Cardiovascular embryology Flashcards
What germ layer are the 3 layers of the heart derived from?
Endocardium - endoderm
Myocardium - visceral mesoderm
Epicardium - visceral mesoderm
What are endocardial tubes formed from?
Angioblasts which cells derived from the endoderm
The endoderm signals to cells overlying the visceral mesoderm to form angioblasts
How is the primitive heart tube formed?
From the fusion of the 2 endocardial tubes during lateral folding of the embryo
What is cardiac jelly?
Thick layer of extracellular matrix secreted by the myocardium formed from the visceral mesoderm overlying the heart tube What
What is the cardiac jelly important for?
Partitioning the heart into 4 chambers
What brings the developing heart into the thorax?
Cranio caudal folding of the embryo
What layer of the heart is responsible for the formation of the coronary arteries?
The epicardium
Where does the cardiac jelly lie?
Inbetween the endocardium and myocardium
What 3 paired veins drain into the caudal region of the heart in the 4 week old embryo? What do they drain in via?
1) Common cardinal vein
2) Vitelline vein
3) Umbilical vein
Drain via the left and right horns of the sinus venosus
What does the cranial region of the heart connect to in the 4 week old embryo?
2 dorsal aortae
With differential growth of the heart tube which 5 dilatations become apparent?
1) Truncus arteriosus
2) Conus arteriosus
Above 2 are collectively called the bulbus cordis
3) Primitive ventricle
4) Primitive atrium
5) Sinus venosus
On what day does the heart start to fold into 4 chambers?
23
What are the 3 structures the heart forms in folding?
1) Straight heart tube
2) C shaped loop
3) S shaped loop
When does the sinus venosus degenerate and what does it from in the adult heart?
Degenerates by week 5
It remains as part of the wall of the R atrium and the left horn forms the oblique vein of the left atrium and the coronary sinus
What is the embryological origin of the coronary sinus and the oblique vein of the left atrium?
Left horn of the sinus venosus
What does the right horn of the sinus venosus form in the adult heart?
The smooth part of the wall of the right atrium called the sinus venarum
Clear border between the trabeculated part and the smooth part called the crista terminalis
What is the ventricular wall formed from?
The primitive atrium with small contributions from the conus arteriosus
What part of the ventricles does the conus arteriosus form?
The smoothed walled part leading up into the aorta called the aortic vertibule and the smooth part leading up to the pulmonary artery called the conus arteriosus
What are the ridges on the ventricular wall called?
Trabeculae carnae
What do the pulmonary veins arise from?
An outgrowth of the left atrial wall forms a single pulmonary vein which then bifurcates twice to split into 4 pulmonary veins which are then incorporated into the wall of the left atrium by intussusception
In what week are the 4 pulmonary veins incorporated into the wall of the left atrium by intussusception?
Week 5
What forms the atrioventricular septum?
Fusing of the dorsal and ventral endocardial cushions (from the endoderm) in the midline
When does the septum primum form?
At end of week 4
What is the foramen primum?
The diminishing connection between the left and right atrium as the septum primum extends
Why does the ostium/foramen primum become obliterated and when?
Because the septum primum fuses with the AV septum by week 6
How is the foramen secundum formed?
The upper part of the septum primum undergoes apoptosis
What is the septum secundum?
A second growth from the posterior atrial wall
What is the foramen ovale and how is it formed?
The septum secundum does not fuse completely with the AV septum and leaves a small hole called the foramen ovale
What does the foramen ovale and foramen secundum allow?
Septum secundum is flimsy, acts like a valve allows right to left shunt of blood to by pass the lungs as blood already oxygenated by the mother
What are the 2 origins of the interventricular septum?
1) A muscular part that projects from the floor of the primitive ventricle towards the endocardial cushions leaving an interventricular foramen in week 4
2) A membranous part that projects inferiorly from the endocardial cushions to close the interventricular septum in week 7
What are the conotruncal ridges?
2 swellings which separate the truncus arteriosus into 2 channels
What forms the conotruncal septum and what does it connect to?
The fusion of the conotruncal ridges
Fuses with the interventricular septum
In what formation do the conotruncal swellings fuse?
In a spiral shape so that the left ventricle connects with the aorta and the right ventricle with the pulmonary artery
From what germ layer are the conotruncal swellings and therefore the conotruncal spetum derived?
The neural crest cells
How does oxygenated blood reach the fetus?
Through the umbilical vein
What is the oxygen content of the blood entering the right atrium from the SVC in the fetus and where does it come from?
Poorly oxygenated
Blood returning from the lungs
What is the function of the ductus arteriosus?
Allow blood to pass from the pulmonary artery to the aorta thus bypassing the lungs
Why does the foramen ovale close in the newborn?
First breath causes pulmonary arteries to dilate and blood returning from the lungs causes the pressure in the left atria to rise, closing the foramen ovale
What causes the ductus arteriosus to constrict and what does it form in the adult?
Frist breath causes increase in oxygen tension which along with a decrease in circulating prostaglandins causes the ductus arteriosus to constrict
Forms the ligamentum arteriosus in the adult
For what 2 reasons could dextrocardia occur?
abnormal cardiac looping or abnormal gastrulation when laterality is determined
What other malformations of the heart is isolated dextrocardia associated with?
1) Abnormal septation of the heart
2) Abnormal connections with arteries and veins
What 3 problems can a patent ductus arteriosus lead to in an adult and why?
1) Pulmonary hypertension - Blood from aorta going to pulmonary artery ie. too much blood going to the lungs
2) Ventricular hypertrophy - as oxygenated blood is returning to the lungs the heart is having to work extra hard
3) Heart failure as heart is overworked
How is a patent ductus arteriosus treated?
With prostaglandin inhbitors
What is a probe patent foramen ovale?
Failure of septum primum and secundum to fuse after birth
What happens in ostium secundum defects?
Can be caused either by excessive apoptosis of the septum primum or inadequate development of the septum secundum so the foramen ovale and foramen secundum overlap
Which way is blood shunted in ostium secundum defects and what can this lead to?
From left to right
Enlarged right atrium and ventricle
How is ostium secundum treated?
Small defects may be asymptomatic but larger defects (>5mm) may require surgical repair
What is cor triloculare biventricular and why does it occur?
Common atrium
Failure of septum primum and septum secundum to develop
What happens to the structure to the heart in premature closure of the foramen ovale and what consequences does that have for the newborn?
Closing of the foramen ovale during pre natal life
Results in hypertrophy of the right side of the heart and under development of the left
Death usually occurs after birth
What is the most common congenital heart defect?
Ventricular septal defect
What shunt occurs in VSD and what consequences does this have?
Left to right
Results in right ventricular hypertrophy and can result in pulmonary hypertension
How are VSDs affecting the muscular part of the septum resolved?
Normally resolve themselves as the child grows
What causes septation defects of the conus arteriosus?
Abnormal migration of development of neural crest cells
What is patent truncus arteriosus, what is its symptoms and how is it corrected?
Absent conotruncal septum, not present to fuse with the interventricular spetum so also get a VSD
Symptoms = cyanosis, breathlessness, delayed growth and lethargy
Must be corrected surgically or will result in heart failure and death within 2 years
Why does transposition of the great vessels occur?
Conotruncal septum does not form in a spiral but goes down in a straight line instead
What else must exist to allow survival with transposition of the great vessels and if so how is it corrected?
Another defect such as VSD, patent foramen ovale or patent ductus arteriosus
Similar symptoms to patent truncus arteriosus
can be corrected surgically
What are the 4 defects in tetralogy of Fallot?
1) VSD
2) Overriding aorta
3) Pulmonary stenosis
4) Right ventricular hypertrophy
What is coarctation of the aorta and how can it be classified?
Narrowing of the aorta close to the ductus arteriosus
Can be classified as pre ductal or post ductal in relation to the ductus arteriosus
How does the body compensate for pre ductal coarctation of the aorta during development and after birth?
During development the ductus arteriosus compensates for the narrowing
After birth the ductus arteriosus remains patent, if not get rapid decline of the infant with hypoperfusion of the lower body
Why does differential cyanosis occur in coarctation of the aorta?
Upper body well perfused
Lower body poorly perfused
How can pre ductal coarctation of the aorta be treated?
With prostaglandins to keep the ductus arteriosus open
How does the body compensate for post ductal coarctation of the aorta?
During development a collateral circulation is established to compensate for the narrowing
Blood flows through the subclavian arteries to the internal thoracic arteries and via the intercostal arteries to the aorta
Internal thoracic arteries enlarge to carry greater blood flow
