Heart development and its common birth defects

Heart development, also known as cardiogenesis, refers to the prenatal development of the heart. This process begins with the formation of two endocardial tubes which merge to form the primitive heart tube. The heart is the first functional organ in vertebrate embryos.

Heart Development stages

Heart development is a complex process that begins early in embryogenesis and involves multiple stages and structures.

Formation of the Primitive Heart Tube

1. Cardiogenic Area:
   • Around 18 to 19 days after fertilization, the heart begins to form in the cardiogenic area near the head of the embryo.
   • Cardiogenic cords develop and form endocardial tubes.
2. Fusion of Endocardial Tubes:
   • The endocardial tubes fuse to form a single primitive heart tube.
   • This tube quickly differentiates into five distinct regions: truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and sinus venosus.

Heart Folding and Looping

1. Cardiac Looping:
   • Around day 23, the heart tube elongates and begins to fold, forming an S-shape.
   • This looping process establishes the foundation for the four-chambered heart.
2. Formation of Chambers:
   • The truncus arteriosus divides into the ascending aorta and pulmonary trunk.
   • The bulbus cordis develops into the right ventricle.
   • The primitive ventricle forms the left ventricle.
   • The primitive atrium becomes the anterior portions of both the right and left atria.
   • The sinus venosus develops into the posterior portion of the right atrium, the SA node, and the coronary sinus.

Septation and Valve Formation

1. Septation:
   • Septa form within the atria and ventricles to separate the left and right sides of the heart.
   • The atrial septum and ventricular septum develop to create distinct chambers.
2. Valve Formation:
   • The atrioventricular valves (tricuspid and mitral) and the semilunar valves (aortic and pulmonary) form to regulate blood flow through the heart.

Circulatory Shunts

1. Foramen Ovale:
   • A septal opening between the atria that allows blood to bypass the lungs in fetal circulation.
   • Typically closes after birth.
2. Ductus Arteriosus:
   • A vessel connecting the pulmonary artery to the descending aorta, allowing blood to bypass the lungs.
   • Closes shortly after birth.

Common Birth Defects

Congenital heart defects (CHDs) are structural problems arising from abnormal formation of the heart or major blood vessels. They are the most common type of birth defect.

Types of Congenital Heart Defects

1. Atrial Septal Defect (ASD):
   • A hole in the wall that separates the top two chambers of the heart.
   • Allows oxygen-rich blood to leak into the oxygen-poor blood chambers.
2. Ventricular Septal Defect (VSD):
   • A hole in the part of the septum that separates the heart's lower chambers.
   • Blood gets pumped back to the lungs instead of to the body.
3. Tetralogy of Fallot:
   • A combination of four heart defects that affect the structure of the heart.
   • Causes oxygen-poor blood to flow out of the heart and to the rest of the body.
4. Coarctation of the Aorta (CoA):
   • A narrowing of the major artery (the aorta) that carries blood to the body.
   • Affects blood flow where the arteries branch out to carry blood along separate vessels.
5. Pulmonary Valve Stenosis:
   • A defect in the pulmonary valve that causes it to become narrow or stiff.
   • Affects blood flow from the right ventricle to the lungs.

Diagnosis and Treatment

• Diagnosis: CHDs are often diagnosed through prenatal ultrasound or after birth using echocardiograms.
• Treatment: Many CHDs can be treated with surgery, heart catheterization, or medication.

References

19.5 Development of the Heart – Anatomy & Physiology https://open.oregonstate.education/aandp/chapter/19-5-development-of-the-heart/

Cardiovascular System - Heart Development - Embryology https://embryology.med.unsw.edu.au/embryology/index.php/Cardiovascular_System_-_Heart_Development

Embryonic Heart: Detailed Structure and Early Formation https://biologyinsights.com/embryonic-heart-detailed-structure-and-early-formation/

Development of the Cardiovascular System - TeachMeAnatomy https://teachmeanatomy.info/the-basics/embryology/cardiovascular-system/