Lecture 3 Embryology

Question 1

What day do the upper limb buds appear?

Answer 1

Day 24

Question 2

What day do the lower limb buds appear

Answer 2

1-2 days after upper limb buds

Question 3

How do limb buds elongate

Answer 3

By proliferation of mesenchyme

Question 4

Where do upper limb buds develop

Answer 4

Opposite caudal cervical segments

Question 5

Where do lower limb buds form

Answer 5

Opposite the lumbar and sacra segments

Question 6

At the apex of each bud the ectoderm thickens to form what?

Answer 6

Apical ectodermal ridge (AER)

Question 7

What is the Apical ectodermal ridge (AER)?

Answer 7

Multilayered epithelial structure that exerts an inductive influence on the limb mesenchyme

Question 8

At what week do mesenchymal tissue in hand plates condense to form digital rays

Answer 8

6th week

Question 9

What week do digital rays formed in the foot plates

Answer 9

7th week

Question 10

What time period do the development of hands and feet occur

Answer 10

4th to 8th week

Question 11

What is responsible for the tissue breakdown in the interdigital regions

Answer 11

Apoptosis

Mediated by bone morphogenetic proteins

Question 12

What is the final stage of limb development

Answer 12

Chondrification

Endochondral ossification

Question 13

What direction do upper limbs rotate?

Answer 13

Laterally so that the extensors are on the lateral and posterior surface

Question 14

What direction do lower limbs rotate

Answer 14

Medially so that the extensors are on the anterior surface

Question 15

At what week does the dermatomal patterns of the limbs develop

Answer 15

5th week

Question 16

Name birth defects of the limbs

Answer 16

Amelia- total absence
Meromelia- Partial absence
Phocomelia- Some long bone absence
Micromelia- all parts present but small

Question 17

Define Polydactyly

Answer 17

Presence of more than 5 digits on the hands or feet

Question 18

Define Cutaneous Syndactyly

Answer 18

Simple webbing between the digits

Question 19

Define Osseous Syndactyly

Answer 19

Fusion of the bones

Question 20

What is club foot

Answer 20

Sole of foot is turned medially and foot is inverted

Question 21

What are the causes of club foot

Answer 21

o	Multifactorial (genetic and environmental factors)
o	Abnormal positioning or restricted movement of the foetus’s lower limb in the utero – Evidence is inconclusive

Question 22

Causes of dysplasia of the hip

Answer 22

Breech delivery
Multifactorial
Associated with congenital dislocation of hip