Development of the heart Flashcards
Understand the basic development of the heart. Describe how fetal circulation differs from that of the neonate. Understand the circulatory adaptations at birth. Describe some common congenital abnormalities of the heart.
What is the special about the development of the heart?
It is one of the earliest organs to develop, differentiate and function.
What does the heart develop from at day 18?
From the cranial end of the neural tube from cardiogenic mesoderm (lateral plate)
What does the cardiogenic mesoderm contain?
Blood islands of haemangioblasts and myoblasts.
What happens at 20 days?
The angioblast cell clusters form left and right endocardial tubes which are continually dorsally with the aorta and caudally with the vitello-umbilical vein.
What happens at 21 days?
The left and right endocardial tubes fuse together into a primitive heart tube.
What happens at 22 days?
The heart starts to beat and more structures begin to form such as: sinus venosus, paired primitive atria, atrioventricular sulcus, primitive ventricle, interventricular sulcus, bulbus cordis
What is the function of the sinus venosus?
Inflow
What is the function of the atrioventricular sulcus?
To separate the atria from the primitive ventricle
What is the function of the primitive ventricle?
becomes the left ventricle
What is the function of the interventricular sulcus?
Divides primitive ventricle from the bulbus cordis
What are the parts of the bulbus cordis?
Cranial - truncus arteriosus
Caudal - conus cordis
LV - aortic vestibule
RV - conus arteriosum
What is heart looping and when does it happen?
At 22 days after the structures have formed the heart lengthens but the ends are fixed so it is forced to bulge and twist in the pericardial sac
How does the septum form in the atrio-ventricular canal and when?
At 28 days 2 mesenchymal tissue swellings appear from the canal walls to form endocardial cushions. They grow and fuse dividing the canal into right and left.
What is the septum primum
On day 28 the septum primum appears (a tissue crescent) and grows from the dorsal atrial wall to the endocardial cushion.
How do the atria partition?
Before the septum primum is formed, the foramen ovale is open as the right atrium has a higher pressure. However at birth the left atrial pressure increases as the pulmonary vein empties into it and the septum primum is forced against the septum secundum so that they fuse together closing the foramen ovale and forming the common atrial septum.
How do the ventricles form and when?
At 28 days the interventricular septum develops form the apex of the primordial ventricle and grows towards the atrio-ventricular canal. The interventricular foramen then closes when on the 7th week when the septa fuses.
How do the aorta and pulmonary trunk partition?
2 swellings grow from the truncus arteriosus to form 2 spiral ridges which then twist and fuse forming a spiral aortico-pulmonary septum.
What are the main differences in fetal circulation compared to that of a neonate?
Fetal haemoglobin vs. adult haemoglobin Ductus venosus Ductus arteriosis Foramen ovale The RV pumps 2/3 of the CO instead of the LV
What is the purpose of the ductus venosus?
Shunts blood from the umbilical vein to the IVC to bypass the liver.
What is the purpose of the ductus arteriosus?
Shunts blood from the pulmonary trunk to the aorta to bypass the lungs.
What is the purpose of the foramen ovale?
Shunts blood from the right atrium to the left atrium to bypass the pulmonary circulation.
How does blood pass from the placenta to the baby?
Deox blood travels from the baby to the placenta via the umbilical arteries whilst ox blood is passed to the baby via the umbilical veins.
Which circulatory adaptations occur at birth?
Ductus venosus becomes the ligamentum venosus.
Umbilical veins becomes the ligamentum teres
Ductus arteriosus becomes the ligamentum arteriosus. Foramen ovale becomes the fossa ovalis.
Umbilical arteries constrict partly but some stay patent to supply the bladder.
How does the foramen ovale close?
There is decreased IVC and placenta flow so the RA pressure. Pulmonary flow increases so LA pressure increases. The lung also expands reducing pulmonary vascular resistance.
How does the ductus arteriosus close?
Bradykinins help mediate it, paO2 increases and pulmonary vascular resistance is decreased?
How may a truncus arteriosus become persistent?
Prostaglandin E2 may enable it to reopen.
How do you treat persistent truncus arteriosus?
Prostaglandin E2 inhibitor such as ibuprofen or if this does not work need to clip it during surgery to close it.
What cyanotic congenital abnormalities of the heart are there?
Teratology of fallot
Persistent truncus arteriosus
Transposition of the great vessels
What is teratology of fallot?
Ventricular septal defect leading to RV hypertrophy and RV stenosis resulting in cyanosis.
What does persistent truncus arteriosus lead to?
Single artery supply between the pulmonary trunk and aorta so blood mixes leading to cyanosis
How can transposition of the great vessels cause problems?
The septum in the trunk doesn’t follow its correct spiral course and instead grows straight down, this can also mean the ductus arteriosus stays open.
What acyanotic congential abnormalities are there?
atrial septal defects
ventricular septal defects
persistent ductus arteriosus
coarctation of the aorta
How can atrial septal defects occur?
Septum primum and septum secundum mistakes
What symptoms arise with ASD?
fatigue, exercise intolerance, dyspnea during exercise
What are some key features of VSD?
Most common type of heart abnormality
90% are in the membranous septum and 10% are in the muscular septum
Where can the aorta be constricted in coarctation? What is the difference in these?
Pre-ductal if below the ductus arteriosus which allows flow.
Post-ductal if above the ductus arteriosus meaning collateral flow is required for proper perfusion of the body and legs.
What can coarctation of the aorta lead to?
Hypertension, left ventricular hypertrophy
What is the treatment for coarctation of the aorta?
Balloon angioplasty
