Development of Limbs

Question 1

When does the development of limbs begin?

Answer 1

Near the end of the 4th week

Question 2

What is activated in the somatic lateral mesoderm?

Answer 2

Mesenchymal cells

Question 3

What regulates patterning?

Answer 3

Homeoxbox genes

Question 4

When do the upper limb buds apper?

Answer 4

Day 24

Question 5

When do the lower limb buds appear

Answer 5

1 to 2 days after the upper limb ones

Question 6

Explain HOX genes

Answer 6

Regionally expressed in limbs and determine which skeletal element formed

HOX gene expression results from a combination of the expression of SHH, FGF’s and WNT-7a

Question 7

What HOX genes form the upper limb?

Answer 7

HOXd 9-13

Question 8

What happens if HOXa 11 and HOXd 11 are removed?

Answer 8

Radius and ulna do not form

Question 9

What are limb buds elongated by?

Answer 9

Proliferation of mesenchyme

Question 10

What do upper limbs buds develop opposite?

Answer 10

The caudal cervical segments

Question 11

What do the lower limb buds form opposite?

Answer 11

The lumbar and sacral segments

Question 12

What happens at the apex of each limb bud?

Answer 12

Ectoderm thickens to form and apical ectodermal ridge

Question 13

What is AER restricted to?

Answer 13

End of limb bud

Question 14

What is the apical ectodermal ridge?

Answer 14

Multilayered epitherlial structre

Exerts an inductive influence on the limb mesenchyme

Question 15

What does the mesenchyme ajacent to the AER consist of?

Answer 15

Undifferentiated rapidly proliferating cells

Question 16

What do mesenchymal cells proximal to the apical ectodermal ridge differentiate into?

Answer 16

Blood vessels and cartilage bone models

Question 17

What do the distal ends of the limb buds flatten into?

Answer 17

Paddle-like hand plates and flipper- like foot plates

Question 18

What has happened by the end of the 6th week to mesenchymal tissue in hand plates?

Answer 18

Condensed to form digital rays

Question 19

What happens during the 7th week to foot plates?

Answer 19

Digital rays are formed in the foot plates

Question 20

What does the development of the hands look like?

Answer 20

Question 21

What does the development of the feet like?

Answer 21

Question 22

What is programmed cell death responsible for?

Answer 22

The tissue breakdown in the interdigital regions –mediated by bone morphogenetic proteins

Question 23

What do cartilagionous precursors of the limb bones develop by?

Answer 23

Chondrification within the mesoderm in the 6th week

Question 24

When do primary centres of ossification appear?

Answer 24

Weeks 8 to 12 in response to growth factors

Question 25

What occurs in all bones in limbs development except the clavicle?

Answer 25

Enodochrial ossification. Clavicle is membranous

Question 26

What is limb rotation like?

Answer 26

Upper limbs and lower limbs rotate

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

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

Question 27

Upper limb dermatomal development. Draw it!

Answer 27

Question 28

Lower limb dermatomal development. Draw it!

Answer 28

Question 29

What grows into the mesenchyme of the limbs?

Answer 29

During the 5th week, peripheral nerves grow from the developing limb plexus

(brachial and lumbosacral) into the mesenchyme of the limbs

Question 30

What is total absence of limbs called?

Answer 30

Amelia

Question 31

What is partial absence of limbs called?

Answer 31

Meromelia

Question 32

What is some long bones absence called?

Answer 32

Phocomelia

Question 33

What is it called with all long bones present but small?

Answer 33

Micromelia

Question 34

What is the inheritance pattern of lobster claw foot?

Answer 34

Autosomal dominant triat

Question 35

What is the critical period of limb development?

Answer 35

24-36 days after fertilization

Question 36

What is polydactyly?

Answer 36

Presence of more than 5 digits on hand or feet

Extra digit is incompletely formed and lacks muscular

development

May be inherited or teratogen induced

Question 37

What is syndactyly?

Answer 37

Common birth defect of the hand and foot

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

More frequent in the foot than in the hand

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

Question 38

What was thalidomide used as?

Answer 38

1957-1962 used as a sleeping tablet and anti-nauseant

Question 39

What does thalidomide cause?

Answer 39

Absence or deformity of long bones (intestinal atresia and cardiac anomalies)

‘Sensitive’ period 4-8wks

Acts by disrupting cell adhesion and angiogenesis

Question 40

What is thalidomide used for?

Answer 40

Used to help cancer, leprosy and AIDS patients

Question 41

What is congenital clubfoot called?

Answer 41

Talipes Equinovarus

Question 42

What does talipes equinovarus look like?

Answer 42

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

Question 43

What is the cause of congenital clubfoot?

Answer 43

Multifactorial (genetic and environmental factors)

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

Question 44

What percentage of patients with congenital disloavtion of the hip have abnormal develop of acetabulum?

Answer 44

15%

Question 45

When is abnormal develop of the acetabulum common?

Answer 45

Common after breech(buttocks) deliveries -? Breech posture during late part of pregnency (abnormal development of acetabulum and head of femur)

Question 46

What is generalised joint laxity?

Answer 46

Multifactoril

Associated with congenital disloaction of hip

Question 47

You’re doing really well :)

Answer 47

Ok