Development of the heart Flashcards
Outline the five steps involved in the development of the heart
1) Formation of the 4 chambered heart tube
2) Cardiac looping
3) Division of atrioventricular canal into left and right channels
4) Formation of the atrial septa
5) Formation of the conotruncal cushions and division of the outflow heart
What is the morula?
Solid ball of cells formed as the zygote undergoes cleavage
What is a blastocyst?
A hollow ball of cells with a fluid filled cavity
What is a Gastrula?
An embryo with three primary germ layers(ectoderm, mesoderm and endoderm)
What does the ring of blood island towards?
Ring of blood islands towards the head in a horse shoe shape
What does the primitive streak define?
Primitive streak define the left and right of the embryo
What will the notochord form?
Notochord will form part of the backbone
What do the blood islands start to do and form what?
Blood islands start to fuse together and form two kinds of basic tubes
What are these basic tubes called?
These are called the cardiogenic chords
What do these cardiogenic chords do?
Cardiogenic chords fuse down the middle to make one single tube
What is there at the end of these tubes and what do these ends do?
There’s a little bit of branching at the end of the tubes and these ends attach to the rudimentary blood supply that is starting to circulate around the embryo
What happens after 18 days in terms of the formation of the heart tube?
-Heart develops from the primitive streak via the blood islands in the splanchnic mesoderm
What happens after 20 days in terms of the formation of the heart tube?
Blood islands slowly form together into 2 tubes called cardiogenic cords
What happens after 21 days in terms of the formation of the heart tube?
The tube fuse down the middle to make one heart tube
What happens after 22 days in terms of the formation of the heart tube?
Further development gives rise to a tube with asymmetric openings forming an arterial and venous end
The beginning of asymmetry in the bulge to the left
What is situs inversus?
Some people are a complete mirror image
Asymmetry is defined and location is defined by the primitive streak
They’re perfectly healthy
What is the cardiac looping like after 22 days?
Cells at each end of the heart proliferate making the tube longer
Entire structure is in a confined space so begins to fold up on itself
What is the cardiac looping after 23 and 24 days?
The primitive atrium loops up above and behind the primitive ventricle
Looping process brings the primitive areas of the heart into the proper spatial relationship for development
What is dextrochardia and whats it caused by?
All the organs are in the normal place apart from the heart which is on the right side
Caused by chance
What is the cardiac looping after 24 days?
Primitive atrium we see from the front when viewed from the side is growing out of the back and become two atria
What is the cardiac looping after 35 days?
Heart is beating by this stage and the foetal heart can be seen on an ultrasound
However the four interior chambers are not yet divided
How many years after does the atrioventricular canal divide?
30 days after
What is the septum primum?
Grows along the midsagittal plane separating the atria except for a temporary space called the foramen primum
What does the left side of the atrium grow during the division of the atrioventricular canal?
Left side of the atrium grows pulmonary veins sending growing veins to the developing lungs
What fuse together to divide the atria from the ventricles?
The posterior and anterior endocardial cushions fuse, dividing atria from the ventricles
What will the ventricular septum eventually do?
Ventricular septum will eventually grow upwards to form a division between the two ventricles
-It will attach to the divisions between atria and ventricles
What is once cause of ventricular septal defect?
It is the failure of the endocardial cushions to provide an anchor point for the developing ventricular septum
What happens during ventricular contraction in a ventricular septal defect?
During ventricular contraction, some of the blood from the LV leaks into the RV
What are the 2 main effects in ventricular septal defect?
1) Systemic circulation doesn’t receive all the blood being pumped by the left ventricle
2) Leakage of blood into the right ventricle elevates right ventricular pressure and volume, causing pulmonary hypertension
When is the atrial septa formed?
40 days
