Embryology of The Heart Flashcards
What is the embryonic heart tube, and how does it form?
The embryonic heart tube is the primitive precursor of the heart, formed by the fusion of bilateral cardiogenic fields in the mesoderm. It initially presents as a linear tube composed of endocardial, myocardial, and epicardial layers. This tube undergoes looping and segmentation to establish the basic layout of the mature heart.
Describe the process of cardiac looping and its significance.
Cardiac looping is the bending and twisting of the linear heart tube into a more complex, S-shaped structure. This process, which occurs during the fourth week of development, is crucial as it establishes the spatial orientation and alignment of the future atria and ventricles.
What roles do the endocardial cushions play in cardiac septation?
Endocardial cushions are specialized swellings within the heart tube that contribute to the formation of the atrioventricular (AV) septum. They are essential in partitioning the heart into separate chambers by forming both the AV valves and the membranous portions of the interventricular septum.
Explain the development of the atrial septum and potential defects that can arise.
The atrial septum develops through a sequential process involving the formation of the septum primum and septum secundum. Failure in proper closure of this structure after birth can lead to an atrial septal defect (ASD).
How does the division of the truncus arteriosus contribute to the development of the great vessels?
The truncus arteriosus is divided into the ascending aorta and pulmonary trunk through the formation of a spiral (aorticopulmonary) septum. Improper septation can lead to persistent truncus arteriosus.
What is Tetralogy of Fallot, and how is it related to cardiac embryology?
Tetralogy of Fallot (TOF) is a congenital heart defect characterized by four anatomical abnormalities: ventricular septal defect (VSD), pulmonary stenosis, right ventricular hypertrophy, and an overriding aorta. TOF is often linked to malalignment of the infundibular septum during embryogenesis.
Define the development and clinical importance of the cardiac conduction system.
The cardiac conduction system develops from specialized myocardial cells and includes the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, and Purkinje fibers. Abnormal development can result in arrhythmias or conduction blocks.
What is ventricular septation, and what congenital anomalies can arise from its malformation?
Ventricular septation is the process by which the single primitive ventricle divides into right and left ventricles. Incomplete or abnormal septation can result in a ventricular septal defect (VSD).
How do neural crest cells contribute to cardiac development?
Neural crest cells migrate from the neural tube and play a crucial role in the formation of the outflow tract, including the aorticopulmonary septum. Disruptions can lead to conotruncal anomalies.
What embryological events are implicated in the development of coarctation of the aorta?
Coarctation of the aorta arises from aberrations in the remodeling of the aortic arch and the ductus arteriosus during fetal development.
Discuss the embryological basis and clinical implications of patent ductus arteriosus (PDA).
The ductus arteriosus connects the pulmonary artery to the descending aorta. Failure of closure results in a patent ductus arteriosus (PDA), which can cause persistent left-to-right shunting and increased pulmonary blood flow.
How does the remodeling of the cardiac jelly contribute to heart development?
Cardiac jelly plays a critical role in the early formation of cardiac structures and supports the formation of endocardial cushions. Proper remodeling is essential for structural integrity and functional differentiation of the heart.
When does the development of the heart begin?
Third week
What are the two endothelial strands formed during heart development called?
Angioblastic cords
What do the angioblastic cords form as they canalize?
Two heart tubes
What happens to the two heart tubes by the end of the third week?
They fuse into a single heart tube
By the fourth week, the developing heart receives blood from how many pairs of veins?
Three pairs
What are the names of the three pairs of veins supplying blood to the developing heart?
- Vitelline veins
- Umbilical veins
- Common cardinal veins
What type of blood do the vitelline veins carry?
Poorly oxygenated blood
From where do the umbilical veins carry blood?
Chorion, the primordial placenta
What type of blood do the umbilical veins carry?
Oxygenated blood
What do the common cardinal veins carry?
Poorly oxygenated blood from the rest of the embryo
What structure develops in close association with the septum transversum?
Primordial liver
What do the hepatic cords form as they surround epithelial-lined spaces?
Primordial hepatic sinusoids
How do the primordial hepatic sinusoids connect to the vitelline veins?
They become connected
What happens to the left vitelline veins during development?
They regress
What do the right vitelline veins form?
Hepatic veins
What forms around the duodenum from the network of vitelline veins?
Portal vein
What happens to umbilical veins as liver development progresses?
They lose connection with heart and empty into liver
What happens to the right umbilical vein and cranial part of the left umbilical vein during the seventh week?
They degenerate
What remains of the left umbilical vein after degeneration?
Caudal part of the left umbilical vein
What does the caudal part of the left umbilical vein carry?
Oxygenated blood to the embryo from the placenta
What connects the umbilical vein to the inferior vena cava (IVC)?
Ductus venosus
What is the function of the ductus venosus?
It directs most of the blood directly to the heart from placenta without passing through liver
What primarily drains the embryo?
Cardinal veins
The anterior cardinal vein drains the cranial part, and the posterior cardinal vein drains the caudal part.
What do the anterior and posterior cardinal veins form when they join?
Common cardinal vein
This vein enters the sinus venosus.
What vessel connects the anterior cardinal veins by the eighth week?
Oblique vessel
This vessel allows shunting of blood from the left anterior cardinal vein to the right.
What does the oblique anastomotic vessel become after the degeneration of the caudal part of the left anterior cardinal vein?
Left brachiocephalic vein
It forms as a result of the degeneration.
What do the right anterior cardinal vein and right common cardinal vein eventually become?
Superior vena cava (SVC)
They contribute to the formation of the SVC.
What do the posterior cardinal veins contribute to?
Common iliac veins and azygos vein
They are replaced by the subcardinal and supracardinal veins.
What do the subcardinal veins eventually form?
Parts of the left renal vein, suprarenal vein, gonadal vein, and inferior vena cava (IVC)
They supplement and replace the posterior cardinal veins.
What do the supracardinal veins form above the kidneys?
Azygos and hemiazygos veins
They are joined by anastomoses.
What does the right supracardinal vein contribute to?
Inferior vena cava (IVC)
The left supracardinal vein degenerates.
During which weeks do the pharyngeal arches form?
Fourth and fifth weeks of development
They are supplied by the pharyngeal arch arteries.
What do the pharyngeal arch arteries connect?
Aortic sac to the two dorsal aortae
This connection is crucial for embryonic development.
What do the dorsal aortae eventually fuse to form?
Lower thoracic/abdominal aorta
The right dorsal aorta degenerates, while the left remains as the primordial aorta.
What do the dorsal aortae give off?
The intersegmental arteries
What do intersegmental arteries supply?
The somites and their derivatives
What do intersegmental arteries become in the neck region?
The vertebral arteries
What do intersegmental arteries become in the thorax?
The intercostal arteries
What do intersegmental arteries become in the abdomen?
The lumbar arteries and common iliac arteries
What do intersegmental arteries become in the sacral region?
The lateral sacral arteries
What arises from the very caudal end of the dorsal aorta?
The median sacral artery
What are the unpaired branches of the dorsal aorta that supply the umbilical vesicle, allantois, and chorion?
Vitelline arteries
What supplies the foregut?
The celiac artery
What supplies the midgut?
The superior mesenteric artery
What supplies the hindgut?
The inferior mesenteric artery
What do the two umbilical arteries carry?
Poorly oxygenated blood from the embryo to the placenta
What do the proximal parts of the umbilical arteries become?
The internal iliac and superior vesical arteries
What do the distal parts of the umbilical arteries regress to become?
The medial umbilical ligaments
Fill in the blank: The umbilical vesicle is supplied by the _______.
vitelline arteries
True or False: The vitelline arteries give rise to the celiac artery, superior mesenteric artery, and inferior mesenteric artery.
True
What is the primordial myocardium?
The middle, muscular layer of the heart formed from splanchnic mesoderm around the pericardial cavity.
It separates the heart from the cardiac jelly.
What separates the primordial myocardium from the endocardium?
Cardiac jelly.
Cardiac jelly is a gelatinous tissue.
What is the innermost layer of the heart called?
Endocardium.
From where does the epicardium originate?
Mesothelial cells from the outer surface of the sinus venosus.
What happens to the heart tube as the cranial part of the embryo folds?
The heart tube elongates and develops alternating constrictions and expansions.
List the components formed from the bulbus cordis.
- Truncus arteriosus
- Conus arteriosus
- Conus cordis
What is the function of the truncus arteriosus?
It is cranial to the aortic sac and gives off the pharyngeal arch arteries.
How does blood leave the heart?
Via the pharyngeal arch arteries.
Name the veins through which blood returns to the sinus venosus.
- Umbilical veins
- Vitelline veins
- Common cardinal veins
What structural change does the heart undergo due to the faster growth of the bulbus cordis and ventricles?
The heart bends and folds in on itself, forming the bulbo-ventricular loop.
Where do the atrium and sinus venosus move during heart development?
They move to be dorsal to the truncus arteriosus, bulbus cordis, and ventricle.
What are the lateral extensions developed by the sinus venosus?
- Left horn
- Right horn
What is the dorsal mesocardium?
A mesentery that initially attaches the heart to the dorsal wall of the pericardial cavity.
What occurs to the dorsal mesocardium as the heart grows?
The central part degenerates, allowing communication between the left and right sides of the pericardial cavity.
What is formed as a result of the degeneration of the dorsal mesocardium?
The transverse pericardial sinus.
What structures does the sinus venosus receive blood from?
Common cardinal veins, umbilical veins, vitelline veins
The common cardinal veins carry blood from the embryo, umbilical veins from the placenta, and vitelline veins from the umbilical vesicle.
What is the pathway of blood flow after entering the sinus venosus?
Sinus venosus → sinuatrial valves → primordial atrium → atrioventricular (AV) canal → primordial ventricle → bulbus cordis → truncus arteriosus → aortic sac → pharyngeal arch arteries → dorsal aortae
This pathway allows blood to travel back to the embryo, placenta, and umbilical vesicle.
What structures begin partitioning in the developing heart during the fourth week?
Atrioventricular canal, primordial atrium, primordial ventricle
This partitioning process is completed by the end of week eight.
What are endocardial cushions?
Specialized extracellular matrix tissue related to myocardial tissue
They play a crucial role in the partitioning of the heart.
What is the foramen primum?
An opening between the edge of the septum primum and endocardial cushions
It allows blood to be shunted from the right atrium to the left.
What happens to the foramen primum as the septum primum elongates?
It progressively shrinks and eventually closes
The septum primum fuses with the endocardial cushions, forming the primordial AV septum.
How is the foramen secundum formed?
Apoptosis of cells in the middle of the septum primum creates perforations
This new opening allows oxygenated blood to continue flowing from the right atrium to the left.
What is the septum secundum?
A muscular septum that grows adjacent to the septum primum
It grows downward from the ventro-cranial wall of the atrium during the fifth and sixth weeks.
What is the foramen ovale?
An opening formed by the overlapping of the septum secundum over the foramen secundum
It allows oxygenated blood to flow from the right atrium to the left atrium.
What prevents blood from flowing from the left atrium to the right atrium?
The thin septum primum gets pressed against the more firm septum secundum
This blocks blood flow through the foramen ovale.
What forms the valve of the foramen ovale?
Residual parts of the septum primum that remain attached to the endocardial cushions
This occurs as the cranial part of the septum primum slowly regresses.
What happens to the pressure in the left atrium after a baby is born?
The pressure in the left atrium increases significantly, becoming much higher than the pressure in the right atrium.
What effect does the increased pressure in the left atrium have on the septum primum?
The septum primum is pushed against the septum secundum.
What happens to the valves of the foramen primum when the left atrial pressure increases?
The valves of the foramen primum fuse with the septum secundum.
What is the function of the foramen ovale after birth?
The foramen ovale functionally closes.
What does the foramen ovale become after it closes?
The foramen ovale becomes the fossa ovalis.
What is formed between the atria after the closure of the foramen ovale?
The two septae form a complete barrier between the atria.
What is the sinuatrial orifice?
The opening of the sinus venosus into the single primordial atrium
Where is the sinuatrial orifice initially located?
In the posterior wall of the primordial atrium
What happens to the sinuatrial orifice at the end of the fourth week?
It shifts to the right due to the larger growth of the right sinual horn
What does the right sinual horn receive blood from?
The head and neck region via the SVC and from the placenta and the rest of the body via the IVC
How does the sinus venosus integrate into the heart?
It becomes the smooth part of the internal surface of the right atrium, known as the sinus venarum
What is the appearance of the rest of the internal surface of the right atrium?
It has a thicker, trabeculated appearance
What demarcates the transition from the smooth to the rough internal surface of the right atrium?
The crista terminalis on the inside and the sulcus terminalis on the outside
What does the caudal part of the right sinuatrial valve form?
The valves of the IVC and coronary sinus
What does the left sinual horn develop into?
The coronary sinus
What happens to the left sinuatrial valve?
It fuses with the septum secundum, becoming part of the interatrial septum
Fill in the blank: The sinus venosus is integrated into the wall of the right atrium as the _______.
sinus venarum
True or False: The right atrium’s trabeculated parts originate from the sinus venosus.
False
What is the primary origin of the majority of the inner wall of the left atrium?
Derived from the primordial pulmonary vein
How many pulmonary veins enter the left atrium?
Four pulmonary veins
What is the left auricle’s origin?
Primordial atrium
What characterizes the internal surface of the left auricle?
Trabeculated
What begins the division of the primordial ventricle into two ventricles?
Growth of the median ridge
What is the interventricular (IV) septum?
A muscular septum with a superior free edge arising from the floor of the primordial ventricle
What is the IV foramen?
An opening between the upper free edge of the IV septum and the endocardial cushions
When does the IV foramen close?
At the end of the seventh week
What occurs when the left and right bulbar ridges fuse with the endocardial cushion?
Formation of the membranous part of the IV septum
What are bulbar ridges and when do they form?
Proliferations of mesenchymal neural crest cells in the walls of the bulbus cordis formed in the fifth week
What happens once the IV foramen closes?
The aorta becomes the sole outflow tract of the left ventricle and the pulmonary trunk becomes the sole outflow tract of the right ventricle
What results from the continued development of the ventricles?
Cavitation and formation of muscular bundles
What are trabeculae carneae?
Irregular columns of muscle on the inner surface of the ventricles
What do the papillary muscles and chordae tendinae connect?
Papillary muscles to the AV valves
What forms from mesenchymal neural crest cells in the truncus arteriosus?
Ridges similar to bulbar ridges
The migration of these cells is induced by bone morphogenic protein (BMP) and other signaling pathways.
How do the bulbar and truncal ridges spiral?
180-degrees
What does the fusion of the bulbar and truncal ridges form?
Spiral aorticopulmonary septum
What structures does the spiral aorticopulmonary septum divide?
Bulbus cordis and truncus arteriosus into the aorta and pulmonary trunk
What does the bulbus cordis become integrated into during heart development?
Ventricular walls as the smooth parts of the ventricles
What does the bulbus cordis become in the right ventricle?
Conus arteriosus
What does the bulbus cordis become in the left ventricle?
Aortic vestibule
How many swellings of subendocardial tissue develop into the aortic and pulmonic semilunar valves?
Three
What develops from proliferations of tissue surrounding the AV canals?
Tricuspid and mitral AV valves
How many cusps does the tricuspid valve develop?
Three
How many cusps does the mitral (bicuspid) valve develop?
Two
What initially functions as the developing heart’s pacemaker?
Primordial atrium
Which structure takes over the pacemaker role from the primordial atrium?
Sinus venosus
In which week does the sinuatrial (SA) node develop?
Fifth week
Where does the SA node develop?
In the right atrium near the opening of the SVC
What can be found near the opening of the coronary sinus after the sinus venosus is integrated?
Cells from its left wall
What structures are formed above the endocardial cushions?
AV node and bundle
What projects from the AV bundle into the ventricle?
Fibes
What do the fibers from the AV bundle divide into?
Left and right bundle branches
Where are the left and right bundle branches found?
Throughout the ventricular myocardium
What eventually provides nervous innervation to the SA node, AV node, and AV bundle?
Nervous system from outside the heart
What develops before the nervous innervation occurs?
Primordial conducting system
