The Development of the Heart Flashcards
Outline the 5 normal developmental processes.
- Formation of the 4 chambered heart tube
- Cardiac looping
- Division of the atrioventricular canal into left and right channels
- Formation of the atrial septa
- Formation of the conotruncal cushions and division of the outflow tract
What is situs inversus? What is situs inversus totalis?
Where organs form on the opposite side of where they should be.
Where all viscera form on the opposite side of where they should be.
What is dextrocardia and how does it arise?
It is when the heart alone forms on the right hand side and arises when the TF lefty leads to the lefty gene being expressed on the right hand side.
What is ventricular septal defect and how does it occur?
When the ventricle doesn’t have endocardial cushions to attach to as they don’t develop properly, it flops about in space which means the higher BP on the systemic side will mix with the pulmonary side – blood trying to pump to body will instead go to your lungs. This disease can occur anywhere during the hearts development.
What is atrial septal defect and how does it occur?
It’s a congenital heart defect in which blood flows between the atria of the heart because the interatrial septum is defective or absent.
What is Tetralogy of Fallot?
It is a congenital heart defect consisting of 4 defects that include: ventricular septal defect, pulmonary stenosis(narrowing of exit from right ventricle), right ventricular hypertrophy(enlargement), overriding aorta(blood from both ventricles can enter aorta).
Describe formation of the heart tube.
Blood islands combine to make a tube. The process takes starts at 18 days and ends at 22 where a truncus arteriosus and sinus venosus are formed. Looks like a ball with 2 vessels coming out the top and 4 out the bottom.
Describe the process of cardiac looping.
The heart grows and folds in on itself making the ball look like an ‘S’ shape. This process occurs from 22 to 35 days. At 24 days the heart’s future left atrium on corner of the ‘S’ folds back and up around the heart. At 35 days the heart has the right and left primitive atria folded back and upwards onto the right and left primitive ventricles.
At what day do the chambers begin to separate?
30
Outline the formation of the atrial septa?
Septum primum is a thin membrane of myocardium – it forms as the endocardial cushions (two areas of thickening that eventually develop into the wall that separates the four chambers) grow together – it forms the first layer of separation in the atria. Then the septum secondum forms, by this time the endocardial cushions have merged and you have left side and right side of the heart between atria and ventricles.
Explain how in a developing heart a foetus has a blood supply?
As septum primum closes over a second hole appears in it. Septum secondum develops incompletely and forms a foramen ovale – this is the bypass circuit for blood whilst a foetus (don’t need to pump blood to lungs as they are full of water and not developed). Blood is collected from veins through foramen ovale through foramen secondum to rest of body. When born the 2 sheets fuse together and the hole closes.
Describe the division of outlaw tract.
Separation of the ventricles results from the union of the conotruncal septum, endocardial cushions and ventricular septum. Ventricles start to grow from the bottom up, from the ventricular septum heading up to the endocardial cushions and conotruncal septum.
