Embryology 1 Flashcards
What are the 4 major stages in heart development?
- Primitive heart tube
- Heart looping
- Atrial and ventricular septation
- Outflow tract septation
When does heart development begin?
3rd week
What forms the circulatory system?
Lateral plate mesoderm
How are the 2 primitive heart tubes formed?
Angiogenic cell islands collect in the lateral plate mesoderm, move towards the midline and coalesce
What is the first major system to function in the embryo?
Cardiovascular system
When does the primordial heart start to function?
Beginning of 4th week
Why does the cardiovascular system begin to function so early?
The embryo is rapidly growing and nutrition by diffusion is not enough to satisfy the growing embryo
Where do blood vessels first appear?
- Wall of the yolk sac
- Allantois
- Connecting stalk
- Chorion
What are angioblastic cords?
Paired endothelial strands
When do angioblastic cords appear?
3rd week
Where do angioblastic cords appear?
Cariogenic mesoderm
What do angioblastic cords canalize to form?
Heart tubes
What is formed when the tubular heart joins blood vessels in other areas?
Primordial cardiovascular system
What is the pericardium derived from?
Intra-embryonic coelm
What are the parietal and fibrous layers of the pericardium formed from?
Somatic mesoderm
What is the visceral layer of serous pericardium derived from?
Splanchnic mesoderm
What are the structures on the primitive heart tube from cranial to caudal end?
- Truncus arteriosus
- Bulbus cordis
- Ventricle
- Atrium
- Sinus venosus
What structures are found in the arterial end of the primitive heart tube?
- Truncus arteriosus
- Bulbus cordis
- Ventricle
What structures are found in the venous end of the primitive heart tube?
- Atrium
- Sinus venosus
How many horns does the sinus venosus have?
2
Right and left
Where does each horn get blood from?
- Yolk sac via vitelline vein
- Placenta via umbilical vein
- Body of the embryo via the common cardinal vein
What does the truncus arteriosus continue cranially with?
Aortic sac
What arises from the aortic sac?
Aortic arches
Where do the aortic arches terminate?
Dorsal aorta
Which way does the primitive heart tube loop?
Anti-clockwise
Which regions of the primitive heart tube grow fastest?
- Bulbus cordis
- Ventricle
What do the bulbus cordis and ventricle form?
They form a u-shape known as the bulboventricular loop
How does the heart come to face the right?
The heart tube loops to the left side
What is the most frequent positional abnormality of the heart?
Dextrocardia
What other condition is dextrocardia associated with?
Situs inversus
When does the partitioning of the primordial heart occur?
Around the 27th to 37th day of embryonic development
What does the partitioning of the primordial heart involve?
1 or 2 actively growing masses of tissue
What does endocardial cushion formation result in?
Separation of the right atrioventricular opening from the left atrioventricular opening
What does septum formation result in?
Separation of the right atrium from the left atrium and right ventricle from the left ventricle
What are many cardiac malformations associated with?
Defective formation of endocardial cushion and septum formation
What can defective endocardial cushion and septum formation result in?
- Atrial septal defect
- Ventricular septal defect
When does the partitioning of primordial atrium into left and right atria take place?
Starts towards the end of the 4th week
What develop during the portioning of the primordial atrium into left and right atria?
- Septum primum and foramen primum
- Septum secondum and foramen secundum
What is the ostium primum?
Opening between septum primum and endocardial cushion
Where is the foramen secundum formed?
At the upper end of septum primum
Where is the septum secundum formed?
On the right of the septum primum
After formation what does the septum secundum do?
It grows and overlaps the foramen secundum.
Why is the septum secundum incomplete?
Perforated by oval foramen
What is the opening in the septum primum?
Foramen secundum
What is the opening in the septum secundum?
Foramen ovale
What is the role of the oval foramen?
- Allows most of the blood to pass from the right atrium to the left atrium
- Prevents the passage of blood in the opposite direction
What normally happens to the oval foramen after birth?
- It normally closes
- Increased pulmonary blood flow and shift of pressure to the lift atrium
What happens to the septum primum after birth?
It fuses with the septum secundum
What is the oval fossa in the adult heart?
A remnant of foetal oval foramen
What does non-closure of the oval foramen result in?
Atrial septal defect
What are the 4 clinically significant types of ASD?
- Foramen secundum defect
- Endocardial cushion defect
- Sinus venosus defect
- Common atrium
Who do atrial septal defects affect more often?
Females
What is the first stage in the partitioning of the primordial ventricle?
Muscular ventricular septum forms. Opening is called intraventicular foramen
What happens in the partitioning of the primordial ventricle after the muscular ventricular septum forms?
Aorticopulmonary septum rotates and fuses with muscular ventricular septum to form membranous interventricular septum, closing interventricular foramen
What is the final stage in the partitioning of the primordial ventricle?
Growth of endocardial cushions separates atria from venticles and contributes to both atrial septation (distally) and membranous portion of the interventricular septum (proximally)
What happens during the 5th week of development?
Partitioning of bulbus cordis and truncus arteriosus
What must happen before the partitioning of the bulbus cordis and truncus arteriosus?
Active proliferation mesenchymal cells in the walls of the BC and TA
What happens during the partitioning of BC and TA?
- Bulbur ridges and truncal ridges are formed
- They undergo 180 degree spiralling resulting in the formation of aorticopulmonary septum
- This septum divides BC and TA in to aorta and pulmonary trunk
What causes the spiralling of the bulbur and truncal ridges?
Streaming of blood from the ventricles
What is the most common type of congenital heart defect?
Ventricular septal defect
Where do VSDs appear?
Can appear in any part of the septum
What is the outcome of most small VSDs?
Close spontaneously
What is the most common type of VSD?
Membranous
Who do VSDs most commonly affect?
Males
Where are early pacemakers found?
Primordial atrium and then sinus venosus
When does the SA node develop?
5th week
Where is the location of the SA in and adult?
High in the right atrium near the entrance of the SVC
What do the AV node and bundle develop from?
Cells of AV canal and sinus venosus
What is cot death/sudden infant death syndrome?
Abnormalities of conducting tissue
What is the fate of the aortic sac?
Aortic arches
What is the fate of the bulbus cordis?
- Right ventricle
- Parts of the outflow tracts
What is the fate of the primitive ventricle?
Left ventricle
What is the fate of the primitive atrium?
Parts of the right and left atria
What is the fate of the sinus venosus?
- Superior vena cava
- Right atrium
What are the factors affecting the aetiology of congenital heart disease?
- Rubella infection in pregnancy
- Maternal alcohol abuse
- Maternal drug treatment and radiation
- Genetic
- Chromosomal
What congenital heart diseases are more common in females?
- Atrial septal defect
- Patent ductus arteriosus
What type of defects can maternal alcohol abuse lead to?
Septal defects
What is a common cause of cyanotic disease in newborn infants?
Transposition of great vessels
What is transposition of great vessels associated with?
- ASD
- VSD
What does transposition of great vessels permit?
Exchange of systemic and pulmonary circulation
What are the 2 causes of transposition of great vessels?
- Failure of aorticopulmonary septum to take a spiral course
- Defective migration of neural crest cells
What are the 4 cardiac defects that make up the teratology of fallot?
- Pulmonary stenosis
- Ventricular septal defect
- Dextroposition of aorta
- Right ventricular hypertrophy
What is the cause of fallot?
Unequal division of the conus due to anterior displacement of aorticopulmonary septum