Development of the Heart Flashcards
What is vasculogenesis?
Making a blood vessel from scratch
What is involved in vasculogenesis?
Differentiation of precursor cells into endothelial cells and the de novo formation of a primitive vascular network
What is angiogenesis?
The growth of new capillaries from pre-existing blood vessels
In which week of development does formation of the heart begin?
When is the first contraction of the heart?
week 3
The first contraction occurs on day 22
The heart starts to beat as soon as it develops
In how many live births do congenital heart defects occur?
5-8 in 1,000 live births
What are the three concentric layers of the heart?
What do they develop from?
- Epicardium
- Myocardium
- Endocardium
They develop from the primary or secondary heart field
What layer of the heart is the epicardium?
What else does it form and what is it derived from?
It is the outer layer of the heart
It is also the visceral (inner) layer of the pericardium
It is derived from visceral mesoderm
What layer of the heart is the myocardium and what is it derived from?
It is the middle layer of the heart
It is derived from the visceral mesoderm overlying the heart tube
What is the endocardium derived from?
What is different from the other layers of the heart?
It is derived from the heart tube
It is not specialised do blood cells do not stick to it
If they do, this leads to clots
What is the pericardium and what are its 2 layers?
It is the sac in which the heart sits
The outer layer is the parietal pericardium
The inner layer sits on the heart and is the visceral pericardium (epicardium)
In the first stage of vasculogenesis, what is the role of the endoderm?
The endoderm induces some cells of the overlying splanchnic mesoderm to differentiate into angioblasts
What are angiogenic cell clusters?
On what day do they form?
Specialised cell clusters that will form primary heart fields
They form on day 17
During vasculogenesis, what do the angioblasts differentiate into?
Endothelial cells and endocardial tubes
2 endocardial tubes form on day 18
What happens to the endocardial tubes during lateral folding?
The endocardial tubes fuse to form the primitive heart tube
After the primitive heart tube has formed, what does the mesoderm do?
The visceral mesoderm surrounding the primitive heart tube differentiates to form the myocardium
This is the heart muscle outside of the tube
After the myocardium has formed, what does it secrete?
What is the function of the secretion?
It secretes a thick layer of extracellular matrix called cardiac jelly
Cardiac jelly is acellular and important in septation of the heart
What is the role of craniocaudal folding in development of the heart?
It brings the developing heart tube into the thorax
During craniocaudal folding, where are the primary heart fields derived from?
What level is this at?
Derived from the primitive streak at the cranial end
This is at the level of the oropharyngeal membrane
What is formed from the 3 layers of the heart tube?
Endocardium - internal endothelial lining
Myocardium - muscular wall
Epicardium - covers outside of heart and is responsible for formation of coronary arteries
As the heart develops, when do the associated vessels develop?
The heart develops with the associated vessels at the same time
In the caudal region of a 4 week embryo, which vessels are present?
3 paired veins drain into the tubular heart via the right and left horn of the sinus venosus
What vessels are present in the cranial region of a 4-week old embryo?
The cranial region connects to 2 dorsal aortae
What is the first part of the heart tube?
What is the inflow and outflow to this region?
Sinus venosus
Arterial outflow is at the cranial end
Venous inflow is at the caudal end
With differential growth of the heart tube, which 5 dilatations become apparent?
- truncus arteriosus
- conus arteriosus
- ventricle
- atrium
- sinus venosus
What is the role of the sinus venosus after differential growth?
It is at the caudal end and it receives blood
What do the primitive atrium and ventricle go on to form?
What is different about their position in foetal anatomy?
They predominantly form their named structure
The atria are at the caudal end but this changes during cardiac looping
What is the bulbus cordis?
How does this change with time?
It is the common outflow tract at the cranial end
It consists of the truncus arteriosus and conus arteriosus
As cells are added, it is differentiated between 2 parts
What is the conus arteriosus and truncus arteriosus?
The truncus arteriosus is the outflow tract
The conus arteriosus is the region just before blood reaches the pulmonary valves
On which day does cardiac looping begin?
What is significant about the start of this process?
Day 23
The heart starts to fold in preparation for dividing into 4 chambers
During cardiac looping, how does the bulbus cordis move?
It moves caudally, ventrally and to the right
As it is a fixed tube, other parts of the tube begin to move with it
How does the primitive ventricle move during cardiac looping?
The primitive ventricle is displaced before moving back to the midline
The ventricle starts to swing round in a C-shaped loop
Which part of the heart tube is displaced the most during cardiac looping?
The sinus venosus
It swings round the most as it starts in the caudal region and moves towards the cranial region
How does the primitive atrium move during cardiac looping?
It displaces cranially and dorsally
How is the apex of the heart formed during cardiac looping?
It is formed by the ventricles at the end of cardiac looping
By which week has the sinus venosus largely degenerated?
week 5
What does the right horn of the sinus venosus form?
The sinus venarum
This is the smooth part of the atrium
How is the sinus venarum differentiated from the majority of the right atrial wall (where is this derived from?)?
The sinus venarum is smooth
The rest of the right atrium is trabeculated and derived from the primitive atrium
What is the border between the trabeculated part of the right atrium and the sinus venarum?
Crista terminalis
From which part of the heart tube are the pectinate muscles and the rough part of the heart formed from?
Primitive atrium
What does the left horn of the sinus venosus form?
The oblique vein of the left atrium and coronary sinus
What is the ventricular wall formed from?
The majority of the ventricular wall is formed by the primitive ventricle
There is a small contribution from the conus arteriosus
What does the conus arteriosus go on to form?
The smooth walls of the right and left ventricles which lead into the aorta and the pulmonary trunk
This is the aortic vestibule and the conus arteriosus
Where is the aortic vestibule located and what is it?
It is on the left side of the heart
It is a smooth part of the ventricle just before the outflow tract (aorta)
Where is the conus arteriosus (adult) located and what is it?
It is on the right side of the heart
It is a smooth part of the ventricle just before the outflow tract (pulmonary trunk)
What part of the ventricle is formed from the primitive ventricle?
The trabeculated (rough) walls of the ventricle
This includes the muscular ridges of the trabeculae carneae
During further differentiation of the atria, how does the left atrium differ to the right atrium?
The right atrium enlarges by incorporating the right sinus horn
The left atrium undergoes remodelling
What happens to the left atrium during further differentiation of the atria?
An outgrowth of the left atrial wall forms a single pulmonary vein
This branches into left and right pulmonary veins, which bifurcate to form 4 pulmonary veins
During which week are the 4 pulmonary veins incorporated into the wall of the left atrium?
What is this process and what does it form?
during week 5
This process is intussusception and it forms a small roughened area
When does septation of the atria begin?
What is the first stage of this process?
At the end of week 4
Septation begins with the formation of the septum primum
What is the septum primum?
A crescent shaped outgrowth from the dorsal wall
What forms from the initial extension of the septum primum?
The septum primum extends and the diminishing connection between the left and right sides of the primitive atrium is the foramen primum
This is a slight hole between the atria
How are dorsal and ventral endocardial cushions formed?
The septum primum extends into the atrium
The endothelium lining the boundary between the atrium and ventricle expands to form the cushions
What other component helps to form the dorsal and ventral endocardial cushions?
cardiac jelly
What happens to the endocardial cushions after they have formed?
They fuse in the midline to form the atrioventricular septum
What has happened in septation by week 6?
What is the consequence of this?
The septum primum has fused with the atrioventricular septum
This obliterates the ostium (foramen) primum
In septation, what is the consequence of apoptosis occurring?
It occurs in the upper part of the septum primum to form the foramen secundum
What happens in septation at the same time as formation of the foramen secundum?
A crescent-shaped projection forms from the dorsal wall of the atrium
This is the septum secundum
How does the position of the septum secundum relate to the septum primum?
The septum secundum develops to the right of the septum primum
What is significant about formation of the septum secundum?
It does not form a complete partition
The opening left in the septum secundum is the foramen ovale
What is the role of the foramen ovale?
It allows blood to flow from the right atrium to the left atrium
This allows the lungs to be bypassed in foetal circulation
What happens to the septum primum and septum secundum after birth?
Pressure pushes the 2 septa together until they eventually fuse
What happens to the foramen ovale after birth?
It is closed as the 2 septa fuse together
The fossa ovalis is a slight indentation where the foramen ovale once was
What are the 2 origins of the interventricular septum?
- muscular part
2. membranous part
How does the muscular part of the interventricular septum form?
what else forms?
Which week does this occur in?
The muscular part projects from the floor of the primitive ventricle towards the endocardial cushions
This leaves an interventricular foramen
This occurs at the end of week 4
How does the membranous part of the interventricular septum form?
The membranous part projects inferiorly from the endocardial cushion
During which week does the membranous part of the septum close the interventricular foramen
during week 7
What does septation of the bulbis cordis lead to?
Formation of the aorta and the pulmonary trunk
During septation of the truncus arteriosus, what will divide the truncus arteriosus into 2 channels?
Endocardial swellings called conotruncal ridges
What happens to the conotruncal ridges (swellings) after they have formed?
They fuse to form the conotruncal septum
What happens to the conotruncal septum and what is significant about this?
The conotruncal septum fuses with the interventricular septum
This separates the outflow of the right and left ventricles
What pattern of movement is followed when the conotruncal swellings fuse together?
Why?
They do not fuse in a straight line - they spiral round each other
This allows the RV to connect with the pulmonary trunk and the LV to connect with the aorta
What is the role of neural crest cells in septation of the truncus arteriosus?
They help with the spiral formation of the conotruncal septum
Which 2 organs is blood shunted away from in foetal circulation and why?
Liver and lungs
Mother’s circulation will oxygenate and detoxify the blood
A small amount of blood goes to these organs for their development
Which vein carries oxygenated blood from the mother to the foetus?
Umbilical vein
After passing through the umbilical vein, where does the blood flow?
Some enters the liver and the rest enters the ductus venosus
Blood entering the ductus venosus bypasses the liver and enters the inferior vena cava
What is the passage followed by foetal circulation as blood enters the heart?
The inferior vena cava enters the right atrium
Most blood passes through the foramen ovale into the left atrium
It then enters the left ventricle and aorta
What is significant about blood entering the right atrium from the SVC?
What vessel does it travel in?
Blood entering the RA from the SVC is poorly oxygenated as it is returning from the lungs
It passes through the ductus arteriosus
How does the blood in the ductus arteriosus affect the blood in the aorta?
The blood in the ductus arteriosus is deoxygenated
It will reduce the oxygenation of the blood in the aorta
What is the ductus arteriosus and what is its purpose in foetal circulation?
It connects the main pulmonary artery to the proximal descending aorta
It allows blood from the RV to bypass the lungs
What happens to the ductus venosus after birth?
What does it form?
Termination of umbilical circulation causes the ductus venosus to close and degenerate
This forms the ligamentum venosum in the adult
How does the first breath affect the pulmonary arteries and atria?
It causes the pulmonary arteries to dilate and changes the pressure in the atria
What will increase the pressure in the left atrium after birth?
Blood returning from the lungs
What happens to the septum primum and septum secundum after birth?
The flimsy septum primum is pushed against the sturdy septum secundum
They fuse to close the foramen ovale
What structure does the foramen ovale form in an adult?
The fossa ovalis
How does the first breath affect the ductus venosus?
It causes changes in oxygen saturation in the ductus venosus
This causes it to constrict
What does the ductus venosus form in the adult?
Ligamentum arteriosum
