Application of Medical Embryology

3D embryology

Lateral folding

  • Converts the open coelom into a closed cavity
    • Creates thoracic and abdominal cavity
    • Closes fore and hindgut (midgut is last to close)

Cranial folding

  • Forms the foregut and defines the thoracic cavity
  • Developing heart tube displaced into thoracic cavity

Caudal folding

  • Cloacal membrane and connecting stalk are displaced ventrally alongside neck of yolk sac
  • Forms hindgut, anus and umbilical cord

Heart development

  • Heart begins to develop at week 4
  • Cardiac progenitor cells migrate through the primitive streak into the visceral layer of lateral plate mesoderm
  • Heart tube formed through craniocaudal and lateral folding

Normal atrial septation

  • 2 septa - primum (30 days) and secundum (33 days)
  • Communication between right and left atria until birth - foramen ovale
    • Valve of foramen ovale closed by increased pressure in left atrium (caused by crying and first breath) and initially decreasing pressure in right atrium (caused by constriction of umbilical vessels) → interatrial septum

Normal ventricular septation

  • Muscular portion grows upwards from wall of expanding ventricle
  • Membranous portion - growth of tissue from endocardial cushions
  • Ventricular septation closely linked to septation of outflow tract

Transposition of the great vessels

  • Aorta emerges from the right ventricle and pulmonary artery arises from the left ventricle

Abnormalities in heat development

  • Embryo most at risk of defects weeks 3-8
  • Atrial septal defect (ASD): incomplete closure of the embryonic foramen ovale in the septum
  • Ventricular septal defect (VSD): incomplete closure of interventricular septum
  • Tetralogy of Fallot: pulmonary stenosis, right ventricular hypertrophy, VSD, overriding aorta
    • Can be associated with Down’s syndrome