L12

Question 1

what is the difference between circulation before and after birth

Answer 1

fetal circulation is a parallel circuit and adults is a series circuit

in the fetus you have shunt dependent circulation

Question 2

what is the role of the placenta

Answer 2

it bring maternal and fetal circulations within close proximity but blood does not mix

this provides the baby with everything that it needs

Question 3

describe what happens on the maternal side of the placenta

Answer 3

on the maternal side the uterine artery branches into the endometrium

Question 4

what happens to the maternal blood flow once it enters the endometrium

Answer 4

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

Question 5

what happens on the fetal side of the placenta

Answer 5

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

Question 6

where do the umbilical veins and arteries enter and leave the placenta from

Answer 6

the umbilical cord

Question 7

where does exchange from the maternal to fetal blood occur

Answer 7

chorionic villi

Question 8

what does the placenta (chorionic villi) act as

Answer 8

the intestine (for nutrient uptake)

kidney (waste removal)

lungs (O2 uptake)

Question 9

what kind of circulation does the placenta receive

Answer 9

high flow, low resistance

Question 10

why does the placenta need high flow and low resistance

Answer 10

the fetus has high metabolic demands, it needs lots of O2 (as the placenta is acting as the lungs) therefore it needs high flow

Question 11

what are the bypass routes in fetal circulation

Answer 11

the foramen ovale and the ductus arterioles

Question 12

what happens to the lungs in the fetus

Answer 12

the lungs are non functional as extreme pulmonary vasoconstriction has occurred therefore the vessels have high resistance

hypoxic alveoli

Question 13

what % of fetal blood flow goes to the lungs

Answer 13

10%

because the lungs are still growing therefore they have some metabolic demands

Question 14

where is the foramen ovale located

Answer 14

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

Question 15

where is the ductus arteriosus located

Answer 15

after the carotid arteries branches

between pulmonary truck and the aorta

Question 16

what % of CO flows through these shunts

Answer 16

90%

Question 17

fetal bypass in the liver happens via what

Answer 17

ductus venosus

Question 18

what is ductus venosus

Answer 18

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

Question 19

what % of blood uses the ductus venosus as a bypass

Answer 19

50-60%

Question 20

the the fetus what organs need the most O2

Answer 20

the brain and the heart

Question 21

what is the difference between fetal O2 levels compeered to an adult

Answer 21

in the fetus it is about 8% whereas in an adult it is 98-100%

Question 22

where are the O2 demains in the fetus the highest

Answer 22

in the upper regions

Question 23

there are 2 laminar streams in the inferior vena cava. why?

Answer 23

because you need to keep the deoxygenated and oxygenated blood separate otherwise you would further decrease the oxygen saturation levels

Question 24

how do we ensure that the brain and the heart receive the most oxygenated blood

Answer 24

thorough the eustachian valve (EV)

Question 25

what is the role of the eustachian valve

Answer 25

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

Question 26

where are what is the EV

Answer 26

it is a tissue flap that is located at the junction of the IVC and the RA

Question 27

when does the circulatory system switch from fetal to adult

Answer 27

at the babies first cry

Question 28

what processes cause the switch from fetal to adult circulation

Answer 28

when you cut the cord you get an increase in CO2

this increase in CO2 is a strong driving force for you to inhale

Question 29

what causes the drop in pulmonary pressure after the first breath

Answer 29

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

Question 30

what causes the closure of the foramen ovale

Answer 30

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

Question 31

what causes the closure of the ductus arteriosus

Answer 31

the placenta produces prostaglandins which keep the DA open therefore when the placenta is removed the DA closes

Question 32

how long does it take for the ductus arteriosus to close

Answer 32

72 hours

Question 33

what causes the closure of the ductus venosus

Answer 33

the loss of the placenta causes a decrease in umbilical sinus pressure which narrows the ductus and causes functional closure

Question 34

The chorionic villous space contains all of the following substances EXCEPT:

A: oxygen

B: carbon dioxide

C: maternal blood cells

D: fetal blood

Answer 34

D

Question 35

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.

Answer 35

both are true but not causal