Heart Development and Formation Quiz

Heart Development

• The cardiovascular system is the first major system to function in the embryo
• The primordial heart and the vascular system appear in the middle of the third week
• The rapidly growing embryo can no longer satisfy its nutritional and oxygen requirements from diffusion
• The heart is derived from mesoderm with contributions from the neural crest

Formation and Position of the Heart Tube

• The cardiogenic area is originally anterior to the future mouth and forebrain
• The forebrain grows over the heart to lie in the thorax position
• The lateral folding of the embryo brings paired cardiac tubes together as a single tube

Development of the Sinus Venosus

• The sinus venosus is a quadrangular space that precedes the atria
• The sinus venosus receives all blood for the embryo from the left and right sinus horns
• The left sinus horns contributes veins that degenerate and form the coronary sinus
• The right sinus horn enlarges from the shunting of blood
• The right sinus horn develops into the valves of the IVC and the valves of the coronary sinus

Formation of Cardiac Septa

• Endocardial cushions are growing masses of endocardium that project into the lumen to divide a canal
• These endocardial cushions form atrioventricular septa to divide the common atria
• The septum primum is a sickle-shaped crest that grows from the roof of the common atrium towards the endocardial cushions in the atrioventricular canal
• The ostium primum is an opening between the lower rim of the septum primum and the atrioventricular opening
• The ostium secundum are merging perforations in the septum primum that maintain blood flow between the atria
• The septum secundum is a crescent-shaped fold from the incorporation of the sinus horn in the right atrium
• The oval foramen is an opening left by the septum secundum, and this closes off after birth
• The oval foramen becomes the fossa ovalis after birth

Atrioventricular Valves

• Local proliferations of mesenchyme become fibrous and form the AV valves
• Muscular cords attaching the valves degenerate and are replaced by dense connective tissues
• The valves are attached to the papillary muscles by chordae tendineae

Septum Formation in the Outflow Tract

• Cardiac neural crest cells migrate to contribute to the outflow tract, disruption of migration can cause birth defects like tetralogy of Fallot, pulmonary stenosis, persistent truncus arteriosus, and transposition of great vessels
• The conotruncal ridges grow and divide the outflow tract into the aortic and pulmonary channels

Ventricular Septal Defects

• Occur in membranous or muscular portions
• Are associated with abnormal partitioning in the conotruncal region

Tetralogy of Fallot

• The unequal division of the conus due to the anterior displacement of the conotruncal septum
• This defect is associated with a patent ductus arteriosus and pulmonary stenosis

Transposition of the Great Vessels

• The conotruncal septum fails to take a spiral course and goes straight down
• The aorta originates from the right ventricle and the pulmonary artery from the left ventricle
• This defect is associated with a defect in the membranous IV septum and a patent ductus arteriosus

Septum Formation in the Ventricles

• The medial walls expand to form the muscular IV septum
• The membranous part of the IV septum closes the IV foramen
• Tubercles on the main truncus swellings form the semilunar valves, swelling is influenced by neural crest cells

Ebstein Anomaly

• The tricuspid valve is displaced toward the apex of the right ventricle
• This causes an expanded right atrium and a small right ventricle
• There are also abnormal valve leaflets