Biology 3602A/B Lecture Notes - Lecture 19: Ductus Arteriosus, Pulmonary Artery, Pulmonary Circulation

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5 Aug 2016
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*alligators/crocodiles spend a lot of time in the water, so in the air, R ventricle contracts,
L ventricle contracts, L ventricle is sending oxy’d blood out into systemic circ, and R
ventricle generates pressure, but pressure isn’t great enough to open the valve to the L
aorta
*It’s enough pressure to impel/push blood into the pulmonary artery but none of
it gets out into the aorta, so it’s just behaving like a normal mammalian heart
(deoxy’d blood going to lungs, oxy’d blood going out into circulation)
*Heart anatomy is odd: flap valve is passive – if enough P is there, it opens, if not enough
P, it’s closed
*So the R ventricle is not producing a lot of pressure b/c you don’t want to blow out your
lungs, so there’s only a little bit of pressure, so it goes to the pulmonary artery
*Another valve can close off the pulmonary artery called the cog valve
*When the crocodile dives, there is some nervous stimulation to close cog valve (it has
smooth muscles around it to do so)
*Closes down, increasing resistance
*So BP generated by R ventricle can no longer go out to the pulmonary artery; all
that pressure stays within the chamber until it’s great enough to open up the
flap valve and the blood flows out into the right aorta
*Right aorta can communicate through foramen, so some blood goes into the left
aorta
*So there’s shunting of blood from R side of the heart to the L side of circulation
*We don’t know why this happened in evolution, as it doesn’t help the crocodile dive
longer
*Mammals and birds convergently evolved their circulatory anatomy
*Complete separation of atria and ventricles
*Atria and ventricles can send blood to diff places for gas exchange (R side goes to
pulmonary artery; L side goes to systemic tissues)
*Since they’re completely separate, you can regulate pressure in these circuits
separately
*Right ventricle is not very strong; because if too strong, might blow out a lung in
the pulmonary circuit
*Complete separation: maximal chances of gas exchange and separate pressure
regulation
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*There may be times where you need to regulate where the blood is going
*We’ve talked about diving in seals and how they prioritize where the oxy’d blood goes
*You can vasoconstrict some of the blood vessels leading to organs that are useless
during a dive e.g. the pancreas
*Don't really know how it occurs in seals b/c of animal rights issues
*Could be nervous control by sympathetic nervous system
*There are developmental things that happen as well (previous slide was acute)
*Nonplacental animals include marsupials and monotremes
*In placental mammals, there is some shunting of blood that occurs while the fetus is
gestated
*Placental fetus get oxy’d blood from the mother’s bloodstream across the placenta
*Gas exchange across placenta
*Oxy’d blood returning from placenta ends up at the heart at the R atrium
*If it worked just like a regular mammal heart, it would get pumped from R atrium to R
ventricle, then to pulmonary artery, to the lungs
*But lungs are full of fluid, so why pump it there?
*Between R and L atrium, there's another hole called the foramen ovale (oval
hole)
*Thus, much of the blood that returns to the R atrium actually gets pumped into
the L atrium
*From L atrium, it goes into the L ventricle, and then into the systemic circulation
*So oxy’d blood, most of it, goes out from R atrium to L atrium, into systemic circ
where the fetus needs it
*Not ALL of the blood; some of the blood still goes to the pulmonary artery, but in the
fetus there is a connection between pulmonary artery and aorta called the ductus
arteriosus
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