Embryology Flashcards

1
Q

How does limb development begin in utero

A

Begins near end of 4th week.
ACtivation of mesenchymal cells in the somatic layer of the mesoderm
Homeobox genes regulate patterning

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2
Q

When do the limb buds appear?

A

Day 24 upper limb bud

1-2 days later lower limb bud appears

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3
Q

What are HOX genes

A

genes that determine which skeletal elements are formed

Hox9-13 genes reposnible for forming upper limg. Remove Hoxa 11 and Hoxd 11 and the radius and ulna do not form

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4
Q

How do the limb buds develop?

A

Limb buds elongate by the proliferation of the mesenchyme

Upper limb buds develop opposite the caudal cervical segments

Lower limb buds form opposite the lumbar and sacral segments

At the apex of each bud the ectoderm thickens to form an apical ectodermal ridge (AER)

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5
Q

What is the AER

A

restricted to the end of the limb bud, multilayered epithelial structure. Exerts an inductive influence of the limb mesenchyme

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6
Q

How does the AER influence the structures around

A

Mesenchyme adjacent to the AER consists of undifferntiated rapidly proliferating cells.

Mesenchymal cells proximal to it differentiate into blood vessels and cartilage bone models

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7
Q

Describe the process of limb development

What causes the breakdown of the tissue to form digit development

A
Limb buds
Paddle shaped plates
Digital rays
Notches between rays
Webbed fingers and toes
Seperate digits of the fingers and toes

occurs between the 4th and 8th weeks

Programmed cell death occurs to break down tissues that arent needed. Mediated by bone morphogenetic proteins

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8
Q

What are the final stages of limb development

A

Cartilaginous precursors of the limb bones develop by chondirfication within the mesoderm

Primary centres of ossification appear in weeks 8-12 in response to growth factors

Endochondrial ossification for all limb bones except the clavicle

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9
Q

How do the limbs originally develop

A

Upper limbs rotate 90 degrees laterally so that extensors are in lateral positions

Lower limbs rotate 90 degrees medially so that the extensors are on the anterior surface

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10
Q

What is:

Amelia
meromelia
phocomelia
misromelia
polydactly
A
Amelia- total absence
meromelia- Partial absence
phocomelia- absence of long bones
micromelia- all parts present but small
prescence of more than 5 digits on the nads or feet
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11
Q

Why does lobster claw foot

A

Autosomal dominant trait, critical period of limb development 24-36 after fertilization

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12
Q

What is syndactyly

A

Common birth defect of hand or foot. Can cause simple webbing or range to fusion of the digital bones.

more common in the foot

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13
Q

Explain congenital clubfoot

A

Sole of foot is tuned medially and foot is inverted.
Can be cuased by many factor e.g. genetics and environemnt
Abnormal positioning or restricted movement of the fetus’ lower limb in utero

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14
Q

Explain developmental dysplasia of the hip

A

Abnormal development of the acetabulum
15% of infants with congenital dislocation of the hip
Common after breech deliveries.

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