Flashcards in Embryology of the CVS Deck (29):
What are the main stages of the development of the CVS?
1. Development of primitive heart tube
2. Looping of the heart tube
3. Atrial and ventricular septation
4. Development of the outflow tract
What occurs in the 3rd week of development?
Lateral plate splanchnic mesoderm forms circulatory system (and other viscera).
How do angiogenic cell islands form the two primitive heart tubes?
Angiogenic cell islands collect in the lateral plate splanchnic mesoderm, move towards the midline and coalesce to form the two primitive heart tubes
When does the premordial heart start to function?
It starts to function at the beginning of the 4th week.
Where do blood vessels first appear?
- They first appear in the wall of yolk sac, allantois, connecting stalk and chorion.
- Appearance of paired endothelial strands (angioblastic cords) appear in the cardiogenic mesoderm at 3rd week
What do Angioblastic cord become?
Angioblastic cords canalise to form heart tubes.
-Tubular heart joins blood vessels in other areas to form primordial cardiovascular system
What is the pericardium formed from?
- It is derived from intra-embryonic coelom.
- Parietal layer of serous pericardium & fibrous pericardium are formed from somatic mesoderm.
- Visceral layer of serous pericardium is derived from splanchnic mesoderm.
In the embryo, what way does the cranial end (arterial) face?
Cranial ends faces towards the head of the embryo
In the embryo, what way does the caudal end (venous) face?
Caudal end faces towards the tail of the embryo
In the fused primitive heart tube what way do the bulbus cordis and ventricle face?
Bulbus cordis folds towards the right so ventricle moves to the left!
Features of the sinus venosus (venous end)
- Two horns: right and left
- Each horn gets venous blood from: yolk sac(=vitelline v.), Placenta(=umbilical v.), Body of the embryo (=common cardinal v.)
Features of the Truncus arteriosus (arterial end)
- Continuous cranially with the aortic sac.
- Aortic arches arise from the aortic sac.
- Aortic arches terminate in the dorsal aorta.
How does the cardiac (Bulboventricular) loop form?
Bulbus cordis and ventricle grow faster than other regions forming a U-shaped
Describe dextrocardia (abnormal cardiac looping)
- Heart tube loops to the left side (instead of right), thus coming to lie facing the right (=dextro).
- Dextrocardia can be associated with situs inversus (transposition of viscera)
What are the 2 forms of partitioning of Primordial heart?
1. Endocardial cushion formation - separates right atrium + ventricle from left atrium + ventricle to form L&R AV canals.
2. Septum formation- separates right atrium from left atrium + right ventricle from left ventricle.
Clinical - e.g. atrial septal defect (ASD) & ventricular septal defect (VSD)
Partitioning of primitive atrium into left & right atria
- Starts towards the end of the 4th week.
- Two septum and two foramina (openings) develop during the partition:
1. Septum primum & foramen primum
2. Septum secundum & Foramen secundum
When does the septum primum form?
- End of 4th week, sickle shaped crest grows from roof of atrium: Septum Primum.
- Septum primum growth generates foramen primum
What is the ostium primum?
Opening between septum primum & endocardial cushion.
Formation of Foramen secundum
Foramen secundum is formed at the upper end of septum primum (due to cell death).
- Foramen secundum is opening in septum primum.
Formation of septum secundum
Septum secundum (new fold) forms on the right of septum primum.
- It grows down and overlaps the foramen secundum.
- But septum secundum is incomplete - perforated by oval foramen (foramen ovale).
What is Foramen ovale?
Foramen ovale is opening in septum secundum.
What is the role of oval foramen before birth?
- Allows most of the blood to pass from the right atrium to the left atrium (non-functioning lung)
- Prevents the passage of blood in the opposite direction.
What is the role of oval foramen after birth?
- Normally closes (increased pulmonary blood flow and shift of pressure to the left atrium)
- Septum primum (= valve of oval foramen) fuses with the septum secundum
- Oval fossa (fossa ovalis) of adult heart is a remnant of foetal oval foramen
- Non closure results in Atrial Septal Defect (ASD) – “Hole in the heart”
What is Atrial Septal Defect (ASD)?
- Common congenital heart anomaly
- More common in females than in males
- Common form: patent foramen ovale.
What are the 4 clinically significant types of ASD?
1. Foramen secundum defect
2. Endocardial cushion defect with foramen primum defect
3. Sinus venosus defect
4. Common atrium
- The first two types are more common
Steps in partitioning of primitive ventricle
1. Muscular ventricular septum forms. Opening is called interventricular foramen.
2. Bottom of spiral aorticopulmonary septum fuses with muscular ventricular septum to form membranous interventricular septum, closing interventricular foramen. (Aorticopulmonary septum divides bulbis cordis and truncus arteriosus into aorta and pulmonary trunk).
3. Growth of endocardial cushions also contributes to membranous portion of the interventricular system.
When does the partitioning of bulbus cordis (BC) and truncus arteriosus (TA) occur?
During the 5th week of development.
- Aorticopulmonary septum divides BC and TA into aorta and pulmonary trunk
Features of Ventricular Septal Defects (VSD)
- Most common type of CHD (congenital heart disease) – 25% of defects
- Common in males
- Can appear in any part of septum
Small VSDs close spontaneously (30 -50%)
- Membranous type of VSD is most common!!