OSSF Cardiac Development

What are the 4 major learning objectives for cardiovascular development?

Describe development of the heart from a single tube into a four-chambered heart; describe development of the major veins and arteries; compare fetal vs adult circulation; list congenital malformations of the cardiovascular system.

What are the 5 regions of the primitive tubular heart?

Truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and sinus venosus.

What does the truncus arteriosus form?

The outflow tract of the heart, including the pulmonary trunk and aorta.

What does the bulbus cordis contribute to?

The right ventricle and part of the outflow tract.

What part of the bulbus cordis forms the right ventricle?

The dilated portion of the bulbus cordis.

What does the conus cordis form?

Part of the cardiac outflow tract.

What does the primitive ventricle form?

The definitive/adult left ventricle.

What does the primitive atrium form?

The adult right and left atria and their auricles/atrial appendages.

What does the right horn of the sinus venosus form?

The smooth-walled portion of the right atrium, called the sinus venarum.

What does the left horn of the sinus venosus form?

The coronary sinus.

What is the first asymmetrical organ to develop in the embryo?

The heart.

Before body folding, where is the primitive heart?

Cranial to the neural tube and notochord.

What happens to the heart during head folding?

The heart tube and pericardial cavity move ventral to the foregut.

What happens to the septum transversum during folding?

It becomes caudal to the heart.

Why is body folding important in heart development?

It changes the position of the heart and moves it caudally toward its eventual location.

What happens as the tubular heart elongates?

It develops alternating dilatations and constrictions and begins to loop.

What shape does the primitive heart tube form?

An S-shaped loop.

What is the purpose of cardiac looping?

It shortens the heart and brings the caudal end into the pericardial cavity while establishing the basic arrangement of the heart.

What happens to the inflow tract during looping?

The sinus venosus and primitive atria move from a caudal position toward a cranial position.

What are the major steps of early heart development?

Two tubes fuse, regions form, the tube expands and constricts, the heart loops, and the chambers and outflow tract are partitioned.

What are the endocardial cushions?

Developing structures that contribute to atrioventricular partitioning.

What do the endocardial cushions form?

The septum intermedium, which divides the AV canal into right and left AV canals.

What divides the atrioventricular canal into right and left canals?

The septum intermedium.

What signaling molecules stimulate endocardial cushion development?

TGF-β1, TGF-β2, and BMPs.

What are atrioventricular canals?

Openings connecting the atria to the ventricles.

What is the first atrial septum to develop?

The septum primum.

Where does the septum primum grow?

Dorsally to ventrally toward the endocardial cushions.

What is the ostium primum?

The opening between the septum primum and the endocardial cushions.

What happens to the ostium primum?

It closes as the septum primum grows toward and fuses with the endocardial cushions.

Why does another opening form as the ostium primum closes?

To maintain blood flow between the atria during fetal development.

How does the foramen secundum form?

Apoptosis creates multiple openings in the septum primum that merge into the foramen secundum.

Where is the foramen secundum located?

Within the septum primum.

What is the function of the foramen secundum?

It allows oxygen-rich blood to pass between the atria during fetal development.

What is the septum secundum?

A thick, muscular, crescent-shaped partition that develops to the right of the septum primum.

How does the septum secundum differ from the septum primum?

The septum secundum is thicker and more muscular.

Does the septum secundum form a complete septum?

No, it does not completely close.

What opening is left by the incomplete septum secundum?

The foramen ovale.

What is the function of the foramen ovale?

It allows fetal blood to flow from the right atrium to the left atrium, bypassing the nonfunctional lungs.

What structure forms the valve of the foramen ovale?

The septum primum.

What are possible atrial septal defects?

Persistent foramen ovale, holes in the septum primum, and holes in the septum secundum.

What happens if the foramen ovale does not close?

A persistent/patent foramen ovale results.

What happens during ventricular partitioning?

The ventricles are separated by muscular and membranous portions of the interventricular septum.

What is the bulboventricular sulcus?

The external groove representing the transition between the ventricle and bulbus cordis.

What develops internally at the level of the bulboventricular sulcus?

A muscular ridge that contributes to the muscular interventricular septum.

What closes the interventricular foramen?

The membranous interventricular septum.

Which direction does the muscular interventricular septum grow?

Dorsally.

Which direction does the membranous interventricular septum grow?

Ventrally.

What happens if the membranous interventricular septum does not fuse properly?

A ventricular septal defect can result.

What separates the bulbus cordis/conus cordis from the truncus arteriosus?

The aorticopulmonary/spiral septum.

What cells form the aorticopulmonary septum?

Neural crest cells.

How does the aorticopulmonary septum form?

Neural crest cells form ridges that spiral and fuse to separate the outflow tract.

What does the aorticopulmonary septum separate?

The developing aorta and pulmonary trunk.

What are the major congenital cardiovascular defects listed in this lecture?

Persistent foramen ovale, holes in the septum primum, holes in the septum secundum, failure of membranous interventricular septum fusion, and Tetralogy of Fallot.

What is the overall sequence of heart development?

Two tubes fuse → regions form → expansion/constriction → S-shaped looping → atrial partitioning → ventricular partitioning → outflow tract partitioning → four-chambered heart.

What is vasculogenesis?

Formation of new blood vessels from primordial endothelial cells.

Where does vasculogenesis begin?

In the yolk sac within blood islands formed from extraembryonic mesoderm.

Where does most vasculogenesis occur?

In the embryo proper/intraembryonic region.

What are blood islands?

Clusters of cells where primordial endothelial cells and blood-forming cells develop.

What are hemangioblasts?

Mesoderm-derived precursor cells that give rise to endothelial and blood-forming cells.

What is angiogenesis?

Sprouting of new blood vessels from pre-existing vessels.

Where does angiogenesis occur?

Around developing organs.

What is the difference between vasculogenesis and angiogenesis?

Vasculogenesis forms vessels from primordial endothelial cells; angiogenesis forms vessels by sprouting from existing vessels.

What signaling pathway promotes arterial development?

The Notch signaling pathway.

What does Notch signaling do to venous development?

It inhibits venous development and promotes arterial development.

What favors venous development?

Inhibition of the Notch pathway.

What are the two major extraembryonic venous systems?

Vitelline veins and umbilical veins.

What do the vitelline veins drain?

The yolk sac.

What do the umbilical veins connect?

The placenta with the fetus.

What are the major intraembryonic veins?

Cardinal, subcardinal, and supracardinal veins.

What are the two types of cardinal veins?

Cranial/anterior cardinal veins and caudal/posterior cardinal veins.

What do the subcardinal veins drain?

The mesonephric kidneys.

Where do the subcardinal veins develop from?

Outgrowths of the caudal cardinal veins.

What do the supracardinal veins drain?

The dorsal body wall.

What are the supracardinal veins important for forming?

The azygos veins.

What does the right vitelline vein contribute to?

The hepatic segment of the caudal vena cava, right hepatic vein, hepatic portal system, and ductus venosus.

What happens to vitelline veins within the liver?

They break up into small veins and capillaries.

What does the vitelline venous system contribute to?

The hepatic portal system and portions of the caudal vena cava.

What does the left vitelline vein contribute to?

The left hepatic vein and hepatic portal system.

What is the ductus venosus?

A fetal shunt that allows most oxygenated blood from the umbilical vein to bypass the liver and enter the caudal vena cava.

What happens to the right umbilical vein?

It mostly disappears.

What happens to the left umbilical vein?

It persists until birth and carries oxygenated blood from the placenta to the fetus.

Which umbilical vein is the major supplier of oxygenated blood to the fetus?

The left umbilical vein.

What does the left umbilical vein become after birth?

The round ligament of the liver.

What happens to the right umbilical vein in the liver?

A small portion contributes to vessels/capillaries within the liver.

What do the cranial cardinal veins form?

The internal and external jugular veins.

What does the left cranial cardinal vein contribute to?

The left brachiocephalic vein.

What do the right and left cranial cardinal veins and common cardinal veins form?

The cranial vena cava.

What do the caudal cardinal veins contribute to?

The common iliac, external and internal iliac veins, subclavian veins, and portions of the azygos veins.

What do the subcardinal veins contribute to?

The gonadal veins and part of the renal veins.

What do the right subcardinal and right vitelline veins contribute to?

The caudal vena cava.

What does the left supracardinal vein form?

The left azygos vein.

What does the right supracardinal vein form?

The right azygos vein and part of the caudal vena cava.

What do the right and left supracardinal veins contribute to?

Part of the renal veins.

What are the dorsal aortae?

Paired embryonic arteries that initially extend along the length of the embryo and later fuse to form a single dorsal aorta.