24 and the lower 1-2 days later

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2
Q

What embryonic cells give rise to the limb buds?

A

Lateral plate somatic mesoderm

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3
Q

What regulates limb development?

A

Homeobox (HOX) genes

They determine what skeletal element is formed

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4
Q

What happens to the apex of each limb bud?

A

Surface ectoderm thickens to form a the Apical Ectodermal Ridge (AER)

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5
Q

What is the function of the AER?

A

It induces the mesenchyme to proliferate

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6
Q

What happens to the mesenchyme of the limb bud as it elongateS?

A

Mesenchyme adjacent to AER is mainly undifferentiated rapidly proliferating cells.

But more proximal mesenchyme differentiates into vessels and cartilage bone models

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7
Q

How do the hands/feet first form?

A

The distal limb buds flatten into paddle-like hand and foot plates

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8
Q

What happens after hand/foor plates are formed?

A

Mesenchyme condenses to form digital rays

  • > Then notches appear between them
  • > Webbed fingers/toes
  • > Seperate digits
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9
Q

When do digital rays form?

A

end of week 6 for hand plates and week 7 for foot plates

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10
Q

When are separate digits formed?

A

by the end of week 8

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11
Q

How is the tissue between individual digits removed?

A

Apoptosis mediated by Bone Morphogenetic Proteins

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12
Q

When do cartilage bone-precursors start to form and how?

A

in week 6 by chondrification

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13
Q

When does cartilage ossify into bone?

A

weeks 8-12 in response to growth factors

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14
Q

What type of ossification do limb bones undergo?

A

Endochondral

Except for the clavicle which ossifies by membranous ossification

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15
Q

How do limbs rotate and what is the result of this?

A

Upper limbs rotate 90* laterally
Lower Limbs rotate 90* medially

Hence the upper limb flexors are anterior and the lower are posterior

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16
Q

At what point do peripheral nerves start to grow into the limb buds?

A

They develop from the brachial/lumbosacral plexuses during wk 5

17
Q

Whens the critical period for MSK birth defects?

A

24-36 days

18
Q

What do we call absent bones?

A

Total - Amelia
Partial - Meromelia
Long bones - Phocomelia

19
Q

What do we call it when the bones are small?

A

Micromelia

20
Q

What do we call it if you have too many digits?

A

Polydactyly

The extra digit usually lacks muscle and is incomplete

21
Q

What causes polydactyly?

A

Its inherited or teratogen induced

22
Q

What do we call webbed fingers?

A

Cutaneous Syndactyly

23
Q

What is the other type of syndactyly?

A

Osseous Syndactyly

Where the actual digit bones are fused

Much more common in feet

24
Q

What causes osseous syndactyly?

A

Failure of notches between digital rays to develop

25
Q

When and for what was thalidomide used?

A

As an anti-nausent and sleeping pill from 1957-62

26
Q

What does thalidomide cause in babies?

A

Absent or deformed long bones
Intestinal Atresia
Cardiac Abdnormalities

By disrupting cell adhesion and angiogenesis

27
Q

When is thalidomide most sensitive for babies?

A

4-8wks gestation

28
Q

What do we use thalidomide for today?

A

Cancer
Leprosy
AIDS

29
Q

What is Clubfoot called, and what is it?

A

Talipes Equinovarus

The sole of the foot is turned medially and inverted

30
Q

How do we cause clubfoot?

A

Multifactorial

Genetic and environmental

31
Q

What causes developmental dysplasia of the hip?

A

Either a multifactoral Generalised Joint Laxity
Or an Abnormal Acetabulum which is common after breech deliveries

Both are associated with congenital dislocation of the hip