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Heart DevelopmentDr. NimirObjectives: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 endocardiumMyoepicardial mentle myocardium, epicardiumCardiac 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 ventricle4. Partitioning of Heart Chambers4.1 Division of atrioventricular canal Subendocardial tissue 2 endocardial cushions fuse right and left canals

Formation of atrioventricular valves4.2 Partitioning of primitive atrium1) Septum primum endocardial cushions foramen primum.

2) Septum primum absorbed foramen secundum foramen primum closing3) Septum secundum cover the foramen secundum foramen ovale

4) Blood from right to left atrium

foramen ovale4.3 Development of sinus venosusRight 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 ventricle1) 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 Truncal ridges + Bulbar ridges aorticopulmonary septum

2) Aorticopulmonary septum spiral course pulmonary trunk right ventricleaorta left ventricle

3) Truncus swellings hollowed out at upper surface semilunar valves5. Circulation before and after Birth5.1 Circulation before birth

Placental circulation: umbilical A. & V.ductus venosusforamen ovaleductus arteriosus

5.2 Changes after birthUmbilical arteries lateral umbilical ligamentsUmbilical vein ligamentum teres hepatisDuctus venosus venous ligamentDuctus arteriosus arterial ligamentForamen 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 FallotUnequal division of conus cordis; 4 defects: pulmonary stenosis, overriding aorta, ventricular septal defect, hypertrophy of right ventricle; Causing cyanosis.

6.4 Persistent truncus arteriosusTruncoconal 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 vesselsTruncoconal 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 arteriosusDuctus arteriosus fails to be closed after birth;Isolated or combined with other defects.

6.7 Tricuspid atresiaAbsence or fusion of tricuspid valves;Patent oval foramen & ventricular septal defect;Underdeveloped right ventricle6.8 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 stenosisAortic valves are fused for variable distance;Aorta, left ventricle, left atrium underdeveloped;Accompanied by patent ductus arteriosus.

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