L12 Flashcards
what is the difference between circulation before and after birth
fetal circulation is a parallel circuit and adults is a series circuit
in the fetus you have shunt dependent circulation
what is the role of the placenta
it bring maternal and fetal circulations within close proximity but blood does not mix
this provides the baby with everything that it needs
describe what happens on the maternal side of the placenta
on the maternal side the uterine artery branches into the endometrium
what happens to the maternal blood flow once it enters the endometrium
In the endometrium there are pools of blood (sinus) which chorionic villi bath in
from there it goes back into the uterine vein and back into the circulation
what happens on the fetal side of the placenta
On the fetal side you have the umbilical arteries. These arteries have deoxygenated blood. There are 2 of them
They come into the placenta, gas exchange occurs and then the umbilical veins go to the heart
where do the umbilical veins and arteries enter and leave the placenta from
the umbilical cord
where does exchange from the maternal to fetal blood occur
chorionic villi
what does the placenta (chorionic villi) act as
the intestine (for nutrient uptake)
kidney (waste removal)
lungs (O2 uptake)
what kind of circulation does the placenta receive
high flow, low resistance
why does the placenta need high flow and low resistance
the fetus has high metabolic demands, it needs lots of O2 (as the placenta is acting as the lungs) therefore it needs high flow
what are the bypass routes in fetal circulation
the foramen ovale and the ductus arterioles
what happens to the lungs in the fetus
the lungs are non functional as extreme pulmonary vasoconstriction has occurred therefore the vessels have high resistance
hypoxic alveoli
what % of fetal blood flow goes to the lungs
10%
because the lungs are still growing therefore they have some metabolic demands
where is the foramen ovale located
It is a hole in the septal wall between the right and the left atrium. This makes a short cut by bypassing the pulmonary circuit
where is the ductus arteriosus located
after the carotid arteries branches
between pulmonary truck and the aorta
what % of CO flows through these shunts
90%
fetal bypass in the liver happens via what
ductus venosus
what is ductus venosus
This is involved in bypassing the liver and some of the other abdominal organs
Blood that is coming from the placenta and through the umbilical vein goes through this bypass and into the inferior vena cava
Therefore you have are getting oxygenated blood getting delivered to the fetal right atria
what % of blood uses the ductus venosus as a bypass
50-60%
the the fetus what organs need the most O2
the brain and the heart
what is the difference between fetal O2 levels compeered to an adult
in the fetus it is about 8% whereas in an adult it is 98-100%
where are the O2 demains in the fetus the highest
in the upper regions
there are 2 laminar streams in the inferior vena cava. why?
because you need to keep the deoxygenated and oxygenated blood separate otherwise you would further decrease the oxygen saturation levels
how do we ensure that the brain and the heart receive the most oxygenated blood
thorough the eustachian valve (EV)
what is the role of the eustachian valve
designed so that the IVC (oxygenated blood) get directed through the foramen ovale (directly from the right atria to the left atria) so that the oxygenated blood can go up to the upper body to the brain
The deoxygenated blood goes into the pulmonary arteries and then through the ductus arteriosus which enters the carotid body AFTER the oxygenated blood has come back down from the brain
where are what is the EV
it is a tissue flap that is located at the junction of the IVC and the RA
when does the circulatory system switch from fetal to adult
at the babies first cry
what processes cause the switch from fetal to adult circulation
when you cut the cord you get an increase in CO2
this increase in CO2 is a strong driving force for you to inhale
what causes the drop in pulmonary pressure after the first breath
When we are born we take the first breath and there is air in the alvioli so that the lungs inflate. This decreases the pulmonary resistance. The dop in resistance leads to a drop in the pulmonary pressure and resistance and increase the flow through the lungs
what causes the closure of the foramen ovale
Reduction in pulmonary pressure
decreases RA pressure
Loss of placenta which was a low resistance vessel causes an increases in Systemic vascular resistance and LA pressure
this switch in pressure greaident causes the FO to close and fiber forms around it so that it doesn’t reopen
what causes the closure of the ductus arteriosus
the placenta produces prostaglandins which keep the DA open therefore when the placenta is removed the DA closes
how long does it take for the ductus arteriosus to close
72 hours
what causes the closure of the ductus venosus
the loss of the placenta causes a decrease in umbilical sinus pressure which narrows the ductus and causes functional closure
The chorionic villous space contains all of the following substances EXCEPT:
A: oxygen
B: carbon dioxide
C: maternal blood cells
D: fetal blood
D
The pulmonary vascular resistance before birth is high
BECAUSE
oxygenated blood is shunted from the right atrium to the left atrium through the foramen ovale.
both are true but not causal
