What influences the course of the recurrent laryngeal nerves?
The caudal shift of the developing heart The expansion of the developing neck region The need for a foetal shunt between the pulmonary trunk and aorta
What links the primitive atrium and ventricle?
Atrioventricular canal
What is created to divide the two primitive atria?
An interatrial septum
What is created to divide the two primitive ventricles?
The interventricular septum
What is the result of the septation of the outflow tract?
Blood is diverted from two separate ventricles into separate circulations through the pulmonary trunk and the aorta
What does septation, and the creation of the interventricular and interatrial septums create?
4 chambers, and selective outflow
Where do the beginnings of septation occur?
The atrioventricular canal
What is the purpose of the atrioventricular canal?
After looping, the atrium communicates with the ventricle via this canal
What are endocardial cushions?
Tissue growing in the walls of endocardium
Where do endocardial cushions start developing?
In the atrioventricular region
What do the endocardial cushions do?
Protrude out into the canal, pushing into the initially patent channel. They grow towards each other and fuse in the muddle
What does the fusion of endocardial cushions create?
A platform dividing the developing heart into right and left channels, and so the beginning of a structure towards which walls can grow
Why is atrial septation complex?
Because need to separate and create two discreet atria, but also allow for a foetal shunt
What does division of the common atrium involve?
Formation of two septa, with three holes to allow the opportunity for blood to shunt in foetal life
What is the septum primum?
A wedge of tissue that grows down towards the fused endocardial cushions from the roof of the atrium
What is the ostium primum?
The hole present before the septum primum fuses with the endocardial cushions
What happens before the ostium primum closes?
A second hole, the ostium secondum, appears in the septum primum
What is the septum secundum?
A second, cresent shaped septum that grows
What is present in the septum secundum?
A small hole, the foramen ovale
What is true of the foramen ovale and ostium secundum?
They are staggered
Why are the foramen ovale and ostium secundum staggered?
So there is a right to left shunt, as the blood entering the right atrium via the vena cava causes a high pressure, pushing the septums apart so blood can flow
What do both the left and right atria have?
The auricles
What are the auricles?
Components derived from the primitive atrium
What does the right atrium absorb?
The sinus venosus
What does the left atrium absorb?
The pulmonary vein it sprouted, and its 4 branches
What is the fossa ovalis?
The adult remnant of the shunt used in utero to bypass the lungs
What are the components of the ventricular septum?
Muscular and membranous
What does the muscular portion of the ventricular septum form?
Most of the septum
How does the muscular portion of the ventricular septum grow?
Upwards towards the fused endocardial cushions
What does the growth of the muscular portion towards the endocardial cushions leave?
A small gap called the primary interventricular foramen
