2.2 + 3.1 Development of the CVS Flashcards
When does lateral folding begin?
25 days after fertilisation
How does development of the CVS start?
Folding of the embryo to form the heart tube
What does cephalocaudal folding achieve?
Moves the heart tube into the thoratic region
What are the 6 areas of the primitive heart tube?
Aortic roots Truncus arteriosus Bulbus cordis Ventricle Atrium Sinus venosus
What occurs in cardiac looping?
The heart tube continues to elongate which results in bending.
In cardiac looping, how does the cephalic portion move?
Ventrally, caudally and to the right
In cardiac looping, how does the caudal portion move?
Dorsally, cranially and to the left
After looping, how does the atrium communicate with the ventrical?
Through the atrioventricular canal
Describe how the sinus venosus develops
The right and left sinus horns are initially the same size. Venous return shifts to the RHS and the left side recedes. The right sinus horn is absorbed by the enlarging right atrium.
How does the right atrium develop?
It develops from most of the primitive atrium and the sinus venosus.
How does the left atrium develop?
It develops from a small portion of the primitive atrium and absorbs proximal parts of the pulmonary veins.
How is the oblique sinus formed?
Formed as the left atrium expands absorbing the pulmonary veins
What is septation?
The formation of the interatrial and interventricular septum and the separation of the ventricular outflow tract to create 4 chambers.
What is the first step in septation?
The formation of the endocardial cushions which divides the heart into left and right channels.
Describe the first step in atrial septation. What is the hole called?
The septum primum grows down towards the endocardial cushions
The ostium primum is the hole present before the septum primum fuses with the cushions.
Describe the second step of atrial septation
Before the ostium primum closes, another hole, the ostium secundum appears in the septum primum.
Describe the third step of atrial septation
Finally, a crescent shaped septum, the septum secundum, grows from the roof of the heart downwards. The hole is called the foramen ovale.
How does the muscular portion form in ventricular septation?
It grows upwards towards the endocardial cushions leaving a small gap called the primary interventricular foramen.
How does the membranous portion of ventricular septation form?
It is formed by connective tissue derived by the endocardial cushions. It fills the gap of the primary interventricular foramen to complete the septum.
What happens in outflow tract septation?
Endocardial cushions appear in the truncus arteriosus. They twist as they grow towards each other to form a spiral septum.
Why fetal shunts necessary before birth?
The lungs are non-functional so blood is diverted around them and to the placenta instead to become oxygenated.
Why does the foramen ovale close at birth?
It closes because the pressure in the left atrium is greater than the pressure in the right atrium. The septum primum is pushed against the septum secundum.
