Session 1: Prenatal limb development and congenital abnormalities

Question 1

When do the limb buds appear?

Answer 1

At the end of the 4th week

Lower limb 2 days behind upper

Question 2

Describe the structure of the limb buds

Answer 2

Core of proliferating mesenchymal cells (Mesenchymal stem cells, or MSCs, are multipotent stromal cells that can differentiate into a variety of cell types, including: osteoblasts (bone cells), chondrocytes (cartilage cells), myocytes (muscle cells) and adipocytes (fat cells).)

with an ectoderm covering (outside layer)

Question 3

What is the apical ectodermal ridge?

Answer 3

Thickened ectoderm at apex of limb bud

Limb bud outgrowth orchestration

Proximal to distal

AER keeps mesenchyme undifferentiated and regresses

Question 4

What is the zone of polarising activity?

Answer 4

Generates limb asymmetry (radius and ulna)

Posterior base of limb bud

Controls patterning and maintains AER

Question 5

What are digital rays?

Answer 5

Mesenchyme condensations within plates

Cartilaginous models of digit bones

Question 6

How does the tissue between digits disappear?

Answer 6

Apoptosis

AER breaks up and only stays on the tips of the digital rays

Question 7

What is syndactyly?

Answer 7

Digit fusion

CT or bones

Question 8

What is polydactyly?

Answer 8

Extra digits

Question 9

What is amelia?

Answer 9

Absence of a limb

Question 10

What is meromelia?

Answer 10

Partial absence of one or more limb structures

Question 11

What is phocomelia?

Answer 11

“Seal”

Limbs attached close to body

Thalidomide

Malformation of limbs

Question 12

State three ways in which limb development can be affected

Answer 12

Error in morphogenesis coordination

Deformation - constriction bands - fibrous amniotic bands (clubfoot - The affected foot appears to have been rotated internally at the ankle)

External agent: thalidomide, TORCH (toxoplasmosis, other (syphilis, varicella-zoster, parvovirus B19), rubella, cytomegalovirus, herpes

Question 13

How are the limb buds innervated?

Answer 13

Caudal C spine - upper

Lumbosacral - lower

Question 14

Describe muscle development in the embryo’s limbs

Answer 14

Myogenic precursors migrate from somites

2 common muscle masses: ventral flexor, dorsal extensor

Muscles then split from common masses

Question 15

Describe the rotation of the embryo’s limbs

Answer 15

Extend ventrally

Elongate and rotate

Upper: laterally

Lower: medially

Question 16

What is the difference between cutaneous syndactyly and osseous syndactyly?

Answer 16

Just connective tissue

Bones joined too

Question 17

What is the structural defect underlying congenital dislocation of the hip?

Answer 17

Complete or partial displacement of femoral head from acetabulum

Ball loose in socket

The presence of the spherical femoral head within the acetabulum is critical for stimulating normal development of the acetabulum.

Shallow acetabulum, ligamentous laxity

Question 18

Why is CHD associated with breech delivery?

Answer 18

Mechanical forces on the hips and pelvis

Question 19

Describe the movements of the thumb

Answer 19

See image

Question 20

What does the axillary sheath contain?

Answer 20

fibrous sheath that encloses the first portion of the axillary artery, together with the brachial plexus

Question 21

Describe the walls of the axilla

Answer 21

Lateral wall – Formed by intertubercular groove of the humerus.

Medial wall – Consists of the serratus anterior and the thoracic wall (ribs and intercostal muscles).

Anterior wall – Contains the pectoralis major and the underlying pectoralis minor and the subclavius muscles.

Posterior wall – Formed by the subscapularis, teres major and latissimus dorsi.

Question 22

Describe the three sections of the axillary artery

Answer 22

Its origin is at the lateral margin of the first rib, before which it is called the subclavian artery.

After passing the lower margin of teres major it becomes the brachial artery.