S3 Development of CVS Flashcards
What effect does folding (lateral and cephalocaudal) of the embryo have on the early development of the heart?
Lateral - creates a heart tube
Cephalocaudal - brings the tube into the thoracic region
What are the 6 sections of the primitive heart tube?
- Aortic roots
- Truncus arteriosus
- Bulbus cordis
- Ventricle
- Atrium
- Sinus venosus
Describe the folding and looping of the primitive heart tube.
- The tube elongates
- It runs out of room due to the pericardial sac being a set size
- So the tube twists and folds (in a regular and predictable way)
- This places the inflow and outflow in the correct orientation in respect to each other
- The atrium and ventricle expand
How is the transverse pericardial sinus formed?
Folding so the arteries/outflow are in front of the veins/inflow
How does the sinus venosus develop?
- The right and left sinus horns are initially equal sizes
- The venous return shifts to the RHS, the left sinus horn recedes
- The right sinus horn is absorbed by the enlarging right atrium
(Producing superior and inferior vena cava)
How does the atria (right and left) develop?
Right atrium - develops from most of the primitive atrium, sinus venosus and receives venous drainage from the vena cava and coronary sinus
Left atrium - develops from a small section of the primitive atrium, also absorbs proximal parts of the pulmonary veins and receives oxygenated blood from the lungs
How does the oblique pericardial sinus form?
Formed as the left atrium expands absorbing the pulmonary veins (between the heart and pericardial sac)
What is used in the foetus given the lungs don’t work to move oxygenated blood from the right side to the left side of the heart?
Shunts
What are the 3 foetal circulatory shunts? What does each bypass?
- Ductus venosus - liver
- Foramen ovals - right ventricle and lungs
- Ductus arteriosus - lungs
What is the mature circulatory system (after birth)?
- Right atrium
- Right ventricle
- Pulmonary trunk
- Lungs
- Pulmonary veins
- Left atrium
- Left ventricle
- Aorta
- Body
- Right atrium
What is the fetal circulatory system?
- Oxygenated blood from mother
- Placenta
- Bypass the liver - ductus venosus
- Inferior vena cava
- Right atrium
- Bypass the right ventricle and lungs - foramen ovale.
A small amount of blood drains into the right ventricle from the right atrium (to keep the right ventricle developing normally) to the pulmonary trunk, bypass the lungs - ductus arteriosus, aorta - Foramen ovale to the left atrium
- Left ventricle
- Aorta
- Body
- Placenta
- Deoxygenated blood back to mother
What happens after birth that converts the circulatory system from the fetal to the mature?
- respiration begins
- the left atrial pressure increases causing the foramen ovale to close
- the ductus arteriosus contracts
- placental support is removed
- the ductus venosus closes
What are the 4th aortic arch derivatives?
- right - proximal part of the right subclavian artery
* left - arch of aorta
What are the 6th aortic arch derivatives?
- right - right pulmonary artery
* left - left pulmonary artery and ductus arteriosus
What is the left recurrent laryngeal nerve hooked around?
The 6th aortic arch, hooked around the the shunt (ductus arteriosus)
What is PDA (in terms of congenital heart diseases)?
Which direction is blood shunted?
Patent ductus arteriosus
Failure of the physiological closure of the ductus arteriosus so there’s persistent communication between the descending aorta and the pulmonary artery
Left to right (down pressure gradient)(aorta to pulmonary artery)
What does the atrioventricular canal defect link?
Links the primitive atrium and ventricle
What is the interarterial and interventricular septum?
The interarterial septum - separates atrium into left and right
The interventricular septum - separates ventricle into left and right
What does the septation of the ventricular outflow tract separate?
The pulmonary trunk and aorta
What are the endocardial cushions?
Divide the heart into right and left channels producing an atrioventricular junction
How does atrial septation occur?
- Septum primum grows downwards towards the fused endocardial cushions
- The ostium primum is the hole present before the septum primum fuses with the endocardial cushions
- Before the ostium primum closes, a second hole, the ostium secundum appears in the septum primum
- The septum secundum starts to grow forming a hole called foramen ovale
- The right atrium to left atrium shunt is created
- The pressure created forces the ‘leaves’ apart
What is the name of the adult remnant of the foramen ovale?
Fossa ovalis
What is the pressure gradient between atria before and after birth?
Before - right atrium to left atrium
After - left atrium to right atrium
What does the pressure gradient, left to right atria, cause to happen to the septums?
The septum primum is pushed against the septum secundum, closing the shunt
What are the three types of atrial septal defect?
- Ostium secundum defect
- Septum primum defect - resorbed or too short
- Septum secundum defect - too small
What is hypoplastic left heart syndrome?
Underdevelopment of the left side of the heart (left ventricle)
The exact causes of hypoplastic left heart syndrome aren’t known but what are 2 possible causes?
- Defect in the development of the mitral and aortic valves results in limited flow and absence/narrowing of the ‘passage’
- Ostium secundum is too small
So right to left flow is inadequate in utero
Leading to an underdeveloped left side of the heart
How does ventricular septation occur?
- Start with a single ventricular chamber
- The ventricular septum forms which has 2 components, muscular and membranous
- The muscular component forms most of the septum and grows upwards towards the fused endocardial cushions
- A small gap is left - the primary interventricular foramen
- The membranous component of the interventricular septum fills the primary interventricular foramen/gap
What is the membranous component of the interventricular septum formed by?
Connective tissue derived from the endocardial cushions
What is most commonly defective in ventricular septal defect?
The membranous component of the interventricular septum
How does septation of the outflow tract occur?
- Endocardial cushions appear in the truncus arteriosus
- Grow towards each other and twist around each other
- For a spiral septum - aorticopulmonary septum
What sort of congenital birth defects can you get, generally?
- Structural defect (of chambers or vasculature)
- Obstruction
- There is communication between pulmonary and systemic circulations
- Shunting not closed off/reversed properly after birth
What generally causes congenital birth defects?
- Genetic
- Exposure to chemicals/drugs/infectious agents
- Unexplained
What is transposition of the great arteries?
When the aorta rises from the right ventricle and the pulmonary trunk arises from the left trunk
What does transposition of the great arteries cause?
Cyanosis (blueish discolouring of skin due to poor circulation)
What is transposition of the great arteries likely to be related to?
Related to the development of the aortic and pulmonary valves
What is tetralogy of Fallot?
A large ventricular septal defect
- aorta sits between the left and right ventricles/overriding aorta
- pulmonary trunk stenosis - right ventricular outflow tract obstruction
- right ventricular hypertrophy
- conotruncal septum formation is defective
What is the importance of neural crest cells?
They create the endocardial cushions
