Embryology

Question 1

When do the limbs start to develop?

what is there activation of?

Answer 1

end of 4th week

- mesenchymal cells in the somatic lateral mesoderm

Question 2

What appears at day 24

Answer 2

Upper limb bud appear

Question 3

What genes regulate patterning

Answer 3

Homebox

Question 4

What genes are expressed in the upper limb

Answer 4

HOXd 9-13

Question 5

HOX genes determine

Answer 5

which skeletal element formed

Question 6

If you remove HOXa 11 and HOXd 11 what doesn’t form?

Answer 6

radius and ulna

Question 7

Limb buds elongate by the proliferation of

Answer 7

Mesenchyme

Question 8

Upper limb buds develop?

Answer 8

opposite the caudal cervical segments

Question 9

Lower limb buds form opposite the ?

Answer 9

lumbar and sacral segments

Question 10

What happens at the apex of each bud

Answer 10

ectoderm thickens to form an apical ectodermal ridge (AER)

Question 11

Apical Ectodermal Ridge (AER) - features

Answer 11

restricted to end of limb bud
Multilayered epithelial structure

Exerts an inductive influence on the limb mesenchyme

The mesenchyme adjacent to the AER consits of undifferentiated, rapidly proliferating cells

whereas mesenchymal cells proximal to it differentiate into blood vessels and cartilage bone

Question 12

Development of hand & foot plates

Answer 12

The distal ends of the limb buds flatten into paddle-like hand plates and flipper- like foot plates

By the end of 6th week, mesenchymal tissue in hand plates has condensed to form digital rays

During the 7th week digital rays are formed in the foot plates

Question 13

Development of hands and feet between the ?

Answer 13

4th and 8th weeks

Question 14

What is Programmed cell death (apoptosis) is responsible for

Answer 14

tissue breakdown in the

interdigital regions –mediated by bone morphogenetic proteins

Question 15

Final stages of limb development - how do Cartilaginous precursors of the limb bones develop ?

Answer 15

chondrification within the mesoderm in the 6th week

Question 16

Primary centres of ossification appear in ?

Answer 16

weeks 8 to 12 in response to growth factors

Question 17

What ossification takes place for all limb bones except the clavicle

Answer 17

Endochondrial

Question 18

How do the upper and Lower limbs rotate and what direction/why?

Answer 18

Upper limbs rotate 90 laterally so that extensors are on the lateral and posterior surfaces (and the thumb is lateral)

Lower limbs rotate 90 medially so that the extensors are on the anterior surface (and the big toe is medial)

Question 19

What happens during the 5th week

Answer 19

peripheral nerves grow from the developing limb plexus

(brachial and lumbosacral) into the mesenchyme of the limbs

Question 20

Birth Defects of Limbs - total absence vs partial absence

Answer 20

(amelia), partial absence (meromelia)

Question 21

Some long bone absence

Answer 21

phocomelia

Question 22

All parts present but small

Answer 22

micromelia)

Question 23

lobster claw can be inherited as a

Answer 23

autosomal dominant trait

Question 24

Critical period of limb development: is?

Answer 24

24-36 days after fertilization

Question 25

What is Polydactyly

Answer 25

Presence of more than 5 digits on the hands or feet

Extra digit is incompletely formed and lacks muscular
development

May be inherited or teratogen induced

Question 26

What is Syndactyly

Cutaneous vs osseous

Answer 26

Common birth defect of the hand

Cutaneous Syndactyly (simple webbing between the digits) is
     -  a common limb defect

Osseous Syndactyly (fusion of bones) occurs when notches between the digital rays
     fail to develop

Question 27

Congenital Clubfoot also known as?

Answer 27

TALIPES EQUINOVARUS (Club foot

Question 28

What is the features of club foot

Answer 28

Sole of the foot is turned medially and the foot is inverted

Question 29

What causes club foot (2)

Answer 29

Multifactorial (genetic and environmental factors)

2) Abnormal positioning or restricted movement of the
fetus’s lower limb in the utero – Evidence is inconclusive

Question 30

Developmental Dysplasia of the Hip due to?

Answer 30

Abnormal development of acetabulum

Question 31

When is dysplasia of the hip common

Answer 31

breech(buttocks) deliveries -? Breech posture during late part of pregnency (abnormal development of acetabulum

Question 32

2 features of Generalized joint laxity

Answer 32

Multifactorial

Associated with congenital dislocation of hip