Systems development III: Cardiac embryology Flashcards
What percentage of all congenital defects are cardiac?
20%
Give a brief overview of the 7 main stages of cardiac development?
Folding brings heart tubes into ventral midline Heart tubes fuse (day 22) Heart tube begins to beat (32) Heart looping occurs Separation occurs Aortic and pulmonary trunks divide Valves develop
Where does the heart start to develop?
In the cardiogenic area inferior to the notochord
What do mesodermal and endothelial cells become?
Mesodermal- blood and vasculature
Endothelial- vessels at around week 3
Why does the heart tube fold?
To develop the 4 chambers of the heart
What do the ends of the heart tube divide to form at the anterior aspect?
The arterial trunks- then you have the ventricles followed by the atria. The venous channels or cardinal veins form at the inferior aspect
What does the heart do after the arterial trunks and venous channels are formed?
The heart tubes turn on the side to make a c shaped bending
What follows the c shaped bending?
S shaped bending to bring the atria and ventricles together
What does the gap between the atria and ventricles form?
AV groove
What is septation?
The process of the chambers being divided to form the atria and ventricles of the left and right sides of the heart
What is septation facilitated by?
Endocardial cushions which develop as outgrowths of mesodermal tissues in atrioventricular canal
What do the endocardial cushions eventually form?
The valves of the heart which separate the atria and ventricles
What little holes are there in the heart?
Septum primum grows downwards first and then the septum secondum. The foramen oval is formed from the gap between the AV body and the septum secondum
In the early embryo, what origin is all of the vasculature from?
Mesodermal
What are the first veins called?
Cardinal veins (with anterior/posterior and common branches
Where does aortic circulation come from?
Aortic arches
What happens to the first and second branches of the aortic arches in most people?
They regress
What does the third branch of aortic arches form?
Internal carotid arteries
What does the 4th aortic arch form in left and right artery?
Left- Aortic arch
Right- Right subclavian
What happens in terms of the 5th aortic arch in most people?
It may never develop
What does the 6th aortic arch form in the left and right artery?
Left- Ductus arteriosus and left pulmonary artery
Right- Right pulmonary artery
What has to happen prior to separation?
One tube needs to be partitioned into R or L outflow tracts
What do the partitions grow from?
Bulbar ridges- same process as endocardial cushions
What is the ultimate effect of the partitions forming?
There’s a 180 degree spiralling of vessels in the heart
How does blood from the mother come to the baby?
By the umbilical vein
How does the umbilical vein bypass the liver?
Via the ductus venous- it then enters the inferior vena cava
What happens when the blood from the mother reaches the right atrium?
It can either go into the R ventricle or bypass the pulmonary circulation through the foramen ovale
How does some of the blood that is being pumped through to pulmonary circulation from right ventricle get into systemic circulation?
Via the ductus arteriosus
In embryological circulation, where does the descending aorta carry blood?
Into the umbilical arteries which carries the blood into the placenta
What changes to circulation and heart occur at birth?
Clamping of umbilical cord causes closure of umbilical arteries- this then forms the median umbilical ligaments proximal portion, superior vesicle arteries
Taking a deep breath causes closure of umbilical vein and ductus venous
Closure of ductus arterioles
Closure of foramen ovale
What can go wrong at birth in terms of heart development?
The foramen oval remains patent- can be either idiopathic or iatrogenic
Why is the foramen ovale selectively kept open?
It is kept open with prostaglandins in babies who are at high risk of cyanotic heart disease to keep them deoxygenated
What is ventricular septal defect?
When there’s a hole between the ventricles which allows for blood to flow. The separation has malfunction- failure of the endocardial cushions which were responsible for ensuring the division process occurred properly
What is truncus arteriosus?
There is one common blood vessel leaving the heart, draining both R and L sides. In the majority, there’s also interventricular septal defect
What causes truncus arteriosus?
Defect in division of outflow tracts- bulbar ridges which form and separate the outflow tracts into 2 distinct vessels don’t form correctly
What is pulmonary stenosis?
Very serious condition where pulmonary vasculature doesn’t develop properly- pulmonary valves and blood vessels leaving the right side of the heart to the pulmonary circulation are very stenosed- usually a problem with outflow tracts
What is transposition?
Usually a looping defect where the incorrect folding of the tubes results in the right ventricle being connected to the aortic circulation and the left ventricle being connected to the pulmonary circulation
What is tetralogy of Fallot?
Four things have gone wrong-
Pulmonary stenosis, this then leads to muscles in wall of right ventricle thickening as have to pump harder and this high pressure system prevents endocardial cushions from functioning effectively which causes a ventricular septal defect to form. The aorta then has to override this septal defect due to the malformation in the rigght side of the heart- due to combination of developmental issues
