3. CVS Development Flashcards
Describe the formation of the primitive heart tube.
Cariogenic field is created during gastrulation, at the cranial end of the embryo before folding.
Endocardial tubes develop within cardiogenic field.
Endocardial tubes fuse together during embryonic folding, creating the primitive heart tube.
What are the segments of the primitive heart tube?
truncus arteriosus bulbus cordis ventricle atrium sinus venosus
What is the importance of ‘looping’ and what triggers it?
As the tube elongation is confined to the pericardial space, it bends on itself. This places the atria above and behind the primitive ventricles.
Endocardial tubes develop within the cardiogenic field in week ____.
3
What does the RA develop from?
Most of primitive atrium
Part of sinus venosus
What does the LA develop from?
Part of primitive atrium
Absorbs proximal parts of pulmonary veins
Why is the RA rough lined yet the LA is smooth lined?
Primitive atrium has a rough lining, and makes up most of the RA. Whereas the pulmonary veins are smooth and make up the LA.
What is the main difference between the fetal circulation and the mature circulation?
Fetal lungs do not work
Oxygenation and CO2 removal occurs at the placenta
How is the circulatory system adapted to meet both metal and mature requirements?
Shunts in fetal circulation which are reversible at birth.
3 fetal shunts are used to by-pass which areas?
- By-pass liver after placenta
- Shunt from RA to LA (by-pass RV and lungs)
- Shunt from PT to aorta (by-pass lungs)
Why is it important that a small amount of blood enters the RV in the fetus?
Ensure normal development of the ventricle.
Shunt from pulmonary trunk to aorta to avoid lungs.
Name the 3 fetal shunts.
- Ductus venosus (by-pass liver)
- Foramen ovale (RA to LA)
- Ductus arteriosus (PT to A)
Describe how the shunts are shut at birth.
At first breath, LA pressure> RA pressure which pushes the septum premium against the septum secundum to close the foramen ovale.
Ductus artiosus contracts and closes
Placental removal causes ductus venosus to close.
How is the early arterial system arranged?
Bilateral symmetrical system of arched vessels
Which arch is remodelled to give the ‘pulmonary arch’?
6th arch gives R and L pulmonary artery
Which arch is remodelled to give the arch of aorta and subclavian artery?
4th arch
Which nerve becomes wrapped around the ductus arteriosus shunt during the caudal shift?
Left recurrent laryngeal nerve
What is patent ductus arteriosus (PDA)?
Ductus arteriosus remains open due to failure of physiological closure.
Blood will shunt L to R from aorta into PT after birth.
What forms an essential scaffold to both atrial and ventricle septum development?
Endocardial cushions - neural crest cells which migrate into the developing heart and allow chamber development.
Describe the formation of the atrial septum and foramen ovale.
- Septum primum extends down from primitive atrium.
Ostium primum at its free edge fuses with the cushions
Ostium secondum remains. - Septum second extends up from cushions. This has a hole which doesn’t line up with ostium secondum, creating a shunt called the foramen ovale.
What direction does the foramen ovale shunt blood?
R to L in fetus
Suggest mechanisms which could lead to atrial septal defect.
Septum primum reabsorbed or too short
Septum secondum too small
What is hypoplastic left heart syndrome?
Underdeveloped left ventricle
What could cause hypoplastic L heart syndrome?
- Defect in development of mitral and aortic valves, causing atresia and limiting flow to LV.
- ostium secondum too small, so R to L flow inadequate.
What are the 2 components of the ventricular septum?
Muscular and Membranous
Describe how the ventricular septum is formed.
Muscular portion grows upwards towards endocardial cushions, leaving a small gap - primary inter ventricular foramen.
Membranous portion grows down from cushions to close the foramen.
Which component of the ventricular septum is usually the cause of a ventricular septal defect?
Membranous
What would be the effect of a ventricular septal defect?
L to R shunt
How is a spiral septum in the outflow tract developed?
Endocardial cushions in the truncus arteriosus grow towards each other and twist to form a spiral septum, separating the outflow tracts.
