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Flashcards in CVS - Development Of Heart Deck (61):

What type of folding creates the heart tube?

Lateral folding - causes heart tubes to fuse together and create a substantial tube


What does cephalocaudal folding of the embyro achieve in relation to development of the heart?

Brings the tube into the thoracic region


When does the vascular system develop and why?

Middle of the third week when the embryo is no longer able to satisfy its nutritional requirements by diffusion alone


What cells form the atria, left ventricle and part of the right ventricle?

Progenitor heart cells from the primary heart field


Where is the heart tube suspended?

Pericardial cavity - by a membrane that subsequently degenerates


Name the 6 regions of the primitive heart tube

Aortic roots
Truncus arteriosus
Bulbus cordis
Sinus venosus (blood flow starts here)


What causes looping of the heart tube? What day does it begin/end?

Continued elongation of the heart tube to meet advancing needs of embryo. Grows into pericardial sac (fixed size) so needs to bend so it can all fit in
Essential for normal formation

Begins - Day 23
Ends - Day 28


What happens to the cephalic portion of the Heart tube during looping?

Bends ventrally, caudally and to the right


What happens to the caudal (artrial) portion of the heart tube during looping?

Dorsally, cranially and to the left (upwards to the left)


After looping, what sinus is created?

Transverse pericardial sinus


After looping, in what position are the arteries in relation to the veins?

Arteries in front of the veins


What does looping achieve? (3)

Primordium of right ventricle closest to outflow tract
Primordial of left ventricle closest to inflow tract
Atrium dorsal to bulbus cordis I.e. Inflow is dorsal to outflow


After looping, how does the atrium communicate with the ventricles?

Via the atrioventricular canal


During development of sinus venosus, where does the venous blood come from?

Left and right sinus horns


In which direction does venous return shift?

What happens to the remaining horn?

Left sinus horn recedes and rapidly looses importance.


Why is the right horn very important?

Forms the only communication between the original sinus venosus and the atrium


What structure is the right horn incorporated into?

Right atrium


Where does the right atrium develop from? (3)

Most from the primitive atrium
Sinus venosus
Receives venous drainage from the body (venae cava) and the heart (coronary sinus)


Where does the left atrium develop from? (3)

Small portion from the primitive atrium
Absorbs proximal parts of the pulmonary veins
Receives oxygenated blood from the lungs


When is the oblique pericardial sinus formed?

When the left atrium expands absorbing the pulmonary veins


What happens during fetal circulation?

Lungs are non functional
Receives oxygenated blood from the mother via placenta and umbilical vein
By passes the lungs
Returns to the placenta via umbilical arteries


What three areas does the fetal circulation by pass?

Right ventricle


Does any blood transfer into the lungs during fetal circulation?

Yes - a small amount transfers into the lungs for lung development


Why does fetal circulation by pass the lungs?

Lungs are non functional and it protects their development as the lungs are further behind in the developing program


What is the open vessel that is essential for fetal life?
Hint - in fetal circulation

Ductus arteriosus


Name the three germ layers



Where do the arteries and aorta arches arise from?

Aortic sac - the most distal part of the turn us arteriosus


How do the pharyngeal arches appear?

Cranially to caudally - so they are not all present simultaneously


How many pairs of arteries are there? And name them

5 pairs

1, 2, 3, 4 and 6.


How do the aortic arches appear?

How do they develop?

Early arterial system begins as a bilaterally symmetrical system of arched vessels.

Undergo extensive remodelling to create the major arteries


What does the 4th aortic arch form on the left? And the right?

Left - forms part of the arch of aorta between the left common carotid and the left subclavian arteries.

Right - most proximal segment of the right subclavian artery


What does the 6th aortic arch (pulmonary arch) form on the left? And the right?

Left - Left pulmonary artery and ductus arteriosus

Right - Right pulmonary artery


What does each aortic arch have?

A corresponding nerve


What nerve corresponds to the 6th aortic arch?

Laryngeal nerve


What two factors influence the course of the laryngeal nerve on the left and right?

Caudal shift of the developing heart and expansion of the developing neck region

The need for a fetal shunt between the pulmonary trunk and aorta


What do the endocardium, myocardium and epicardium line?

Endocardium - internal lining of the heart
Myocardium - muscular wall
Epicardium - covering the outside of the tube. Responsible for formation of the coronary arteries including their endothelial lining and smooth muscle


What are the three types of septation that must occur?

Intratrial septum

Interventricular septum

Seperation of the ventricular outflow tracts.- pulmonary trunk and aorta


How does a septum form?

What are the tissues masses that create septum called? Where do they develop?

Actively growing masses of tissue that approach each other until they fuse, dividing the lumen into two separate canals
A single tissue mass that continues to expand until it reaches the opposite side of the lumen

Endocardial cushions
Atrioventricular region


What do the endocardial cushions do?

Divide the developing heart into right and left channels


what does the atrioventricular canal provide?

A structure to which the walls of the heart can grow


What can abnormalities in the endocardial cushion formation cause?

Defects involving the great vessels (transposition of the great vessels, common truncus arteriosus and tetralogy of fallot


What is the septum primum?

When does it grow?

What direction does it grow?

Sickle shaped crest growing from the roof of the common atrium into the lumen

First septum to grow

Grows downwards towards the fused endocardial cushions


What is the ostium primum?

The opening between the lower rim of the septum primum and the endocardial cushions

Ostium = opening


What occurs before the ostium primum closes?

What does it do?

How is it formed?

A second hole - the ostium secundum appears in the septum primum

Ensures free blood flow from the right to the left primitive atrium

Cell death causes perforations in the upper portion of the septum primum which coalesce to form the ostium secundum.


What is the septum secundum?

How does it form?

What is the opening left by the septum secundum called?

The lumen of the right atrium expands as a result of incorporation of the sinus horn

A new crescent shaped fold appears = septum secundum

Foramen ovale


What develops in the right atrium?

And left atrium?

Right atrium absorbs the sinus venosus

Left atrium sprouts the pulmonary vein


What is the fossa ovalis?

Oval shaped depression

Adult remnant of the shunt used in utero to by pass the lungs


What is the oval foramen?

Which direction does blood flow between atria?

What happens to the oval foramen after birth?

Opening left by the septum secundum

Right to left flow through foramen oval due to higher pressure in the right atrium than left

When lung circulation begins and pressure in the left atrium increases the valve of the oval foramen is pressed against the septum secundum, obliterating the oval foramen and separating the left and right atria.


What are the two components of the ventricular septum?

What do they form?

Muscular - forms most of the septum and grows upwards towards the fused endocardial cushions

Membranous - 'fills the gap' between the interventricular septum and the endocardial cushions.


What is the primary interventricular foramen?

When the muscle portion has grown upwards towards the endocardial cushions leaving a small gap


How are valves connected to the walls of the ventricle?

Papillary muscles via the chordate tendineae.


How does septation of the outflow tract (conotruncal septum) happen?

Endocardial cushions appear in the truncus arteriosus.
As they grow towards each other, they twist around each other.
Complete fusion divides the truncus into an aortic and pulmonary channel


Why may you see facial and cardiac abnormalities in the same individual?

The neural crest cells also contribute to craniofacial development.

The neutral crest cells contribute to endocardial cushion formation in both the conus cordis and truncus arteriosus.


Why may outflow tract defects occur?

Give an example of a defect

Insults to the secondary heart field

Insults to the cardiac neural crest cells that disrupt formation of the conotruncal septum

Tetralogy of fallot, pulmonary stenoses, persistent truncus arteriosus and transposition of the great vessels


Describe blood flow in fetal circulation

Blood moves from inferior vena cava - where blood mixes with deoxygenated blood which returns from the lower limbs i
Enters right atrium
Guided towards the foramen oval by valve of inferior venacava and most blood passes directly into left atrium
Blood enters left ventricle and ascending aorta

Desaturated blood from superior vena cava flows from right ventricle into pulmonary vessels


What causes the changes in the vascualr system at birth?

Respiration and cessation of placental blood flow


Why does the amount of blood flowing through lung vessels increase rapidly?

What effect does this have on the pressure of the left atrium?

What closes? And why

Ductus arteriosus closes by muscular contraction of its wall

Increases pressure in left atrium

Oval foramen closes - due to decreased pressure in the right atrium as a result of interruption of placental blood flow.


What happens to the

Placental support
And ductus venousus
Ductus arteriosus
Oval foramen

After birth?

Placental support removed

Ductus venosus closes

Ductus arterious contracts and closes - immediately after birth, mediated by bradykinin (substance released from the lungs during initial inflation)

Oval foramen closes - due to increased pressure in left atrium, combined with decreased pressure on right side. The first breath presses the septum primum against the septum secundum


Name the four fetal shunts?

What is their fate

Foramen oval --> fossa ovalis
Ductus arterious --> ligament arteriosum
Ductus venousus --> ligament venosum
Umbilical vein --> ligament teres


What is the most common heart defect?

VSD - ventricle septum defect
Hole between atria or ventricles


Name four heart defects

What is the incidence of heart defects?

ASD - atria septal defect
VSD - ventricle septal defect
Transposition of the great vessels - conotruncal septum does not adopt spiral course. Defect effects outflow tract
Tetralogy of Fallot - unequal divisions of conus cordis

Very common 6-8/1000 births