Embryology

Question 1

outline the early stages of limb development…

Answer 1

starts at w4, activation of mesenchymal cells in the somatic lateral plate mesoderm, homeobox genes regulate patterning, at day 24 upper limbs appear, 1-2 days later lower limbs appear

Question 2

which HOXd genes pattern the upper limb?

Answer 2

HOXd 9-13, remove HOXa 11 and HOXd 11 and the radius and ulna do not form.

Question 3

limb buds elongate because of the proliferation of the…

Answer 3

Mesenchyme

Question 4

At the apex of each bud the ectoderm thickens to form an…

Answer 4

apical ectodermal ridge (AER)

Question 5

what is the AER?

Answer 5

restricted to the end of the limb bud, multilayered epithelial structure, Exerts an inductive influence on the limb mesenchyme

Question 6

The mesenchyme adjacent to the AER consits of

Answer 6

undifferentiated, rapidly proliferating cells

Question 7

whereas mesenchymal cells proximal to it differentiate into

Answer 7

blood vessels and cartilage bone models

Question 8

how does the development of hand and foot plates occur?

Answer 8

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 9

what does bone morphogenetic proteins mediate?

Answer 9

Programmed cell death (apoptosis) is responsible for the tissue breakdown in the interdigital regions

Question 10

what are the final stages of limb development?

Answer 10

Cartilaginous precursors of the limb bones develop by chondrification within the mesoderm in the 6th week, Primary centres of ossification appear in weeks 8 to 12 in response to growth factors, Endochondrial ossification for all limb bones except the clavicle (membranous). then the limbs rotate 90 degrees.

Question 11

dermatome development…

Answer 11

During the 5th week, peripheral nerves grow from the developing limb plexus, (brachial and lumbosacral) into the mesenchyme of the limbs

Question 12

what is amelia?

Answer 12

total absence of limb

Question 13

what is meromelia?

Answer 13

partial absense

Question 14

what is phocomelia?

Answer 14

some long bone

Question 15

what is micromelia?

Answer 15

all parts present but the limb is small

Question 16

when Is the period of criticsal limb development?

Answer 16

24-35 days after fertilisation.

Question 17

what is polydactyly?

Answer 17

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 18

what is syndactyly?

Answer 18

Common birth defect of the hand or 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 19

Thalomide issues?

Answer 19

1957-1962 used as a sleeping tablet and anti-nauseant = partial absence (meromelia) or deformity of long bones (intestinal atresia and cardiac anomalies), Acts by disrupting cell adhesion and angiogenesis, Now used to help cancer, leprosy and AIDS patients

Question 20

Congenital club foot…

Answer 20

Also known as TALIPES EQUINOVARUS (Club foot), Relatively common birth defect, Sole of the foot is turned medially and the foot is inverted. Cause: 1) Multifactorial (genetic and environmental factors), 2) ? Abnormal positioning or restricted movement of the fetus’s lower limb in the utero – Evidence is inconclusive.

Question 21

developmental dysplasia of the hip…

Answer 21

Abnormal development of acetabulum - 15% of infants with congenital dislocation of the hip, Common after breech(buttocks) deliveries -? Breech posture during late part of pregnency (abnormal development of acetabulum and head of femur). Generalized joint laxity, Multifactorial, Associated with congenital dislocation of hip

Question 22

what mesoderm forms cartilage, bone, deeo fascia and ligaments?

Answer 22

parietal laterl plate mesoderm

Question 23

what mesoderm forms catilage, bone, deepfascia, ligaments?

Answer 23

Parietal lateral plate mesoderm

Question 24

Column of mesodermal condensation appears along long axis of bud during

Answer 24

week 5

Question 25

when does condrification of cartilaginous precursors occur?

Answer 25

week 6