Embryology

Question 1

What weeks does limb development occur?

Answer 1

week 4 to 8

Question 2

What is activated at the start of limb development?

Answer 2

mesenchymal cells in the somatic lateral mesoderm

Question 3

What genes regulate the patterning of limbs?

Answer 3

homeobox

Question 4

What day does the upper limb and lower limb bud appear?

Answer 4

upper = day 24 
lower = 1-2 days later

Question 5

What HOXa genes are linked to the upper limb?

Answer 5

9-13

Question 6

How do limb buds elongate?

Answer 6

proliferation of mesenchyme

Question 7

Where do upper limb buds develop?

Answer 7

opposite caudal cervical segments

Question 8

Where do lower limb buds develop?

Answer 8

opposite lumbar and sacral segments

Question 9

What is formed at the end of each bud and how does this happen?

Answer 9

apical ectodermal ridge - AER

ectoderm thickens

Question 10

Describe the difference between mesenchyme adjacent and proximal to the AER

Answer 10

adjacent = undifferentiated, rapidly proliferating
proximal = differentiate into blood vessels and cartilage bone models

Question 11

In week 6 mesenchyme in hand plates form what?

Answer 11

digital rays

Question 12

What weeks are digital rays formed in the foot?

Answer 12

7

Question 13

What mediates apoptosis breakdown of interdigital regions?

Answer 13

bone morphogenetic proteins

Question 14

What bone does not undergo endochondral ossification? What type of ossification occurs?

Answer 14

clavicle - membranous

Question 15

Upper limb rotation

Answer 15

90 degrees laterally so extensors are lateral and posterior and thumb is lateral

Question 16

lower limb rotation

Answer 16

90 degrees medially so extensors medial and anterior and big toe is medial

Question 17

How is the dermatomal patterns of the limbs achieved?

Answer 17

in week 5 peripheral nerves from the limb plexus grow into mesenchyme of limbs

Question 18

amelia

Answer 18

total absence

Question 19

mecromelia

Answer 19

partial absence

Question 20

phocomelia

Answer 20

some long bones absent

Question 21

micromelia

Answer 21

all parts present but small

Question 22

inheritance of lobster claw feet

Answer 22

autosomal dominant

Question 23

When is the critical limb development period?

Answer 23

days 24-36

Question 24

polydactyly

Answer 24

presence of more than 5 digits on hands or feet

Question 25

describe the additional digit(s) in polydactyly

Answer 25

not fully formed and lacks muscular development

Question 26

cause of polydactyly

Answer 26

inherited or teratogen

Question 27

Is syndactyly more common in foot or hand?

Answer 27

foot

Question 28

cutaneous syndactyly

Answer 28

simple webbing

Question 29

osseous syndactyly

Answer 29

fusion of bones when notches between digital rays fail to develop

Question 30

action of Thalidomide

Answer 30

disrupts cell adhesion and angiogenesis

Question 31

some condition Thalidomide is now used to treat

Answer 31

cancer, AIDS, leprosy

Question 32

What is thalipes equinovarus?

Answer 32

club foot

Question 33

appearance of foot in club foot q

Answer 33

sole of foot turned medially and foot inverted

Question 34

cause of club foot

Answer 34

multifactorial

lack of space in womb

Question 35

Developmental dysplasia of hip

Answer 35

abnormal development of acetablum - breech

generalised joint laxity