Embryonic Heart Development Quiz

Development of the Cardiovascular System-I

• Vasculogenesis and angiogenesis are fundamental processes in blood vessel formation.
• Vasculogenesis is the differentiation of endothelial precursor cells (angioblasts) into endothelial cells, creating a primitive vascular network.
• Angiogenesis is the growth of new capillaries (lacking a fully developed tunica media) from existing blood vessels.
• The cardiac crescent forms within the splanchnic mesoderm.
• The intraembryonic coelom develops into the embryonic body cavity, divided into three cavities (pericardial, pericardioperitoneal, peritoneal) during the fourth week.
• Pericardiac mesoderm forms the heart-forming regions.
• The cranial-most portion of the cardiac crescent shifts ventrally and caudally, positioned ventral to the foregut endoderm.
• During the head fold, the pericardial coelom moves ventral to the heart tube and caudal to the oropharyngeal membrane.
• Endocardial tubes coalesce into a single tube, forming the primitive heart tube.
• The embryo folds cephalocaudally and transversely to bring the two heart tubes closer.
• The two endocardial heart tubes fuse in the cephalo-caudal direction.
• The heart tube is attached to the dorsal side of the pericardial cavity by the dorsal mesocardium.
• Cardiogenic cords differentiate into endocardial heart tubes.
• The primitive heart tube begins to elongate and bend into a C-shape, with the bend extending to the right side.
• This looping process establishes the proper spatial relationship for the four chambers of the heart.
• The heart's chambers progressively form (truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and sinus venosus).

Major Cardiovascular Structures

• The four presumptive chambers of the future heart are brought together through cardiac looping.
• The primary heart tube comprises an endocardial tube, cardiac jelly, and myocardial tube.
• The innermost endothelial tube becomes the endocardium.
• The outermost myocardial tube, a mass of splanchnic mesoderm, forms the myocardium.
• The layer of extracellular matrix around the myocardium is the cardiac jelly.
• Splanchnic mesoderm migrating from the coelomic wall near the liver forms the epicardium.
• The tubular heart elongates and develops alternative dilations and constrictions, forming the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and sinus venosus.

Development of the Heart Valves

• Semilunar valves develop from three swellings of subendocardial tissue around the orifices of the aorta and pulmonary trunk; these swellings become hollowed out and reshaped, forming three thin-walled cusps.
• Semilunar valve leaflets originate from endocardial-derived cushion tissue.
• Atrioventricular valves (tricuspid and mitral valves) develop similarly from localized proliferations of tissue around the atrioventricular canals.
• The bulbar ridges and truncal ridges, primarily derived from neural crest cells, grow, twist, and interact spirally, potentially influenced by blood flow from the ventricles.
• The aorticopulmonary septum develops from ridges, dividing the bulbus cordis and truncus arteriosus.
• The pulmonary trunk twists around the ascending aorta due to spiraling of the aorticopulmonary septum.

Formation of Atrial Septum

• The primordial atrium is divided into right and left atria through the formation and modification of two septa-the septum primum and septum secundum.
• The septum primum grows toward the fusing endocardial cushions, partially separating the atrium into right and left halves.
• The foramen primum—a large opening between the free edge and endocardial cushions—forms as the septum primum develops.
• The foramen primum closes when the septum primum fuses with the atrioventricular cushions.
• Perforations produced by apoptosis develop in the central part of the septum primum and coalesce to form the foramen secundum.
• The septum secundum develops from the muscular ventrocranial wall, adjacent to the right side of the septum primum.
• The foramen ovale is the opening between the upper and lower limbs of the septum secundum.
• During embryonic life, the foramen ovale shunts blood from the right atrium to the left.

Fetal Heart Circulation

• In the fetus, most blood bypasses the lungs through the foramen ovale, which is an opening between the atria (right to left), and the ductus arteriosus that connects the pulmonary artery and the aorta.
• Blood from the embryo enters the sinus venosus through the common cardinal veins (poorly oxygenated) and from the developing placenta via the umbilical veins (well-oxygenated).
• Blood leaves the truncus arteriosus, enters the aortic sac, and is distributed to pharyngeal arch arteries.
• The closure of the interventricular foramen and formation of the membranous interventricular septum result from the fusion of the right and left bulbar ridges and endocardial cushions.

Transitional Circulation

• Transitional circulation is when fetal circulation changes to the neonatal phenotype.
• It begins when the umbilical cord is clamped, and the lungs begin aeration.
• Elimination of placental circulation, expansion of lungs, increase in lung blood flow, closure of the foramen ovale, ductus arteriosus, and ductus venosus are key components of the transition.
• The period of time for this transition to complete varies, but it generally happens soon after birth.
• Factors like cold stimuli or the first few breaths after birth contribute to the transition.

Congenital Heart Defects

• Some congenital conditions include Atrioventricular septal defect, Hypoplastic left heart syndrome, Tetralogy of Fallot, Ventricular septal defect, Transposition of great arteries, Coarctation of the aorta, Double outlet right ventricle, Aortic stenosis, Tricuspid atresia, Single ventricle, Ebstein's anomaly, Common arterial trunk, Pulmonary atresia, and Pulmonary atresia with an intact ventricular septum, as well as others.

Specific Cardiovascular Anomalies

• Truncus arteriosus is a congenital defect where the fetus or newborn baby has just one large blood vessel emerging from the heart instead of two separate vessels.
• Atrial septal defect is a structural anomaly where the septum between the atria has an opening, allowing oxygenated blood from the left atrium to flow into the right atrium.
• Ventricular septal defect is a condition where the ventricular septum has an opening, obstructing oxygenated blood from the left ventricle from flowing into the right ventricle.
• Tetralogy of Fallot involves four cardiac anomalies: ventricular septal defect, overriding of the aorta, narrowing of the pulmonary outflow tract and thickening of the right ventricular wall.
• Atrioventricular canal (Endocardial cushion defect) is an anomaly where the division of the primordial ventricle to two ventricles isn't completely formed.