Embryology Flashcards
What are the two tubes that eventually fuse to form the heart?
Cardiogenic tubes
What is it called when these two tubes fuse together?
Primitive heart tube - this is stage 1
What is stage 2 in heart development?
Heart looping
What is stage 3 in heart development?
Atrial and ventricular septation
What is stage 4 in heart development?
Outflow tract septation
What germ layer gives rise to the heart?
Lateral plate splanchnic mesoderm
What is the earliest system to form and begin functioning within the developing human and why?
Cardiovascular system - starts to function at the beginning of the 4th week (22nd day), circulatory system is essential to carry nutrients + waste around the rapidly growing embryo to keep its cells alive - nutrition by diffusion is not enough to satisfy the growing embryo
What does the developing heart invaginate into?
Pericardium
What is the process to form the primitive heart tube?
Angiogenic cell islands (blood islands) form in the lateral plate splanchnic mesoderm and coalesce into 2 tubes (day 18) and then move towards the midline and fuse to form the primitive heart tube (day 22)
When it fuses together to form the primitive heart tube - why can we call it the heart?
Because it has striating pumping - blood is moving up through the tube
What germ layer is the parietal layer of serous pericardium and fibrous pericardium formed from?
Somatic mesoderm
What germ layer is the visceral layer of the serous pericardium formed from?
Splanchnic mesoderm
What end is blood coming into the heart tube?
Caudal end (venous)
What end is blood coming out the heart tube?
Cranial end (arterial) - towards the head
What are the 5 sections of the primitive heart tube?
Truncus arteriosus Bulbus cordis Ventricle (primitive) Atrium (primitive) Sinus venous (right and left horns)
What day does the tube starting folding?
Day 23
Which way does it fold down to?
Down to the right
What does the truncus arteriosus continue cranially to become?
Aortic sac
What is the definition of a vein?
Vessel that takes blood back to the heart
Where does gas exchange take place in the foetus?
Adults have gas exchanging lungs to oxygenate their blood, whereas foetus’ do not, instead they have a placenta which oxygenates their blood and removes carbon dioxide (note that there is no mixing of blood - nutrients diffuse across)
How is oxygenated blood carried from the placenta to the foetus?
Umbilical vein
What is dextrocardia?
Where the heart loops the wrong way - loops to left side (instead of right)
By what day is the tube folded into a heart-like shape?
Day 28
What is the blood flow by day 28?
Blood flows in the caudal end through the sinus venosus, into a common atrium -> atrioventricular canal -> primitive LV -> interventricular foramen -> primitive RV -> bulbus cordis (conus cordis and truncus arteriosus
At this stage the heart has 2 primitive chambers connected by a common atrioventricular canal - what do we need to do now?
During week 4 endocardial cushions develop to partition the atria and ventricles -> left AV canal and right AV canal
What divides the AV canal into left and right?
Fused endocardial cushions
What do we need to separate the heart into 2 atria and 2 ventricles?
2 septa develop
What clinical significance does the endocardial cushion formation and septum formation have?
ASD and VSD
What is happening at the same time as the endocardial cushions?
A spiral septum is forming in the outflow tract
What is happening at the same time that the atrial septum is forming?
The ventricular septum is forming
What is the process of the ventricular septum forming?
A muscular septum grows up to from the IV septum - separating the ventricle into left and right (endocardial cushions also grow in from the sides (between atria and ventricles)
What is the final part of the IV septum?
The membranous part - it develops from a different source
What is happening when the atrioventricular canal is dividing?
A spiral septum is forming in the outflow tract (conotruncal ridges)
What contributes to the membranous part of the interventricular septum?
The spiral septum forming in the outflow tract (conotruncal ridges)
What is a good way to understand the twisting?
Look at a diagram of the fully formed heart
During what week of life does the partitioning of the bulbus cordis and the truncus arteriosus take place?
Week 5 (starting day 29)
The pulmonary trunk and aorta are derived from which primitive heart structure?
Truncus arteriosus - eventually divides and gives rise to the ascending aorta and pulmonary trunk
What does the bulbs cordis form?
Right ventricle
?parts of the outflow tract?
What does the primitive ventricle form?
Left ventricle
What does the primitive atrium become?
Anterior portions of both the right and left atria and the two auricles
What does the sinus venous develop into?
Posterior portion of the right atrium, the SA node and the coronary sinus
(? superior vena cava?)
How many shunts develop to bypass the pulmonary circulation?
2
What happens to them both after birth?
They close up
What does the foramen ovale leave?
Fossa ovalis
What chamber is not used in the foetal heart?
Right ventricle
What is the function of the ductus arteriosus in the foetus?
Blood which passes into the pulmonary circulation is redirected into the systemic circulation by the ductus arteriosus
What is the ductus arteriosus?
A blood vessel connecting the main pulmonary artery to the proximal descending aorta
What does the ductus arteriosus become?
Ligamentum arteriosum
What is the ductus venosus?
A vessel which shunts the blood of the umbilical vein directly to the IVC - allows oxygenated blood from the placenta to bypass the liver (so its a vessel that connects the umbilical vein to the IVC)
In the foetus, oxygenated blood from the placenta first enters the ___ of the heart
Right atrium
What is the function of the foramen ovale?
Allows blood to enter the LA from the RA - allows blood to bypass the (non-functioning) lungs
What is the ligament venosum?
Fibrous remnant of the ductus venosus of fetal circulation
