In what direction does the caudal portion of the heart tube grow?
Dorsally, cranially and to the left
How do certain zones of the heart tube differ from others?
They grow at different rates
Give an example of where a zone of the heart tube grows at a different rate to the other?
Theres lots of growth of the ventricles, which causes the specific way the heart tube folds
What drives looping?
The limitation of space caused by tethering
What happens once looping is completed?
It pushes the outflow anterior to the inflow, producing the transverse pericardial sinus, and so the arteries end up in front of the veins
What does looping essentially do?
Puts everything in the right place to ensure that positioning can go ahead
Where does looping put the primordiums?
Puts the primordium of the right ventricle closest to the outflow tract, and the primordium of the left ventricle closes to the inflow tract
Where does looping put the atrium?
Dorsal to the bulbus cordis
What is the positioning of the individual domains/areas on the primitive heart tube critical to?
Establishing normal partitioning
What happens after looping?
The atrium communicates with teh ventricles via the atrioventricular canal
What does the atrioventricular canal result from?
The pinching of the primitive heart tube at the junction between the primitive atrium and the primitive ventricle
Are the chambers at the point after looping?
No, it is all continuous
What is initially true of the left and right sinus horns?
They are of equal size
What is true of the venous system in the embryo?
It is very symmetrical, with a highly symmetrical arrangement of venous drainage of placenta, yolk sac and body
What quickly happens to the venous system?
The symmetrical arrangement is lost, and venous return shifts to the right hand side, and so with right sinus horn becomes dominant, with the left sinus horn receding
What happens to the right sinus horn?
It is absorbed by the enlarging right atrium
What does the primitive atrium become?
Essentially, the right atrium
What is the right atrium also developed from?
The sinus venosus, as the right horn gets engulfed
What does the right atrium receive?
Venous drainage from the body (venae cavae) and the heart (coronary sinus)
What is the coronary sinus?
The remnant of the left sinus horn
What does the left atrium develop from?
A small portion of the primitive atrium. It also absorbs the proximal parts of the pulmonary veins.
What does the left atrium receive?
Oxygenated blood from the lungs
What does the embryo not commit a lot of energy to?
Structures that it doesn’t need until the end of development- the limb’s and lungs
When do limbs and lungs develop?
Towards the end of foetal life
What happens from the tiny zone of the primitive atrium that ultimately gives the left atrium?
A new vessel sprouts, the primitive pulmonary veins
What happens to the left atrium as development of the heart and lungs continue?
It engulfs the proximal parts of the primordial pulmonary veins, and then proceeds further out, until it ultimately engulfs all the way up, leaving the entrance of the four pulmonary veins
Why is there an oblique sinus within the pericardial sac?
Due to development/remodelling of the venous inflow to the developing heart tube
How is the oblique sinus formed?
As the left atrium expands, absorbing the pulmonary veins
What needs to be established in the foetus?
A foetal circulation that is dependant on oxygen rich blood coming from a place that doesn’t exist after birth- the placenta
How is foetal circulation from the placenta achieved?
Through the umbilical circulation