CVS - Development Of Heart Flashcards
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 Ventricle Atrium 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?
Right
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?
Liver
Right ventricle
Lungs
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
Endoderm
Mesdoerm
Ectoderm
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
Or
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?
ASD
VSD
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
