Lecture 12 Flashcards
Describe the adult circulation
It is a circulatory system in series so there is blood from the right atrium going through the pulmonary circulation through the lungs, back to the left side of the heart and then out into the systemic circulation, going around into the tissues and then back to the right side of the heart
Describe the foetal circulation
You have the placenta which is your nutrient supply, your lungs, and so that is an additional part of the circulatory network in the foetus.
Your lungs are also not functional because you are in a liquid environment so you don’t need circulation to the lungs.
But then when you are born, you have to be able to switch to using it.
This occurs through a series of shunts through the circulatory system that can redirect flow where it needs to go
There are two different sides of the placenta. What are these called?
the maternal side and the foetal side
What is located on the maternal side of the placenta?
There is the uterine artery which branches into the endometrium
What does the uterine artery deliver?
oxygenated blood to the uterus
What is inside the endometrium?
There is pools of maternal blood with leaky capillaries and then it goes from there into the uterine veins back into the maternal circulation
What is located on the foetal side of the placenta?
There are two umbilical arteries that are coming from the foetus towards the mother.
Are umbilical arteries carrying oxygenated or deoxygenated blood?
It is deoxygenated
Where is the deoxygenated blood heading in the umbilical arteries?
towards the placenta to get ride of CO2 and to pick up O2
Where is the umbilical vein located? Where does it travel? What sort of blood does it carry?
This is inside the placenta, traveling back to the foetal part now with oxygenated blood
What forms into the umbilical cord?
the umbilical arteries and the umbilical veins
Where does the umbilical cord travel?
from the placenta to the foetus
The placenta brings the foetal circulation and the maternal circulation in close proximity. Do they mix?
no
If maternal and foetal blood don’t mix, how does gas exchange occur?
There are chorionic villi which form in a dense network that sits in the pool of maternal blood. This is where the exchange occurs (bathing in maternal blood) but there is a barrier between the two types of blood
What does the chorionic villi act as?
- the intestines (so the baby can get nutrients)
- the kidney (removing waste products)
- as the lungs (removal of CO2 and uptake of O2)
Does the placenta have a high blood flow? Why?
yes because it is acting as the lungs for the foetus
Does the placenta on the foetal side have high or low resistance? Why?
very low resistance to allow a lot of foetal blood to be able to pass through the placenta without restriction
In utero, we have lungs that are ____________ because the __________ are collapsed because we are not in an _______ environment
non-functional
airways
air
Because there is no movement of gas in the lungs in utero, we can say that there is ________ _______ so the pulmonary lungs respond by ________
utero hypoxia
vasoconstriction
Vasoconstriction in the pulmonary lungs in utero increases the _________ to flow and therefore there is increased ________ in the pulmonary vasculature
resistance
pressure
Are we sending blood through the lungs in utero? Why or why not?
no because there is no oxygenation going to be occurring
The pulmonary blood flow in the uterus makes up what percentage of cardiac output?
10%
The physiology of the hypoxic vasoconstriction allows the lungs and the pulmonary circulation to be _________-
bipassed
What are the two routes that bypass the lungs?
- foramen ovale
- ductus arteriosus
What is the foramen ovale bypass?
It is a hole in the septal wall between the left and right atrium.
What is the advantage of the foramen ovale?
It means that the blood can take a shortcut from the right atria straight into the left atria, bypassing going through the pulmonary circuit
What is the ductus arteriosus bypass?
(Not all of the blood goes through the foramen ovale. Some blood does go from the right atrium into the right ventricle, ejected from the right ventricle into the pulmonary trunk). Just before the bifurcation into the left and right pulmonary artery, we have a shunt - a connection between the pulmonary artery and the aorta.
What is the purpose of the ductus arteriosus?
It allows blood that is in the pulmonary artery to bypass the rest of the pulmonary circuit and join in at the aorta
Where does the ductus arteriosus join the aorta? Why is this location important?
It joins the aorta after the bifurcations for the carotid arteries.
This is important because it joins the aorta after the blood has gone to the head
What percentage of the cardiac output goes through these shunts to avoid going to the lungs?
90%
As well as the shunts to avoid the lungs, there is another shunt in the foetal circulation. What is this called?
Ductus venosus
What does the ductus venosus allow the foetal blood to bypass?
the liver and some of the abdominal organs
O2 rich blood that is coming from the placenta via the umbilical vein enters into the foetus and is goes through which bypass? Where does it take it?
The ductus venosus - it goes straight passed the liver and into the inferior vena cava so that we are getting O2 blood being fed into the foetal right atria
What percentage of the blood bypasses the liver via the ductus venosus?
50-60%
Why is the ductus venosus important?
(Normally in the adult, we have oxygenation occurring in the lungs, in the pulmonary circulation). In the foetus, it is in the placenta, so if we went straight from the placenta through the umbilical vein straight into the digestive system/liver, because the liver is a highly metabolic organ, it would use lots of the oxygen. This means by the time we get back to the atria to pump blood through the circulation, there would be no O2 left.
What are two things that are highly metabolically demanding in a developing uterus?
- the brain
- heart
From 6-8 weeks of pregnancy, your heart starts to ________
beat
If we didn’t bypass the lungs, we would be getting ___________ blood circulating around
liver (lung)
Which is higher, O2 saturation in an adult of foetus?
in an adult (98-100% vs (80% saturation in umbilical vein)
Oxygenated blood comes through the ________ _______ which comes through the _______ _______ into the _______ __________ _______
umbilical vein
ductus venosus
inferior vena cava
There is some perfusion in the liver, and deoxygenated blood from the liver joins the what?
the interior vena cava
How does the structure of the vena cava allow for two independent streams of oxygenated and deoxygenates blood?
Instead of one coming into merge, deoxygenated blood from the liver (portal vein) and oxygenated blood from the umbilical vein via the ductus venosus, there are two lanes of traffic heading up the inferior vena cava. We get to the right atrium and go through.
There is a higher metabolic demand in the upper/lower body of the foetus?
upper
If we didn’t have separation of blood in the inferior vena cava, we would get reduction in our __________.
oxygenation
We have blood coming from our upper body which is _______ metabolically active so there is _______ oxygen __________. Both the superior and inferior vena cava enter into the right atrium so if we had mixing of the inferior vena cava (oxygenated) and superior vena cava (deoxygenated), what would be the consequence?
this would lead to a mixed venous blood, reduced oxygen saturation
At the junction of the inferior vena cava and the right atrium, we have a valve called the what?
Eustachian valve
What is the purpose of the Eustachian valve?
It directs blood coming from the oxygenated blood in the inferior vena cava through the foramen ovale, into the left atrium, left ventricle and into the aorta
It also directs blood from the superior vena cava into the right atrium, right ventricle until it goes into the pulmonary artery, pulmonary trunk and then through the ductus arteriosus which joins after the bifurcation of the aorta
What is the advantage of the ductus arteriosus joining the aorta after the bifurcation?
Deoxygenated blood comes from the right atrium, right ventricle, into the pulmonary artery and then through the ductus arteriosus carrying less oxygenated blood. By binding after the bifurcation, we can ensure that it is mostly oxygenated blood going to the upper body and the less oxygenated blood can go to the rest of the body
Describe the flow of blood in a foetus
Blood comes from the foetus via the umbilical artery (deoxygenated blood) and goes to the placenta then towards the foetus in the umbilical veins (oxygenated). The majority of this goes through the ductus venosus into the inferior vena cava, into the right atrium through the foramen ovale and into the left atrium, into the left ventricle, into the aorta and then into the upper body. The blood coming back from the upper body comes in through the superior vena cava into the right atria, right ventricle but it goes through the ductus arteriosus, bypassing the pulmonary circulation into the descending aorta. This allows perfusion of the lower body coming back up through the inferior vena cava
When you are born, you lose the _______ support system
placental
When you are born, you have to be able to immediately switch to an __________ circulatory system
adult
When you are born, the lungs have to work straight away. True or false?
true
What is the significance of the baby’s first cry?
It helps inflate the lungs and it stimulates the switch from the foetal circulation to the adult circulation
How does the switch from foetal circulation to adult circulation come about?
You are born and you are switched from a liquid environment to an air environment. Cutting the umbilical cord breaks the connection to the placenta so now you have no way of oxygenating the foetal blood. Metabolism is still going on even without a supply of O2 which increases the CO2 levels. Increasing the CO2 levels is the big driver to taking your first breath
What is important in stimulating and switching the circulation?
It is the changes in pressure that are important in stimulating and switching the circulation
When we are in utero, we have a _______ pulmonary vascular resistance, a ________ pulmonary blood flow and a ______ pulmonary artery pressure
high
low
high
When we are born, we take our first breath, inflate the lungs and now they have air in them. There is oxygen in the alveoli so now we don’t have the stimulus for ___________ so we don’t have hypoxic ______ because we have oxygenation. The pulmonary vasculature can ________, reducing the pulmonary vasculature _________ so there is a dramatic drop in pulmonary _________ following birth
hypoxia vasoconstriction dilate resistance resistance
After birth, there is 100% of the CO going through the pulmonary vasculature. The drop in the resistance leads to a drop in the what?
pulmonary artery pressure
How does the foramen ovale close?
We have a reduction in the pulmonary pressure which reduces the right atrial pressure. There is also the loss of the placenta (which was a low resistance circulation). Losing the low resistance circulation increases the systemic vascular resistance which increases the pressure in the left atria. This has switched the pressure gradient between the two atria and closes the FO.
How does the Ductus arteriosus close?
The placenta generates a lot of prostaglandins so when you are disconnected from your placenta, you lose those prostaglandins, which are normally responsible for keeping the ductus arteriosus open. This means when we lose the placenta, the ductus arteriosus closes (within 72 hours after birth)
How does the ductus venosus close?
Because we have lost the _________, we have lost the connection to the _________ __________. This means there is a reduction in the pressure in the ____________ around the __________ which causes changes in the __________ so the ductus venosus closes
Because we have lost the placenta, we have lost the connection to the umbilical veins. This means there is a reduction in the pressure in the sinuses around the liver which causes changes in the pressure so the ductus venosus closes
The chorionic villous space contains all of the following substances EXCEPT: A: oxygen B: carbon dioxide C: maternal blood cells D: foetal 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 true but unrelated
