Development of the Heart

Cardiovascular System: Early Development

The cardiovascular system forms first in an embryo because simple diffusion can no longer supply nutrients or remove wastes as the embryo rapidly grows

Cardiovascular System: Early Development: Dangers

Any disruptions in the development of cardiovascular system can result in heart disorders present at birth

18-19 Days of Germination

The embryonic human heart begins to form from the mesoderm (middle germ layer) around 18 to 19 days after fertilization

Cardiogenic Mesenchyme

In the head end of the embryo, the heart develops from a group of mesodermal cells called the cardiogenic mesenchyme

Cardiogenic Cords

Signals from the underlying endoderm cause mesoderm in the cardiogenic mesenchyme to form two elongated strands called cardiogenic cords.

Heart Primordial Tubes

After the cardiogenic cords form, they develop a hollow center and then become known as heart primordial tubes.

Heart Tube

During lateral folding of the embryo, the two paired heart tubes fuse into one heart tube on day 21 after fertilization.

22 Days of Germination

The heart tube develops into five key regions that eventually form the distinct structures of the adult heart to begin pumping blood from tail to head: sinus venosus → primitive atrium → primitive ventricle → bulbus cordis → truncus arteriosus.

22 Days of Germination: Sinus Venosus

The sinus venosus develops into part of the right atrium (posterior wall), coronary sinus, and sinoatrial (SA) node.

22 Days of Germination: Primitive Atrium

The primitive atrium develops into part of the right atrium (anterior wall), right auricle, left atrium’s anterior wall, and the left auricle

22 Days of Germination: Primitive Ventricle

The primitive ventricle gives rise to the left ventricle.

22 Days of Germination: Bulbus Cordis

The bulbus cordis develops into the right ventricle.

22 Days of Germination: Truncus Arteriosus

The truncus arteriosus gives rise to the ascending aorta and pulmonary trunk.

23 Days of Germination

The heart tube elongates and begins to loop and fold, first forming a U-shape and then an S-shape because the bulbus cordis and primitive ventricle grow faster than the other regions.

28 Days of Germination

The heart’s looping is complete and repositions the primitive atria and ventricles into their adult locations; the remainder of heart development then remodel and develop septa and valves to form the four-chambered heart.

28 Days of Germination: Endocardial Cushions

Endocardial cushions are mesodermal thickenings in the heart wall that fuse to divide the single atrioventricular canal into separate right and left canals— while the interatrial septum grows toward the fused cushions.

28 Days of Germination: Foramen Ovale

The interatrial septum and endocardial cushions unite to form the foramen ovale, which allows most blood to flow from the right atrium to the left atrium before birth; it normally closes after birth, leaving the fossa ovalis as its remnant.

28 Days of Germination: Heart Septation and Valve Formation

The interventricular septum divides the ventricles into a right and left ventricles; by the end of week 5, the major heart chambers are partitioned, while the AV valves form during weeks 5–8 and the semilunar valves form during weeks 5–9.