Embryology of the Cardiovascular System

Comprehensive vocabulary flashcards covering the establishment of the heart fields, looping, cardiac chamber and septal morphogenesis, outflow tract partitioning, aortic arch derivatives, venous development, and fetal circulation.

Primary Heart Field (PHF)

A horseshoe-shaped cluster of progenitor cardiac cells located in the splanchnic layer of lateral plate mesoderm cranial to the neural folds; formed by cells that migrate through the primitive streak on approximately day $16$ of gestation to develop into the atria, left ventricle, and part of the right ventricle.

Secondary Heart Field (SHF)

A population of progenitor cells located in splanchnic mesoderm ventral to the pharynx; provides cells responsible for lengthening the arterial and venous poles, forming the remainder of the right ventricle, the outflow tract (conus cordis and truncus arteriosus), and part of the atria.

Cardiogenic Region

The horseshoe-shaped region of endothelial-lined tubes surrounded by myoblasts formed by the coalescence of blood islands in the splanchnic mesoderm cranial to the neural plate; overlies the intraembryonic cavity, which later develops into the pericardial cavity.

Cardiac Jelly

A thick, acellular layer of extracellular matrix rich in hyaluronic acid, secreted by the myocardium to separate it from the inner endothelial lining (endocardium) of the early heart tube.

Transverse Pericardial Sinus

A passage formed across the pericardial cavity when the central region of the dorsal mesocardium degenerates, leaving the heart suspended within the cavity only at its cranial and caudal poles.

Proepicardial Organ

A structure formed by mesenchymal cells located at the caudal border of the dorsal mesocardium; its cells proliferate and migrate over the surface of the myocardium to generate the epicardial layer (visceral pericardium) and coronary vasculature.

Cardiac Loop

The structural fold created between day $23$ and day $28$ when the elongating heart tube bends ventrally, caudally, and to the right in its cephalic portion, while the atrial (caudal) portion shifts dorsocranially and to the left.

Bulbus Cordis

A chamber of the early heart tube situated distal to the primitive ventricle; its proximal third forms the trabeculated part of the right ventricle, its midportion forms the conus cordis, and its distal part forms the truncus arteriosus.

Conus Cordis

The midportion of the bulbus cordis that undergoes septation to form the outflow tracts of both the left and right ventricles.

Truncus Arteriosus

The distal segment of the bulbus cordis that connects the conus cordis to the aortic sac; partitions via the aorticopulmonary septum into the proximal portions and roots of the aorta and pulmonary artery.

Bulboventricular Sulcus

The external groove between the primitive ventricle and the bulbus cordis, which marks the internal position of the primary interventricular foramen.

Dextrocardia

A congenital malformation in which the heart lies on the right side of the thorax instead of the left; caused by abnormal leftward bending/looping of the cardiac tube rather than rightward looping.

Situs Inversus

A congenital condition characterized by the complete mirror-image reversal of normal left-right visceral asymmetry throughout all thoracic and abdominal organs.

NKX2.5

The master transcription factor for heart development; homologous to the Drosophila gene tinman, containing a homeodomain whose expression in splanchnic mesoderm is induced by endodermal bone morphogenetic proteins (BMPs) and inhibition of WNT proteins by CRESCENT and CERBERUS.

Endocardial Cushions

Expansions of extracellular matrix covered by endothelium that appear in the atrioventricular canal and conotruncal regions; populated by migrating mesenchymal cells to form cardiac septa, atrioventricular canals, and valve leaflets.

Septum Primum

A crescent-shaped crest that grows down from the roof of the common atrium toward the endocardial cushions in the atrioventricular canal during atrial partitioning.

Ostium Primum

The temporary opening bounded between the free lower margin of the growing septum primum and the superior/inferior atrioventricular endocardial cushions.

Ostium Secundum

An aperture formed in the upper portion of the septum primum via coalescence of perforations generated by programmed cell death, maintaining continuous right-to-left shunting of blood before the ostium primum completely closes.

Septum Secundum

A thick, crescentic muscular fold that develops in the ceiling of the right atrium immediately adjacent to the septum primum; fails to form a complete partition, creating the oval foramen (foramen ovale).

Oval Foramen (Foramen Ovale)

An oblique interatrial aperture left by the free lower margin of the septum secundum; covered on its left atrial aspect by the remnant of the septum primum, which acts as a one-way valve allowing right-to-left blood shunting during fetal life.

Dorsal Mesenchymal Protrusion (DMP)

A proliferating mass of secondary heart field-derived mesenchyme from the caudal dorsal mesocardium that accompanies the septum primum into the atrium, guides the developing pulmonary vein into the posterior wall of the left atrium, and contributes to the atrioventricular cushions.

Sinus Venarum

The smooth-walled adult component of the right atrium derived from the incorporation of the expanding right horn of the sinus venosus.

Crista Terminalis

The internal muscular crest of the right atrium that demarcates the transition between the original trabeculated atrium (pectinate muscles) and the smooth-walled sinus venarum.

Total Anomalous Pulmonary Venous Return (TAPVR)

A vascular congenital defect in which pulmonary veins drain directly into the right atrium or systemic systemic veins (such as superior vena cava or brachiocephalic vein) instead of the left atrium, frequently caused by abnormal rightward deviation of the dorsal mesenchymal protrusion (DMP).

Aorticopulmonary Septum

A spiral partition formed by the growth, twisting, and midline fusion of the right superior and left inferior truncus swellings; divides the truncus arteriosus into the aortic channel and pulmonary channel.

Cardiac Neural Crest Cells

Ectoderm-derived migratory cells originating from the edges of hindbrain neural folds that migrate through pharyngeal arches $3$, $4$, and $6$ into the outflow tract, where they contribute to endocardial cushion formation and septation of the conus cordis and truncus arteriosus.

Muscular Interventricular Septum

The thick muscular wall formed by the apposition and merging of the medial walls of the expanding primitive ventricles, extending coronally toward the fused atrioventricular endocardial cushions.

Membranous Interventricular Septum

The thin superior portion of the interventricular septum that closes the interventricular foramen; formed by the fusion of tissue derived from the inferior atrioventricular cushion with the abutting right and left conus cushions.

Tetralogy of Fallot

The most frequent conotruncal malformation ($9.6/10{,}000$ births), produced by anterior displacement of the conotruncal septum; characterized by ($1$) pulmonary infundibular stenosis, ($2$) a large ventricular septal defect, ($3$) an overriding aorta, and ($4$) right ventricular hypertrophy.

Persistent Truncus Arteriosus

A condition occurring in $0.8/10{,}000$ births where conotruncal ridges fail to form and divide the outflow tract, leaving a single undivided arterial trunk overriding a ventricular septal defect that receives mixed blood from both ventricles.

Transposition of the Great Vessels

A congenital cardiovascular defect ($4.8/10{,}000$ births) in which the conotruncal septum fails to spiral and instead descends straight down, resulting in the aorta originating from the right ventricle and the pulmonary artery from the left ventricle.

Ebstein Anomaly

A congenital malformation of the heart where the tricuspid valve leaflets are displaced toward the apex of the right ventricle, producing an abnormally enlarged right atrium and a hypoplastic right ventricle.

Tricuspid Atresia

Complete obliteration or failure of development of the right atrioventricular orifice and tricuspid valve cusps, characterized by patency of the oval foramen, ventricular septal defect, underdevelopment of the right ventricle, and hypertrophy of the left ventricle.

Coarctation of the Aorta

A congenital constriction of the aortic lumen situated below the origin of the left subclavian artery ($3.2/10{,}000$ births); categorized as preductal (persistent ductus arteriosus) or postductal (associated with hypertrophied collateral intercostal and internal thoracic arteries).

Double Aortic Arch

A vascular anomaly caused by the persistence of the distal portion of the right dorsal aorta between the origin of the seventh intersegmental artery and its junction with the left dorsal aorta, creating a tight vascular ring around the trachea and esophagus.

Interrupted Aortic Arch (IAA)

A rare anomaly ($3/1{,}000{,}000$ live births) caused by abnormal regression patterns in the fourth aortic arches, producing a complete discontinuity between the aortic arch and descending aorta; commonly associated with DiGeorge syndrome ($22q11$ deletion).

Ductus Venosus

A large fetal venous channel connecting the left umbilical vein directly to the inferior vena cava, allowing the majority of oxygenated umbilical venous blood to bypass the hepatic sinusoidal capillary network.

Ligamentum Arteriosum

The post-closure fibrous connective tissue remnant of the embryonic ductus arteriosus, extending from the left pulmonary artery to the concavity of the aortic arch.

Ligamentum Teres Hepatis

The fibrous cord located in the free lower border of the falciform ligament after birth, representing the obliterated lumen of the intra-abdominal left umbilical vein.

Ligamentum Venosum

The fibrous connective tissue remnant of the fetal ductus venosus traversing the liver from the ligamentum teres hepatis to the inferior vena cava.