Development of the heart and blood vessels Flashcards
what are the 5 stages of heart developments?
- Formation of the 4-chambered heart tube
- Cardiac Looping
- Division of the AV canal into left and right channels
- Formation of the atrial septa
- Formation of the conotruncal cushions and division of the outflow tract
List the 5 stages of heart developments, but this time write in the defect associated with each stage:
- Formation of the 4-chambered heart tube
- Situs inversus - Cardiac Looping
- Dextrocardia - Division of the AV canal into left and right channels
- Ventricular septal defects - Formation of the atrial septa
- Atrial septal defect- foramen ovale - Formation of the conotruncal cushions and division of the outflow tract
- Tetralogy of Fallot
human embryo development
how many pronuclei does the fertilised egg have?
The fertilised egg has 2 pronuclei ( from the egg and 1 from the sperm)- this is the first sign of fertilisation
what is the developing embryo like after 3 days?
-contains 6-8 cells which are all identical and pluripotent (capable of becoming every type of cell)
what is the embryo like after 5 days?
- it’s now called a blastocyst, has about 100 cells
- 2 differentiated types of cells present
- inner cell mass creates all the tissues in the body, called totipotent (embryonic stem cells)
- trophoblasts are on the outside of the embryo. they differentiate to form the placenta
at day 10, the inner cell mass further differentiates to what 2 things?
inner cell mass further differentiates to ectoderm and endoderm
(day 10) what is in between the ectoderm and endoderm and how does it form?
In between these 2 layers of differentiated cells there is another cell type that forms due to cells migrating down in between the 2 layers (will later become the mesoderm layer at day 16)
what else happens at day 10?
- there is fluid filled space and another sac opening which becomes amnion
- yolk sac ends up being part of the gut and becomes amniotic fluid surrounding the embryo
at day 16 what layers are present?
The endoderm and ectoderm like before, and between them there is now a mesoderm layer
what does the ectoderm give rise to?
Skin (epidermis)
Brain
spinal cord (CNS)
sensory organs
what does the mesoderm give rise to?
Heart Skeletal muscle Kidneys Urogenital tissue Connective tissue
what does the endoderm give rise to?
Lining of the gastro-intestinal tract
Lining of the lungs
Pancreas
Liver
what is the term given to what occurs at 18 days?
Gastrulation
when looking at the embryo at 18 days what 3 features can be seen?
1.
2.
3.
what marks the start of gastrulation at 18 days?
the primitive streak
when looking at the embryo at 18 days what 3 features can be seen?
- A ring of blood islands
- A crease called the primitive streak
- Notochord
what are blood islands (18 days)?
gaps between the endoderm and mesoderm
explain the role of the primitive streak (18 days)?
the primitive streak determines the LHS/RHS and affects the symmetry of the embryo
(establishes bilateral symmetry)
describe the appearance of the notochord and its function:
- a cartilage chord that will form part of the backbone
- gives stability to the early embryo before vertebrae formation
- the source of signalling molecules, gives the early embryo some concept of having a dorsal and a ventral surface (L and R), because different signalling molecules are released in different directions
explain the stages of the 4 chambered heart tube (step 1):
18 days
Heart develops from the primitive streak via the blood islands in the splanchic mesoderm
20 days
The blood islands slowly form together into 2 tubes called cardiogenic cords
21 days
The 2 tubes fuse down the middle to make 1 heart tube
22 days
The tube develops further, asymmetry and branches and arterial and venous end
explain what happens at 22 days in further detail?
The tube develops further and it has an opening called the sinus venosus
The tube now has asymmetric openings, forming an arterial and a venous end which will develop into arteries and veins
Beginning of asymmetry in our body because the notochord sends different signals to the LHS and RHS - bulge on the LHS.
There are branches at the ends of the tubes, the ends attach to rudimental blood supply circulating around the embryo.
At 22 days, what are the arterial and venous ends called?
Truncus arterioles and sinus venosus, which develop into arteries and veins
As the embryo is implanting into the uterus what does it develop?
a placenta, and it gets oxygenated blood from the mother and circulating its own blood
what is the name the defect that is associated with development of the heart tube?
situs inversus
what does situs inversus happen?
it occurs as a result of the notochord sending diff signals to the left and right hand side going wrong, meaning we essentially end up back to front
explain situs inversus further
- embryo gets symmetry from it’s primitive streak wrong, so everything is a mirror image
- people with situs inversus are are perfectly heathly and there are no symptoms associated with it
- organs are anatomically the opposite way around
(it can sometimes cause problems in medical examinations so you need to let the medical staff know)
what is stage 2
cardiac looping
what happens at 22 days (stage 2, cardiac looping)
- the cells at each end of the heart proliferate, lengthening the tube.
- Because the tube is in a confined space it ends up bulging and folding in on itself so that by 24 days there is a… primitive atrium
what happens at 24 days?
- no division- the future ventricles start to grow downwards and what will become the atria start to grow upwards, grows out, becoming 2 atria
- the primitive atrium loop up above the primitive ventricle
what is the role of the looping process at 24 days?
the looping process brings the primitive areas of the heart into the proper spatial relationship for development
what occurs at 35 days?
-cardiac looping continues and the ventricle folds downwards
-the 4 interior chambers are forming but are not yet divided
-the heart is beating by this stage and the foetal heart can be seen on ultrasound
the 1 tube leaving the heart becomes the aorta and pulmonary artery
at 35 days is pulmonary circulation relevant, and what is the direction of blood flow?
no, at 35 days pulmonary circulation is irrelevant
the blood goes around body, to placenta, picks oxygen and back again– so this heart is adequate to foetus
what is the defect associated with cardiac looping (stage 2)?
Dextrocardia
- This is where the loop grows the other way and goes to right side instead of the left
- All the organs are in their normal place but the heart
- Caused by chance
what is stage 3 and at what day does it start to occur?
Divisions of the AV canal, occurs at 30 days
- separation of atria and ventricles
- separation of atria in 2
- separation of ventricles in 2
what are endocardial cushions?
anchor points for septal formation, located where the ventricles meet the atria
during stage 3, what do the posterior and anterior endocardial cushions do?
the posterior and anterior endocardial cushions fuse, dividing the atria from the ventricles
explain why the atria start to divide at 30 days?
- the atria start to divide due to the development of the septum primum, which starts to grow down
- this septum has a hole in it called the foramen primum
what is the role of the foramen primum- why is it necessary to have it?
Formation of atrial septum is stage 4
It allows blood to go from RHS LHS of the heart when atria contract.
Normally, the blood from the RHS would go to the lungs and enter the LHS when it returns. But, in the embryo, the lungs are not being used so you want to bypass them because blood still needs to go from left to right somehow
does the foreman primum close, and what opens? (40 days)
yes, the foramen primum closes, and another hole opens called the foramen secundum
what starts to grow over the foramen secundum? (40 days)
Septum secundum starts to grow over the foramen secundum
what’s the difference between the septum premium and septum secundum? (40 days)
the septum secundum is more muscular and robust
at 43 days, what is happening?
- Have septum primum and secundum
- Original foramen secundum partially obscured by septum secundum-now the hole is called foramen ovale
- . Anterior and posterior endocardial cushions have fused leaving L and R atrio-ventricular canals
what does the foramen oval permit?
permits the right to left shunt of blood because there is no pulmonary circulation, its a replacement for the foramen primum which is now closed
at 43 days, why is there no blood flowing through the lungs even though the lungs are present
pressure in them too high for any blood flow, the lungs are full of fluid
what happens to the ventricular septum at 43 days?
it grows up to fuse with the now fused endocardial cushions
explain the defect associated with stage 3:
ventricular septal defect
• occurs if the septum doesn’t grow up adequately and doesn’t make good contact with endocardial cushion
• When born, the pressure in LHS is higher and so some blood moves across-can hear turbulence
• During ventricular contraction some of the blood from the LV leaks into the RV, passes through the lungs and renters the LV via the pulmonary veins and LA
what are the 2 main effects of ventricular septal defect?
- Systemic circulation doesn’t receive all the blood being pumped by the LV, CO is reduced
- Leakage of blood into the RV elevates RV pressure and volume, causing pulmonary hypotension
- blood leaking into the RV increases the RV pressure and can cause RV wall hyperplasia (enlargement) which increases o2 demand and pulmonary pressure circulation
at birth what happens?
- the lungs start to become functional
- pulmonary vascular pressure decreases, the veins and arteries in the lungs open and the resistance to blood flow through them is less, so blood starts to flow through them. -Pressure in RA and RV is reduced as blood is flowing out of the RV going to the lungs.
after birth, when LA pressure excess RA pressure what happens?
the septum primum is forced against the septum secundum functionally closing the foramen ovale (which will form the fossa ovalis). In time the septa eventually fuse.
defect associated with stage 4?
- having a patent foramen ovale is a common septal defect present to some extent in up to 25% of adults- when there is leakage across atria (may be small)
- sometimes can hear the turbulence, “hole in the heart”
what is stage 5?
Division of outflow tract
what is division of the outflow tract?
- Formation of pulmonary artery and aorta, because at the moment there is just 1 vessel leaving the heart- this needs to be divided.
- At this stage there is no separation between the ventricles all the blood from the heart leaving though one vessel.
- Eventually this single outflow is going to be separated into the left and right sides – the pulmonary artery and the aorta. (RV- pulmonary artery, LV-aorta)
Separation of the ventricles results from the union of what?
o Conotruncal septum
o Endocardial cushions
o Ventricular septum
what does the conotruncal septum do?
grows down down the conus arteriosus (centre single tube) as a spiral shape, dividing it into 2- PA and aorta
what does the conotruncal septum meet with?
It meets with the endocardial cushions and the ventricular septum. The three of them make the final full separation of the left and right sides.
what is the defect associated with the last stage?
Tetralogy of Fallot
explain what Tetralogy of Fallot involves:
when the conotruncal septum (spiral) grows off centre, or it doesn’t attach to the endocardial cushions in the right place
so, what does Tetralogy of Fallot cause (4 things)
- Pulmonary stenosis-you essentially get a large aorta and a small pulmonary artery
- Overriding aorta
- Ventricular septal defect
- Right ventricular hypertrophy
in Tetralogy of Fallot, what is the consequence of having a small pulmonary artery?
a small pulmonary artery means:
- right ventricle has to work harder to get blood to lungs
- leads to hypertrophy of the right ventricle
explain what “over-riding aorta” means in tetralogy of fallot and its consequence
over-riding aorta means the aortic opening is positioned over a ventricular septal defect allowing blood from both sides of the heat to enter the aorta
the consequence is that some deoxygenated blood is therefore pumped around the body
explain what “ventricular septal defect” means in tetralogy of fallot and its consequence
- volume overload in LV
- increase in pressure in pulmonary circulation
- occurs during systole, when blood from the LV enters the RV, passes through the lungs. the pulmonary veins and the LA, where it where it re-enters the LV
what close at birth?
what happens when the baby takes its first breath?
- lungs expand
- pressure decreases and blood enters lungs for the first time
- foramen ovale and ductus arteriosus both close.
what is the ductus arteriosus?
- a blood vessel connecting the man pulmonary artery to the proximal descending aorta
- allows most the blood from the RV to bypass the foetal fluid-filled non functioning lungs
when the ductus arteriosus closes at birth, what does it become?
ligamentum arteriosum
what does the foramen ovale become when it closes at birth?
fossa ovalis
