Development of Heart Flashcards
Dextrocardia
The heart is directed to the right side of the body instead of the left side, people who have this disease are at an increased risk of having other congenital heart defects
Endocardial Cushions, why are they important
Formation of proper endocardial cushions is a key event in the development of heart, defects in the development of endocardial cushions leads to ASD, VSD, PDA, transposition of the great vessel and other defects
What cells are responsible for forming the endocardial cushions
Neural crest cells, they contribute to the cells that form the endocardial cushions.
They also form head and neck structures, individuals with craniofacial defects have an increased risk of developing defect in endocardial cushions
What happens when the atrial septation fails
Atrial septal defects arise. Clinical features are:
- These are usually asymptomatic
- These are usually detected when a murmur is heard, since blood is being pushed into the right side of the heart there will a fixed splitting of S2 due to late closure of the pulmonic valve
- Echo is needed for diagnosis
- It can be treated without an open heart surgery
Patent foreman ovale
It is not considered an ASD since no tissue is missing, it is simply the failure of the two atrial septal to fuse
When does the heart development begin
Day 19
- Vasculogenesis at the caudal end (cardiac region) leads to formation of horsehoe-shaped endocardial tubues
- Medial: becomes dorsal aorta
- Later the endocardial tubes become venous structures
Day 20
Embryo starts to fold cephalo-caudally and laterally which forms aortic arch.
Right and left endocardial tubes start to come together
Day 21
Lateral endocardial tubes differentiate to form the venous structure on each side
- Posterial cardinal veins
- Anterior cardinal veins
- Vitelline veins from the yolk sac
Single heart tube has been formed by the lateral fusion of the right and left endocardial tubies in the cardiogenic region
Day 21 to 23
Following structures are present in the cardiogenic region, from cephalic to caudal
- Sinus Venosis
- Atrium
- Ventricle
- Bulbis Cordis
- Truncus arteriosis
When does heart starts to beat
On day 22
Day 22
Spanchnopleuric mesoderm around the primitive heart starts to differentiate into two new layers:
- Myocardium: heart muscles
- Cardiac jelly: extracellular matrix secreted in between the myocardium and primitive endothelium of the heart tube
Mesothelial cells derived from splnachnopleuric mesoderm migrate towards the myocardium and form serous epicardium or visceral epicardium
Primitive pericardial cavity continues to form gaining a parietal layer of methothelial cells
Now there are 4 layers:
- Endocardium
- Cardiac jelly
- Myocardium
- Epicardium
Day 23
- The heart tube surrounded by the cardiac jelly begins to elongate, loop and fold on itself as it moves towards establishing the adult form
- The bulbis cordis grows so that it is displaced inferiorily, ventrall and to the right
- Sinus Venosis and atrium grow so they are superior and posterior
- Second aortic arch appears
What would happen if the heart doesnt fold or loop in proper direction
If the heart doesnt fold or loop in the proper direction then either dextracardia or situs inversis would develop.
People with situs inverusus have less chnaces of having congenital anomalies as compared to the people who have dextracardia
Day 25
Blood starts to circulate
- Ventricle start to differentiate into left and right primitive ventricle as this region increases in size and thickness
- The heart also starts to form a right and left atria though differential growth
Day 28
Endocardial Cushions form Septum Intermedium
- Heart starts the process of producing a seperate systemic and pulmonary circulation
- Two seperate masses of tissues (superior/anterior and inferior/posterior endocardial cushions) from the walls of the heart start to grow toward each other at the junction of the atrium with the ventricles
- These projections of the walls of the heart form the atrioventricular canals (opening filled with blood) and the septum intermediam (mass of tissue between the atrioventricular canals)
ASD
- About 20% of down’s syndrome patients have these defects
- ASD is thought to be caused by the failure of the endocardial cushion to form properly
- It may lead to lack of seperation of the mitral and tricuspid valves
- May relate to the problems of neural crest cells - Clinical symptoms are failure to thrive, need to take a breath during feeding and tachypnea.
Cyanosis can also be present
Partitioning of the embryonic atrium, how does that happen
- Right horn of the sinus venosus grows larger and starts to be incorporated into the posterior wall for the primitive atrium
- Anything derived from the sinus venosus will be smooth-walled - As the sinus venosus grows into the atrium, opening for SVC, IVC and coronory sinus starts to become seperate
- Pulmonary veins start to grow into the left, posterior wall of the primitive atrium
- On day 28 the septum primum grows down from the superoposterior wall of the atrium to being the process of forming a LA and RA, the forman ovale that connect the RA and LA is now called the ostium primum
- By 6th week the septum primum meeds and fuses with the septum intermedium, obliterating the ostium primun and forming a complete RA and LA
Early structure of the heart
What do endocardial cushions seperate
They seperate the atria from the ventricles
Explain the formation of the foreman ovale and its unidirectional flow of blood
The septum primum first starts to form in a heart when the endocardial cushions have finished to form proper divisions between the atria and the ventricles. However when this septum is just about to seperate the 2 atria completely, controlled cell death causes a hole on the top of this septum primum.
Septum secondum then forms which is a second septum that forms on one side of the septum primum and it itself is a hard septum, it leaves a hole in the middle which forms the foreman ovale. Now the foreman ovale has a hole (through septum secundum) and a valve (septum primum)
What happens when the atrial septation fails
There will be an atrial septum defects, usually this presents as a murmur, more blood is moving through the right side of the heart than the left side of the heart, this results in a fixed split of the pulmonic valve
The three types of atrial septal defects
What is patent foreman ovale
A patent foreman ovale is when the septum primum and septum secondum fail to fuse with each other, this is supposed to happen after birth, usually it is not a problem since the left atrial pressure is higher than the right atrial pressure but it can pose problems later in life nonetheless
It is not an atrial septal defect
What does it mean if the VSD is membraneous
It is from the top, this is the most common
Ventricular Septal Defects
- Isolated VSDs are the most common
- About 80% of these defects occur in the membraneous portion of the interventricular septum, which is perimembraneous
- More than half of VSDs close spontaneously until age 5
- They have systolic murmurs, which can be detected shortly after birth
Septation of the truncus arteriosis
The objective here is to divide the single vessel truncus arteriosis into aorta and pulmonary vessels and this is done with the help of conotruncal septum that divides the vessel that grows down and twist. When they grow down they either meet the spetan intermedium or it meets them, there is a dispute in the literature
What happens when it fails to form the interventricular septum
VSD
What happens when the conotruncal ridges dont grow properly
- Transposition of the great arteries
- Pulmonary stenosis
- Persistant truncus arteriosis
- Tetralogy of Fallot
What cells are responsible for the proper growth of conotruncal ridges
Neural crest cells
Transposition of the great vessels
Persistent truncus arteriosis
Tetralogy of Fallot
Pulmonary Stenosis
The more severe the splitting the greater the splitting of S2
Aortic Valve Stenosis
When do the valves begin to function
8 weeks
How do the chordae tendenae form for the valves
Their is controlled cell death that occur behind the chordae tendenae that allows them to start being functional
Coarctation of the aorta
Arches of the aorta
Theoretically there are 6 arches of the aorta but the 5th one never forms in humans. We only need to know the following:
Arch III: It forms the common and part of internal carotid artery in neck
Arch IV: Right subclavian artery on the right and arch of the arota on the left
Arch VI(6): Pulmonary arteries
What are the arteries that branch out of the aorta
Starting from left
Brachialcephalic artery
Left common carotid artery
Left subclavian artery
Define the circulatory system in the embryo
There are 3 circulatory systems
- Associated with the yolk sac is the vitelline veins
- Umbilical veins are associated with the placenta
- Cardinal veins serve the embryo
What forms the IVC and SVC
Right vitellin vein forms the inferior vena cava and the right anterior cardinal vein forms the SVC
IVC is formed by VItelline
What is the short cut called that bypasses the liver
Ductus venosus
What are the 2 important shunts that are normally present at bith
- Foreman ovale
- Ductus arteriosus
What is the function of the Eustachian valve
It causes the blood to bypass the right atrium and go straight into the foreman ovale and then to the left atrium
Explain the circulation system just before and after birth
Before birth:
- Lungs have very high resistance, minimal blood is made to pass through lungs
- Blood comes from the umbilical cord, passes through the liver via ductus venosus, goes into the right atrium where it is shoved by the eustachian tube into the left atrium via the foreman ovale.
- Aorta supplies some blood to the lungs via ductus arteriosis
After birth:
- New born starts to take breath through their lungs which causes the bradykinens to be released from the fetal lungs
- Rise in O2 causes the smooth muscles in the ductus arteriosis to constrict
Patent ductus arteriosis
What do you give to inhibit the closure of ductus arteriosis or accelerate the closure of ductus arteriosis
What kind of murmur is there
Where does cyanosis occur
To keep: Prostraglandin
To accelerate the closure: Indomethican
Machine like murmur
In the toes, not in the fingers
