Cardiac Embryology Flashcards
In what direction does the heart rotate during embryological development/
Left
Label the structures on the diagram
Where do blood vessels develop?
At what stage of development is this embryo?
What do the umbilical vessels communicate with?
Label the blood vessels on the diagram
In the extraembryonic mesoderm
Week 3
Umbilical vessels communicate with:
- Developing fetal circulation
- Developing placenta
Label the features on the cardiac mesoderm
At what stage of development is this embryo?
What are angiogenic cell clusters?
Angiogenic cell clusters are collections of angiogenic cells which are developing into blood vessels.
- Form paired angiogenic cords
- Cords canalise to form paired endochondral heart tubes
Embryo in image is in week 3 of development
When does the embyronic heart begin beating?
When does blood flow begin?
Heart starts beating day 22-23
Blood flow begins week 4
What is the role of neural crest cells?
Neural crest cells from the developing brain and spinal cord migrate away from the developing central nervous system.
Involved in the development of parts of the heart
Label the structures on the embryonic disc
Where is the heart tube?
What occurs during longitudinal folding?
The brain, mouth and heart are moved into ‘adult’ position:
- The brain develops quickly and pushes itself above the mouth region
What does the septum transversum become?
Fibrous pericardium and part of diaphragm
What happens to the paired heart tubes during lateral folding?
They are brought together and fuse in the midline to form a large singular tube
Venous inflow enters and flows through the tube into the aortic arches
Where do the aortic arches sit?
Pharyngeal arches
What anchors the developing heart tube to the future diaphragm (septum transversum)
Label the developing structures on the diagram
Vitelline veins
What do the dilations of the heart tube become?
Label them on the diagram
Bulbus cordis
- = aortic vestibule of left ventricle
- = conus arteriosis of left ventricle
Truncus arteriosus
- = Ascending aorta
- = Pulmonary truk
Ventricle
- = trabecular walls of left and right ventricles
Atrium
- = auricles/pectinate walls of left and right atria
Sinus venosus
- = Coronary sinus
- = Smooth wall of right atrium
How does the heart tube split to form right and left sides of the heart?
- Endocardial cushion develops and grows into a septum separating the heart tube into 2 sections longitudinally
What develops from the future left atrium section of the heart tube?
Pulmonary veins
Where are the rough atrial walls derived from embryologically?
What are the smooth walls formed from?
Rough atrial walls: embryological atrium
Right smooth atrial wall: right horn of the venous sinus
Left smooth atrial wall: formed from its growth into the pulmonary veins
What causes the heart tube to fold?
Describe this process
Folds due to the fixed position of the aortic arches and venous input.
- Bulbus cordis grows quickly and moves infero-anteriorly to the right
Describe the vascular shunts in the embryonic heart
Right to left shunts exist to bypass the lungs which are not fully developed.
Shunt between right and left atria
Shunt between pulmonary trunk and aorta
How does dextrocardia occur?
What is it?
Dextrocardia= adult heart on the right side instead of left.
Occurs when bulbus cordis folds to the left and ventricles form to the right
How are the developing atria connected to the ventricles?
Via the atrioventricular canal
Where do the bicuspid and mitral valves grow?
Within the atroventricular canal
How is the atrioventricular canal separated?
By endocardial cushions that grow from anterior to posterior and meet in the middle to separate right and left AV canals
How does atrial septation occur?
- Septum primum develops and grows towards endocardial cushion.
- Before it reaches the cushion, holes form (foramen secondum)- this maintains right to left shunt.
- Muscular septum secondum then grows towards cushion
- This forms the foramen ovale through which blood is shunted right to left.
Describe the pressure differences in the right and left sides of the heart in utero compared to a neonate.
Why is there a difference?
In utero:
- High pressure right side of heart
- Lower pressure in left side of heart
- Due to:
- Lungs filled with fluid
- High pulmonary vascular resistance
- More blood is entering the right atrium than the left
- Blood shunted through foramen ovale
Post-natal:
- Lower right sided pressure than left
- Due to:
- Lungs drained and functional
- Low pulmonary vascular resistance
- Greater pulmonary blood flow
- More blood in left atrium
- Valve of foramen ovale closes on first breath
When do tissues of the foramen ovale fuse?
What is it called when they don’t properly fuse? When can this be a problem?
How can this defect be detected?
Usually fuse several months after birth
Failure to properly fuse = probe-patient foramen ovale
Can become a problem in situations where right sided heart pressure increases over left- for example during the valsalva manouvre
- Increases possibility of TIA and stroke (clots in the right side can be pushed over to the left and enter the systemic circulation)
Microbubble test is used to detect defects (ultrasound)
Where can atrial septal defects form?
Are they always symptomatic?
- In the septum/foramen primum
- In the septum/foramen secondum
- In the endocardial cushion
Some symptomatic, some not
Some close during growth without the need for surgical intervention
In what direction would the blood be shunted in an atrial septal defect after birth?
Why is a small atrial septal defect not a cyanotic congenital cardiac defect?
Left to right (pressure in left side higher after birth than right)
Cyanosis woud not occur as blood shunted would be re-circulated around the lungs
How does ventricular septation occur?
Ventricular septum grows towards endocardial cushion from ventricular floor- remains incomplete in upper region
Completed in the upper (cranial) region by membranous downgrowth of bulbar ridges and endocardial cushion.
- Membranous tissue also separates the aorta and pulmonary trunk
Where do ventricular septal defects most commonly occur?
In the membranous part of the septum
How is the ventricular outflow separated (into aorta and pulmonary trunk)?
At what stage of embryological development does this occur?
Membranous septum forms in truncus arteriosis and bulbus cordis which spirals (spiral septum) due to the turbulent flow of blood.
Grows down to meet the muscular part of the ventricular septum
What would be the result of a failure of bulbar ridge formation?
Failure of bulbar ridge formation
- Ventricular septal defect AND
- Common arterial outflow
- Results in mixing of oxygenated and deoxygenated blood as both right and left ventricles pump blood into the aorta and pulmonary trunk
- Cyanosis
What would be the result of unequal separation of aorta and pulmonary trunk by the spiral septum?
Can result in small pulmonary trunk which increases vascular resistance (may cause cyanosis)
- This leads to right ventricular hypertrophy
OR a small aorta (aortic stenosis)
These conditions often accompanied by ventricular septal defects
What is transposition of the great vessels?
Congenital heart defect producing 2 isolated circulations (right ventricle pumps into the aorta and the left ventricle pumps blood into the pulmonary trunk)
Often accompanied by ventricular septal defects which are beneficial in this case.
Patent ductus arteriosus can also help to mix blood
What is tetralogy of fallot?
Multiple congenital cardiac defects occuring together:
- Pulmonary stenosis
- Right ventricular hypertrophy
- Ventricular septal defect
- Over-riding aorta (aorta receives blood from left and right ventricles)
Caused by failure of formation of the ventricular septum, unequal separation of the aorta and pulmonary trunk
Cyanotic condition
Name some cyanotic congenital cardiac defects
- Tetralogy of fallot
- Transposition of great vessels
- Truncus arteriosus defects
- Critical pulmonary stenosis
Name some non-cyanotic cardiac defects
- Atrial septal defect
- Ventricular septal defect
- Patent ductus arteriosus
