Lecture 7 Embryology Flashcards
Function of septation?
Separate the atria and ventricles.
Separate the aorta from the pulmonary trunk
Step 1 of septation?
The atrioventricular tract is divided in two by the growth of endocardial cushions which fuse together.
How are the atria separated?
Septum primum is already present. It grows down to fuse with the endocardial cushions and the ostium secundum forms to allow blood flow. Septum secundum then appears and the foramen ovale forms in it.
Why does the foramen ovale close?
In the uterus RA pressure is greater than LA pressure and so blood flows through the foramen ovale and keeps the septum primum and septum secundum separated. After breathing at birth the left sided pressure increases due to the pulmonary circulation and forces the septa to close and fuse together forming the fossa ovalis
Atrial septal defects?
Very common as septal formation is complicated.
Can be caused by failure of septa to form. Failure of one of the septa to form or the septum primum being reabsorbed or being too short etc
Ventricular septation?
Muscular and membranous components.
Muscular component grows upwards to endocardial cushions (opposite to atrial septum). Small gap left is filled by membranous ventricular septum.
Why do we get common defects in the endocardial cushions and membranous ventricular septum?
Endocardial cushions formed from cells outside the heart and membranous ventricular septum formed from endocardial cushions
What happens with a ventricular septal defect?
Blood from right and left ventricles can mix
What tissues result in the septation of the aorta and pulmonary trunk?
Endocardial cushions
What does the aorta and pulmonary trunk form from?
Ductus arteriosus through spiral septation
What are the two forms of congenital birth defects?
Structural abnormality
Complete absence of structure
What causes congenital heart defects?
Genetic
Exposure to agents like drugs and chemicals
Unexplained
Obstruction
Communication between pulmonary and systemic circulations
What is transposition of the great arteries?
Congenital heart defect where plumbing is back to front.
Causes cyanosis due to low O2 levels
What is tetralogy of fallot?
4 congenital heart defects together
Obstruction in right ventricle causes hypotrophy
What cells come from outside to make the endocardial cushions and what cells make the rest of the heart?
Neural crest cells make the endocardial cushions
Cardiogenic field cells make the rest of heart
