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Mobeen Syed M.D, MS Graduated from King Edward Medical University. Entrepreneur, Medical Educator, CEO and founder of Drbeen corp.
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This video presents
STUDY NOTES:
VENTRICLES & AORTICOPULMONARY SEPTUM
DEVELOPMENT OF INTERVENTRICULAR SEPTUM & PARTITION OF PRIMITIVE VENTRICLES
Embryonic time line of IV SEPTUM DEVELOPMENT: begins in the late 4th week and beginning of 5 th week. By the end of 4th week, the primitive ventricle is one single chamber which receives blood from the atria via the divided atrioventricular canal. Then there's also a single aorticopulmonary trunk opening into primitive ventricles which forms the outflow tract. At this point aorticopulmonary trunk is formed of bulbus cordis and truncus arteriosus and it provides the outflow tract for the primitive ventricles. During later parts of the development the bulbus cordis gets incorporated into the right and left ventricles. Upon incorporation, on the right side the bulbus cordis forms the infundibulum of the right ventricle, and on the left side it forms the vestibule of the left ventricle. Hence, bulbus cordis forms the smooth outflow tracts of the ventricles on either side. Truncus arteriosus on the other hand develops into forming aorta and the pulmonary trunk on the left and the right sides respectively.
Adult IV septum consists of two parts, a muscular part (derived from the myocardial cells) which forms the majority of the septum, and a relatively thin membranous part which forms the superior aspect of the IV septum which is part of the outflow tract.
By the early 5th week, the muscular IV septum develops as an IV septal ridge from the floor of the primitive ventricle near the apex of the heart. This interventricular septal ridge ascends towards the atrioventricular canal, and thereby partially divides the primitive ventricle into left and right ventricles. The IV septal ridge extends towards the atrioventricular canal but it does not reach it, hence giving rise to a gap or defect which is referred to as interventricular foramen (IV Foramen). Thus the IV foramen is formed by the concave upper edge of the IV septum which gives rise to a gap through which shunting of blood between the right and left ventricles occurs.
The membranous IV septum descends downward from the AV canal and fuses with the muscular IV septum thereby completely obliterating the IV foramen. The membranous part of IV septum is contributed by the following:
CLINICAL DISORDERS ASSOCIATED WITH INTERVENTRICULAR SEPTUM DEVELOPMENT
Other than with ventricular septal defects, Eisenmenger complex can also present along with atrial septal defects and patent ductus arteriosus. It's important to remember that post birth, right to left shunts result in early cyanosis. Whereas, "left to right" shunts result in late cyanosis. Children suffering from late cyanosis are referred to as blue kids in contrast to the newborns which present with cyanosis at birth and are referred to as blue babies.
DEVELOPMENT OF AORTICOPULMONATY SEPTUM
Aorticopulmonary trunk arises from the primitive ventricles and serves as an outflow tract for the primitive ventricle. An aorticopulmonary septum forms within the aorticopulmonary trunk, thereby subsequently dividing it into the aorta & pulmonary trunk. Aorticopulmonary septum is formed by the migration of neural crest cells into the c conotruncal and bulbar ridges of the truncus arteriosus. These neural crest cells grow in a spiral fashion and fuse to form aorticopulmonary septum. As the aorticopulmonary septum descends as part of its growth, it spirals in such a fashion that aorta becomes the left ventricular outflow tract and the pulmonary trunk becomes the right ventricular outflow tract. As mentioned earlier, as part of its descent the aorticopulmonary septum contributes to the development of the membranous part of interventricular septum and therefore helps fill in the opening formed by the interventricular foramen.
DEFECTS IN THE DEVELOPMENT OF AORTICOPULMONARY SEPTUM result due to defects in migration of neural crest cells into the truncus arteriosus. At birth these aorticopulmonary septal defects always present with some cyanosis due to right to left shunting of the blood. Following are the congenital abnormalities associated with development of AP septum:
Due to the presence of a ventricular septal defect, and a stenosed pulmonary outflow tract which presents with greater resistance to blood flow, there's a right to left shunting of the blood. This right to left shunting results in cyanosis because the blood leaving the heart via the aorta is mixed with deoxygenated blood from the right ventricle. A very important point to remember and which is highly tested as well is that, squatting tends to improve this cyanosis. This is because squatting tends to increase systemic vascular resistance or afterload, which tends to decrease right to left shunting of the blood via the VSD and thereby helps improve the cyanosis.
Clinically, ToF presents with a harsh systolic ejection murmur which can be auscultated at middle to left sternal border. This murmur occurs due to presence of right ventricular outflow tract obstruction.
KEY:
ASD= Atrial septal defect
VSD= Ventricular septal defect
PDA= Patent ductus arteriosus
PFO= Persistent foramen ovale
AP= Aorticopulmonary
IV= Interventricular
In this video we will learn about :
1. Development of inter ventricular septum.
2. Development of aorticopulmonary septum.
3. Patent truncus arteriosus.
4. Transposition of great vessels.
5. Tetrology of fallot.