Embryology 1 Flashcards
From what embryonic tissue is the circulatory system derived?
The lateral plate splanchnic mesoderm
Where are the first blood vessels found?
In the walls of hte tolk sac, allantois, connecting stalk and chorion.
How are the two primitive heart tubes formed?
Aniogenic cell islands coalesce in the lateral plate splanchnic mesoderm
Then migrate towards the midline
Then become paired angioblastic cords before becoming heart tubes
The 2 heart tubes form to make one primitive heart tube, what are its sections?
From cranial to caudal:
- Truncus Arteriosus
- Bulbus Cordis
- Primitive Ventricle
- Primitive Atrium
- Sinus Venosus
Describe the structure of the sinus venosus/
Two horns Each horn divides to drain blood from 3 areas: - Yolk sac via vitelline vein - Placenta via umbilical vein - Embryo's body via common cardinal vein
What happens above the truncus arteriosus?
The top of the TA forms the aortic sac which divides into two horns each with 6 arches that terminate in a R & L dorsal Aorta
How does the heart tube become the shape of the adult heart?
The BC and ventricle grow faster than the rest of it causing it to loop to the right forming a caridac (bulboventricular) loop.
How does dextrocardia occur?
The heart tube loops to the left instead of right so it ends up facing the right.
What is the final fate of the bulbus cordis?
The Bc forms the right ventricle and parts of the outflow tracts (aorta & pulmonary trunk)
What is the adult form the primitive ventricle?
the left ventricle
What does the primitive atrium becomes?
Left atrium and parts of right.
What does the sinus vensosus become?
The SVC and the right atrium
How is the common atrioventricular canal seperated into left and right?
By formation of endocardial cushions
In short how are the atria seperated?
By the formation of two adjacent septa each with a foramen that eventually close after birth
What are the two septa and foramen in the atria?
Septum Primum - Foramen secundum
Septum Secundum - Foramen Ovale
What are the remains of the foramen ovale left behind in an adult?
The fossa ovalis in the interatrial septum
What is the function of the foramen ovale?
To allow blood to bypass the lungs passing straight through a valve from right to left atria.
Whats another name for foramen?
Ostium
To which side is each atrial septum?
The septum secundum is to the right of the septum primum
What is non closure of the foramen called?
Atrial Septal Defect (ASD)
What are the types of ASD?
1) Foramen Secundum defect
2) Endocardial cushion and foramen primum defects
3) Sinus Venosus defect
4) Common Atrium
What is the foramen primum?
An inferior foramen between the septum primum and endocardial cushion prior which closes prior to septum secundum growth.
What seperates the left and right ventricles?
A muscular interventricular septum at the base and membranous interventricular septum at the top.
How does the muscular interventricular septum form?
From the bottom of the primitive ventricle leaving an interventricular foramen at the top
How does the membranous interventricular septum replace the interventricular foramen?
The aorticopulmonary septum rotates & fuses with the muscular septum forming the membranous one
How common is Ventricular Septal Defect?
VSD is the most common congenital heart disease (~25% of all CHD)
Most ocmmon in men
MEmbranous is more common than muscular
What happens to small VSDs?
up to half close spontaneously
What sections of the heart tube give rise to the aorta/pulmonary trunk?
The bulbus cordis (BC) and Truncus Arteriosus (TA)
How does the aortiocopulmonar (conotruncal) septum form?
1) Mesenchymal cells from the neural crest proliferate in the BC & TA walls
2) Bulba & Truncal ridges form
3) Ridges connect formin the septum.
What happens to the aorticopulmonary septum after its formed?
It twists 180degress due to streaming past of blood causing the overlap of the aorta & Pulmonary trunk
What gives rise to the AV node and bundle of his?
Cells of the AV canal and the Sinus Venosum
What gives rise to the SA node?
Cells of the Primordial atrium and Sinus Venosum
What happens when conducting tissue is abnormal?
Cot death or Sudden Infant Death Syndrome (SIDS)
From what structure is the pericardium derived?
The intra-embryonic coelom
What tissue gives rise to the parietal and fibrous pericardium?
Somatic Mesoderm
What tissue gives rise to the visceral pericardium?
Splanchnic Mesoderm
Which CHDs are most common in women?
ASD & PDA (Patent Ductus Arteriosus)
What causes PDA?
The mother having a rubella infection while pregnant
What often causes septal defects?
Maternal alcohol abuse
Name some chromosomal CHDs
Downs Syndrome
Turners Syndrome
What are the causes of CHDs?
Generally multifactorial: Maternal Infection Maternal substance abuse Genetics Maternal drug/radiation treatments
What is transposition of the great vessels?
A congenital heart disease.
The pulmonary trunk no longer crosses the base of the aorta, instead they run parallel. And there is PDA.
A common cause of cyanotic disease in newborns
What is associated with Transposition of the Great Vessels?
ASD/VSD
What does PDA allow?
Exchange of blood between deoxygenated pulmonary & oxygenated systemic circulation
What causes Transposition of the great vessels?
Either:
Failure of the aorticopulmonary septum to spiral
Defective Migration of neural crest
What is tetralogy of fallot?
A 4 part congenital heart disease.
- Pulmonary stenosis
- VSD
- Dextroposition of Aorta (Aorta right over the VSD)
- Right ventricular Hypertrophy
What is the consequence of dextroposition of the aorta in a case of Tetralogy of Fallot?
The Aorta recieves blood from both ventricles so its not properly oxygenated
What causes Tetralogy of Fallot?
An unequal division of the conus due to anterior displacement of the aorticopulmonary septum
