1 - embryology of limbs

Question 1

when does limb development start?

Answer 1

begins near the end of 4th week

Question 2

how is limb development initiated?

Answer 2

Activation of mesenchymal cells in the somatic lateral mesoderm

Question 3

what genes regulate patterning during limb development?

Answer 3

homeobox genes

Question 4

when does upper limb bud appear?

Answer 4

day 24

Question 5

when does lower limb bud appear?

Answer 5

day 25/26

Question 6

what HOX genes are expressed in upper limb?

Answer 6

HOXd 9-13

Question 7

removal of which 2 HOX genes results in radius and ulna not forming?

Answer 7

HOXa and HOXd

Question 8

how do limb buds elongate?

Answer 8

by the proliferation of the mesenchyme

Question 9

where do upper limb buds develop?

Answer 9

opposite the lumbar and sacral segments

Question 10

how is the apical ectodermal ridge (AER) formed?

Answer 10

the ectoderm at the apex of each bud thickens

Question 11

what is the AER made of?

Answer 11

it is a multilayered epithelial structure

Question 12

what does the AER influence?

Answer 12

it exerts an inductive influence on the limb mesenchyme

Question 13

what cells are present in the mesenchyme adjacent to the AER?

Answer 13

undifferentiated, rapidly proliferating cells

Question 14

what cells are present in the mesenchyme proximal to the AER?

Answer 14

they differentiate into blood vessels and cartilage bone models

Question 15

what develops into hand and foot plates?

Answer 15

the distal ends of the limb buds

Question 16

what has occurred by the end of week 6?

Answer 16

mesenchymal tissue in hand plates has condensed to form digital rays

Question 17

what occurs in week 7?

Answer 17

digital rays are formed in the foot plates

Question 18

what is mediated by bone morphogenetic proteins?

Answer 18

apoptosis (which accounts for the breakdown in interdigital regions)

Question 19

when do the Cartilaginous precursors of the limb bones develop by chondrification within the mesoderm?

Answer 19

week 6

Question 20

what appears in weeks 8-12 in response to growth factors?

Answer 20

1y centres of ossification

Question 21

what type of ossification is present in all limb bones (except clavicle)?

Answer 21

endochondrial ossification

Question 22

what type of ossification is present in clavicle?

Answer 22

membranous

Question 23

how do upper limbs rotate?

Answer 23

90 degrees laterally

Question 24

how do lower limbs rotate?

Answer 24

90 degrees medially

Question 25

when do peripheral nerves grow and where do they originate?

Answer 25

week 5 - originate from the developing limb plexus into the mesenchyme of the limbs

Question 26

term for total absence of limbs at birth?

Answer 26

amelia

Question 27

term for partial absence of limbs at birth?

Answer 27

meromelia

Question 28

term for some long bone absence at birth?

Answer 28

phocomelia

Question 29

term for only small parts absent at birth?

Answer 29

micromelia

Question 30

how is lobster claw foot inherited?

Answer 30

autosomal dominant

Question 31

when is the critical period of limb development?

Answer 31

24-36 days after fertilisation

Question 32

polydactyly?

Answer 32

presence or more than 5 digits on hand/ foot

Question 33

what 2 mechanisms lead to polydactyly?

Answer 33

inherited or teratogen induced

Question 34

what is syndactyly?

Answer 34

webbing/fusions of bones

Question 35

cutaneous syndactyly?

Answer 35

simple webbing between the digits

Question 36

osseous syndactyly?

Answer 36

fusion of bones

Question 37

when does osseous syndactyly occur?

Answer 37

when notches between digital rays fail to develop

Question 38

what does thalidomide cause?

Answer 38

absence/ deformity of long bones - meromelia

Question 39

side effects of thalidomide?

Answer 39

intestinal atresia, cardiac anomalies

Question 40

what is congenital clubfoot AKA?

Answer 40

talipes equinovarus

Question 41

what is congenital clubfoot?

Answer 41

sole of foot is turned medially and the foot is inverted

Question 42

2 causes of clubfoot?

Answer 42

1 - multifactorial (genetics and environment), 2 - abnormal positioning of foetus' lower limb in utero

Question 43

2 causes of developmental dysplasia of the hip?

Answer 43

1 - abnormal development of acetabulum, 2 - generalised joint laxity

Question 44

does syndactyly occur more in hand/foot?

Answer 44

in feet more often