Heart Development

Dr. Nimir

• Objectives:

• Understand early development of blood vessels.

• Basic understanding of the early stages of heart development.

• Describe the formation and position of the heart tube.

• Discus the development of sinus venosus.

• Describe partioning by septa and chambers formation.

• Discus congenital malformations.

• Gain knowledge of fetal circulation.

1. Development of Early Blood Vessels1.1 Yolk sac → blood islands → endothelia → vessels primitive blood cells.

1.2 Chorion, body stalk, embryonic body → blood vessels → 3 separate circulations: vitelline, chorionic, and intraembryonic.

2. Development of Primitive Heart Tube2.1 Primordium: Cardiogenic area → •Intraembryonic coelom → pericardial coelom; •2 lateral cardiogenic plates →endocardial heart tubes.

2.2 Primitive heart tube1) Lateral fold: 2 heart tubes → single heart tube.

2) Head fold: pericardial coelom → ventral to heart tube ↘caudal to oropharyngeal membrane

3) Wall of primitive heart tube •Endocardial heart tube → endocardium•Myoepicardial mentle → myocardium, epicardium•Cardiac jelly → subendocardial tissue

3. Formation of Heart Loop

3.1 Heart tube → bulbus cordis, ventricle, atrium → truncus arteriosus, conus cordis, ventricle, atrium, sinus venosus

3.2 Bulboventricular portion → bulboventricular loop → cephalic portion bends ventrally, caudally and slightly to the right

3.3 Atrium → dorsocranially and bulges laterally on each side of bulbus

3.4 Proximal part of bulbus → primitive right ventricle

4. Partitioning of Heart Chambers

4.1 Division of atrioventricular canal

Subendocardial tissue → 2 endocardial cushions → fuse → right and left canals

Formation of atrioventricular valves

4.2 Partitioning of primitive atrium

1) Septum primum → endocardial cushions → foramen primum.

2) Septum primum absorbed → foramen secundum → foramen primum closing

3) Septum secundum → cover the foramen secundum → foramen ovale

4) Blood from right to left atriumforamen ovale

4.3 Development of sinus venosus

1) Right horn enlarges (due to left-to-right shunts of blood in venous system)

•Sinus-atrial orifice → right;

•Receives sup. and inf. vena cava;

•Right horn → right atrium (smooth walled part).

2) Left horn degenerates → coronary sinus, oblique vein of left atrium;

•Pulmonary vein and its branches → left atrium (smooth walled part)

4.4 Partitioning of the primitive ventricle

1) Apical ventricle wall → muscular interventricular septum → interventricular foramen

2) Endocardial cushion, right and left bulbar ridges → membranous interventricular septum → interventricular foramen closed

4.5 Division of truncus and bulbus 1) Truncal ridges + Bulbar ridges →aorticopulmonary septum

2) Aorticopulmonary septum → spiral course → • pulmonary trunk → right ventricle• aorta → left ventricle

3) Truncus swellings → hollowed out at upper surface → semilunar valves

5. Circulation before and after Birth

5.1 Circulation before birth

•Placental circulation: umbilical A. & V.

•ductus venosus

•foramen ovale

•ductus arteriosus

5.2 Changes after birth

•Umbilical arteries → lateral umbilical ligaments

•Umbilical vein → ligamentum teres hepatis

•Ductus venosus → venous ligament

•Ductus arteriosus → arterial ligament

•Foramen ovale → oval fossa

6. Congenital Malformations

6.1 Atrial septal defect

•Excessive resorption of the septum primum;

•Inadequate development of the septum secundum.

6.2 Ventricular septal defect

•Defect of the membranous septum, isolated or associated with other abnormalities.

6.3 Tetralogy of Fallot

•Unequal division of conus cordis;

•4 defects: pulmonary stenosis, overriding aorta, ventricular septal defect, hypertrophy of right ventricle;

•Causing cyanosis.

6.4 Persistent truncus arteriosus

•Truncoconal ridges fail to fuse and descend;

•Truncus overrides both ventricles;

•Accompanied by ventricular septal defect;

•Cyanosis, blood to lungs increased.

6.5 Transposition of great vessels

•Truncoconal septum failing to follow its spiral course and descending straight downward;

•Aorta originates from right ventricle, pulmonary artery from left;

•Usually combined with patent ductus arteriosus.

6.6 Patent ductus arteriosus

•Ductus arteriosus fails to be closed after birth;

•Isolated or combined with other defects.

6.7 Tricuspid atresia

•Absence or fusion of tricuspid valves;

•Patent oval foramen & ventricular septal defect;

•Underdeveloped right ventricle

6.8 Pulmonary valvular atresia (or stenosis)

•Pulmonary valves are fused for variable distance;

•Hypoplastic right heart;

•Patent oval foramen and patent ductus arteriosus.

6.9 Aortic valvular atresia and stenosis

•Aortic valves are fused for variable distance;

•Aorta, left ventricle, left atrium underdeveloped;

•Accompanied by patent ductus arteriosus.

Thank You