block III: Fetal & neonatal circulation (conf 3) Flashcards
What is an important aspect of prenatal lungs?
do not provide gas exchange and the pulmonary vessels are vasoconstricted
Which side is the high pressure and low pressure in fetus, and why?
Right side (High Pressure) bc receives blood from placenta and its not going into the lungs, it goes into the left side, Left side (Low Pressure)
what is the function of ductus arteriosus in the fetal circulation?
bypasses blood from right ventricle into aorta, instead of lungs, and rest of systemic circulation
how is the alveoli in the fetus?
full of water, lack of oxygen; pulmonary arteries are constricted due to lack of oxygen`
where does blood in the ventricle comes from?
vena cava
What are the structures important in transitional circulation?
- Ductus venosus
- Oval foramen
- Ductus arteriosus
explain the fetal circulation
- O2-rich blood returns from the placenta in the umbilical vein.
- On approaching the liver, about half of the blood passes directly into the ductus
venosus (connects the umbilical vein to the IVC). This blood bypasses the liver (emphasis on nutrition to the head). - The other half of the blood in the umbilical vein flows into the sinusoids of the liver and enters the IVC through the hepatic veins.
- After entering the IVC, the blood then enters the right atrium of the heart
- Most blood from the IVC is directed through the oval foramen into the left atrium.
- From the left atrium, the blood passes to the left ventricle and leaves though the ascending aorta
- Little blood goes to the lungs, as residual blood from right ventricle -> pulmonary trunk -> ends up passing through the ductus arteriosus (DA) -> into the descending aorta to the fetal body and returns to the placenta through the umbilical arteries (pulmonary blood flow is low).
- Only a small volume of blood from the ascending aorta enters the descending aorta thus the majority of the blood in the descending aorta passes into the umbilical arteries and is returned to the placenta for reoxygenation (the rest supplies the viscera and the inferior part of the body).
from where does the arteries of the heart, head, neck, and upper limbs receive O2- rich blood?
ascending aorta
from where does the liver receive 02-rich blood?
from the umbilical vein
What is the remnant of ductus venosus?
ligmentum venosum
what is the remnant of the umbilical vein?
ligamentum teres or round ligament of the liver
What is the first transformation of the transitional neonatal circulation?
- At birth – circulation of fetal blood through the placenta ceases and the infant’s lungs expand and begin to function; the 3 shunts that permitted blood to bypass the liver and lungs close and cease to function (the oval foramen, ductus arteriosus and ductus venosus); the umbilical vessels are no longer needed.
- The sphincter in the ductus venosus constricts (all blood entering the liver passes through the hepatic sinusoids) and occlusion of the placental circulation causes an immediate fall of blood pressure in the IVC and right atrium.
What is aeration of the lungs at birth associated with?
- dramatic fall in pulmonary vascular resistance.
- increase in pulmonary blood flow.
- thinning of the walls of the pulmonary arteries (caused from stretching as the lungs increase in size with the first few breaths).
What happens to the oval foramen at birth?
The oval foramen closes at birth – increased pulmonary blood flow produces higher pressure in the left atrium than in the right (oval foramen closes by pressing the valve against the septum secundum)
where does the output of the right ventricle flows into at birth?
into the pulmonary trunk.
