CVS 5 - Development Of The Heart Flashcards
What is the estimated worldwide incidence of congenital heart defects?
Around 1% (most common birth defect)
Give some causes of congenital birth defects
- genetic
- exposure to chemicals/drugs/infectious agents
- can arise ‘de novo’
Why are some heart defects only apparent after the child is born?
Because the foetus has a different circulatory route to the newborn, so defects may not impact the foetal circulation.
What falls within the classification of a ‘heart defect’?
- structural defect or chambers or vasculature
- obstruction
- communication between pulmonary and systemic circulations
What does the foetal heart look like before folding?
One long tube (basically a modified blood vessel) with an inlet and outlet but no valves
Briefly describe the act of ‘looping’ of the primitive heart tube
- tube elongates and runs out of room in the pericardial sac
- twists and folds up in a regular and predictable way
What does the right atrium develop from?
Most of the primitive atrium and the sinus venosus
What does the right atrium receive?
Venous drainage from the body and the heart
What does the left atrium develop from?
A small portion of the primitive atrium and absorbs proximal parts of pulmonary veins
What does the left atrium receive?
Oxygenated blood from lungs
Why does a foetus require shunts in its heart?
The lungs do not work before birth, so these must be bypassed by circulation
Why must the liver be bypassed in foetal circulation?
It is very metabolically active and could consume all the oxygenated blood before it was able to reach the rest of the body
What are the three shunts in the foetal heart?
- ductus venosus
- foramen ovale
- ductus arteriosus
What is the name given to the early arterial system which begins as a bilaterally symmetrical system of arched vessels?
The aortic arches
What does the 4th aortic arch become?
Part of subclavian artery and arch of aorta
What does the sixth arch become?
The left and right pulmonary arteries, ad ductus arteriosus
How is the foramen ovale constructed?
- septum primum forms (this is a flap that partially blocks passage of blood)
- ostium secundum forms (this is a hole in the septum primum)
- septum secundum forms (a second flap with a hole in it)
How is the foremen oval closed after birth?
Pressure in the left atrium becomes higher than in the right atrium leading to the septum primum being pushed against the septum secundum. They fuse and form a barrier.
Give some examples of ways an atrial septal defect can be caused
- excessive resolution of septum primum
- short septum primum
- absence of septum secundum
- absence of both septum secundum and septum primum
What is hypoplastic left heart syndrome?
This occurs when the left ventricle is underdeveloped, resulting in atresia and limited flow
What are the two components of the ventricular septum?
Muscular and membranous
What is the primary interventricular foramen?
A small gap between the ventricles that is closed by the interventricular septum
What effect would transposition of the great arteries have on the appearance of the baby?
The baby would have cyanosis
What is the tetralogy of Fallot?
1) pulmonary stenosis
2) ventricular septal defect
3) right ventricular hypertrophy
4) over-riding aorta
