5. Development of the Cardiovascular System Flashcards
What is the first step of septation?
Formation of endocardial cushions in atrioventricular region. They divide the developing heart into right and left channels.
What happens in atrial septation?
Two septa form with three holes.
Septum primum grows down towards the fused endocardial cushions. Ostium primum is the hole that exists before this happens.
Before the ostium primum closes, the ostium secondum forms in the septum primum.
A second crescent shaped septum, septum secondum, grows and there is a hole in that - foramen ovale.
Where does the septum primum orginate from?
From the roof of the primitive atrium.
How are the Ostia formed in atrial septation?
By apoptosis.
What does the ostium secondum allow?
Blood flow between left and right atria.
What direction is blood flow between the atria in the primitive heart?
Right to left, down the pressure gradient.
What are the two components of ventricular septum?
Muscular (forms most of the septum and grows upwards toward fused endocardial cushions) and membranous components.
How does the primary interventricular foramen form?
The muscular portion of septum grows upwards towards endocardial cushion and leaves a small gap - the primary interventricular foramen.
How does the primary interventricular foramen close?
The membranous portion of the septum is derived from connective tissue of the endocardial cushions and it fills the gap.
What is the conotruncal septum?
The spiral septum of the outflow tract.
How does the conotruncal septum form?
Endocardial cushions are in the truncus arteriosus. They grow towards each other and twist around to form the septum.
Briefly summarise foetal circulation.
Lungs aren’t functional, so oxygenated blood comes from the mother via the placenta and umbilical vein. It returns to the placenta via umbilical arteries.
Where does blood enter the foetal heart?
The right atrium, hence why its pressure is higher than the left atrium.
What happens to the heart and circulation when the foetus is born?
Respiration begins so the left atrium pressure rises above that of the right atrium. This closes the foramen ovale and the circulation is now mature.
What happens to the following foetal shunts after birth?
Foramen ovale, ductus arteriosus, ductus venosus, umbilical vein.
Foramen ovale -> fossa ovalis
Ductus arteriosus -> ligamentum ateriosum
Ductus venosus -> ligamentum venosum
Umbilical vein -> ligamentum teres.
