Embryology of the cardiovascular system Flashcards
Which 2 ways can blood vessels form?
vasculogenesis - blood vessels arise from assembly of angioblasts to form blood islands
angiogenesis - sprouting of new vessels from existing ones
Describe primitive circulation
heart beating by 22 days
blood enters the heart via 3 main veins into the sinus venosus (cardinal veins, vitelline veins, umbilical vein)
atria, ventricles, bulbus cordis (conus cordis) and truncus arteriosus
leaves aortic sac via aortic arches, enters brachial arches to the dorsal aortae
When does septation occur?
mid 4th week to the end of 5th week the heart tube undergoes partitioning into 4 chambers
Describe the process of septation
atrioventricular partitioning
atrial partitioning
ventricular partitioning
Describe atrial partitioning
successive partitioned:
- septum primum
- septum secundum
divides primitive atrium into 2 chambers (right atrium + left atrium)
Describe the septum primum and how atrial partitioning occurs
sickle shaped crest, grows down to form the roof of the common atrium
fuses with endocardial cushions - before fusion forms the foramen primum
foramen primum obliterated
cell death superiorly forming foramen secundum
Describe ventricular partitioning
primitive ventricle is divided into 2 chambers: right ventricle and left ventricle
interventricular septum - muscular crescentic growth up from floor of primitive ventricle to fuse with endocardial cushions
When does the interventricular foramen close?
end of 7th week
What state are the pulmonary vessels in prenatally?
lungs do not provide gas exchange, pulmonary vessels are vasoconstricted
Describe fetal circulation
approx half of blood bypasses liver via ductus venosus to pass to the IVC
other half flows to the sinusoids of the liver and enters the IVC via hepatic veins
blood in IVC mixes with poorly oxygenated blood from the lower limbs, abdomen and pelvis then flow into the right atrium
blood entering the right atrium still has high oxygen content - blood entering atrium gets diverted to flow through the foramen ovale to pass into the left atrium
in left atrium the blood mixes with poorly oxygenated blood from lungs
blood then passes to left ventricle and out of the ascending aorta to the head, neck and upper limbs
remaining highly oxygenated blood in right atrium mixes with poorly oxygenated blood from SVC and passes to right ventricle
medium oxygen content blood will flow to pulmonary trunk
some will go to lungs and rest through ductus arteriosus (between pulmonary trunk and aorta) and then pass to descending aorta
65% of this blood will return to placenta via umbilical arteries
remainder will supply viscera and lower body
What 3 shunts are present in fetal circulation?
ductus venosus
foramen ovale
ductus arteriosus
What does aeration of the lungs at birth cause?
dramatic decrease in pulmonary vascular resistance
marked increase in pulmonary blood flow to the lungs
progressive thinning of the walls of the pulmonary arteries
oxygenated blood from the lungs flows into the left atrium
What causes the foramen ovale to close?
blood in the right ventricle flows to the pulmonary trunk and due to the pulmonary vascular resistance now being lower than the systemic vascular resistance the ductus arteriosus reverses - blood flows from the descending aorta to the pulmonary trunk
results in pressure in the left atrium becoming higher than in the right atrium - this closes the foramen ovale
When does the ductus arteriosus close?
constricts at birth
fully close between 48-96hrs post birth
When does the left ventricle become thicker than the right?
fetal circulation = right ventricle thicker
by 5th month the left ventricular wall becomes thicker
