Development of Heart & Vessels Flashcards
What are the stages of Heart development & the potential defects that can occur?
- Formation of 4 chambered heart (situs inversus)
- Cardiac Looping (dextrocardia)
- Division of atrioventricular canal into L & R channels
(ventricular septal defect) - Formation of atrial septa (atrial septal defect)
- Formation of conotruncal cushions &divisions of
outflow tract (Tetralogy of Fallot)
What is the first sign of fertilisation observed within the embryo?
Embryo has 2 pronuclei
Describe the development of a human embryo
Developing embryo contains 6-8 cells 3 days after fertilisation
5 days after its called a blastocyst and contains ~100 cells
What are the 3 structural divisions of a developing emrbyo?
Ectoderm
Mesoderm
Endoderm
What is the ectoderm?
skin (epidermis), brain, spinal cord, CNS, sensory organs
What does the mesoderm eventually form?
heart, skeletal muscle, kidneys, urogenital, connective tissues etc.
What is the endoderm?
lining of GI tract and Lungs, pancreas, Liver etc.
What occurs during gastrulation?
primary germ layers are formed
- (endoderm, ectoderm and mesoderm)
organised into their proper locations
When does the formation of the heart tube begin to occur?
after 18 days
Where does the heart initially begin to develop from?
The heart develops from the primitive streak via the blood islands in the Splanchnic mesoderm
Explain how the heart tube develops during the 20th - 22nd days of gastrulation
20 days
- blood islands slowly form together into 2 tubes called
cardiogenic cords
21 days
- the tubes fuse down the middle to form one heart tube
22 days
- further development gives rise to a tube with
asymmetric openings forming an arterial & venous end
- beginning of the asymmetry in bulge towards left
What is the situs inversus?
A congenital condition where major visceral organs are reversed / mirrored from their original positions
When does Cardiac looping begin to occur?
after 22 days
How does cardiac looping occur during the 22nd - 24th days?
22 days
- cells at each end of the heart proliferate making a
longer tube
- entire structure is in a confined space so folds up on
itself
23 - 24 days
- primitive atrium loops up above and behind the primitive
ventricle.
- looping process brings the primitive area of the heart
into the proper spatial relationship for development
At 35 days
atria and ventricles in correct positions and tubes for circulation are ready
What is dextrocardia?
rare congenital heart condition where the heart points to the right side of the chest rather than the left as normal
What is the role of the septum primum?
Division of the atrioventricular canal
Septum primum grows along the midsagittal plane, separating the atria for a temporary space called the Foramen Primum
How does the division of the atrioventricular canal occur?
The posterior & anterior endocardial tissues fuse, dividing the atria from the ventricles
The left side of the atrium grows pulmonary veins sending growing veins to the lungs
A ventricular septum eventually grows upwards, forming a division between the 2 ventricles. - attaches to atrial and ventricular division
What is the consequence of ventricular septal defect?
During ventricular contraction, some blood form left ventricle leaks into right ventricle, passing through lungs and re enters the left ventricle via the pulmonary veins and left atrium.
Approximately how big is the ventricular septal defect?
the extent of the opening can vary from pin size to complete absence of the ventricular septum
- viewed via ECG (mid-oesophegal 4 chamber view)
What are the 2 main effects of the ventricular septum defect?
- systemic circulation doesn’t receive all the blood being
pumped out the left ventricle - leakage of blood into right ventricle elevates right
ventricular pressure& volume causing pulmonary
hypertension
What can cause ventricular septum defect?
one cause is the failure of the endocardial cushions to provide an anchor point for the developing ventricular septum
What occurs during after 40 days of gastrulation?
Formation of the atrial septa
What is the first step of the atrial septum formation?
initially the temporary hole in the septum primum (foramen primum) allows right to left shunt for foetal blood as there’s no pulmonary circulation.
this closes before a second hole, foramen secundum opens
What occurs at 40 days of heart development?
a second more muscular and robust septum grows down from the roof of the atria just lateral to the septum primum.
it obscures the place the foramen primum was