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  • - You know, there's that saying

  • that it takes a village to raise a kid.

  • Well, I guess you could say that it takes an entire body,

  • and I mean every single organ of a body,

  • to make a baby.

  • It's like the best example of teamwork that there is,

  • all the organs in the body working together

  • to support the growth and the development of the fetus,

  • but also just as important, to make sure

  • that mom's body isn't sacrificing its own needs

  • to support the pregnancy.

  • So in order to accomplish that,

  • pretty much every organ system

  • undergoes a significant amount of change.

  • And I wanna go through what those changes are.

  • So let's start with the cardiovascular system,

  • so the heart and the blood vessels throughout the body.

  • And, I guess you could say, at the very basic,

  • most essential, level, the body needs more blood

  • to carry oxygen and those nutrients to the fetus.

  • So the blood volume increases by something

  • like 40 to 50 percent throughout the pregnancy.

  • And it's not just that there's more blood.

  • The heart is also working harder

  • to more efficiently supply that blood to the fetus.

  • So, for example, the heart beats more quickly.

  • It beats, like, 10 to 15 beats more

  • each minute than usual.

  • And the stroke volume, so the amount of blood

  • that's pumped out with each heartbeat, increases,

  • which means that the cardiac output,

  • or the amount of blood that's pumped

  • out of the heart each minute, also increases.

  • So in summary, more blood is being pumped out of the heart

  • to meet the demands of the fetus.

  • So if you had to take a guess,

  • what do you think happens

  • to blood pressure during pregnancy?

  • I'm gonna guess that you guys guessed that it increases,

  • because that's certainly what I thought happened.

  • But it actually decreases.

  • And it decreases for a couple of different reasons.

  • Firstly, there's a lot of progesterone

  • floating around in the blood during pregnancy.

  • And, if there's something that progesterone

  • does really well, it relaxes smooth muscle.

  • And that includes the smooth muscle

  • that surrounds all of the blood vessels.

  • So that relaxation causes

  • dilation of the blood vessels,

  • which then lowers the blood pressure.

  • So that's a first cause, sort of,

  • of the decrease in blood pressure through pregnancy.

  • The second thing that contributes

  • to the lower blood pressure is the placenta,

  • which is an addition of an entirely brand-new

  • blood vessel circuit to the circulatory system.

  • It's like when you add a resistor in parallel,

  • reducing the resistance of the entire circuit.

  • I'm just joking. That doesn't help anyone

  • understand it any better.

  • I guess you can think of it kind of,

  • kind of as a tall apartment building

  • and what would happen to the pressure in the shower heads

  • if you added a whole additional floor of apartments,

  • with shower heads that are really leaky

  • and let out a lot of water.

  • The placenta is kind of like that.

  • It's a really low-resistance circuit.

  • And also, while we're talking about

  • the cardiovascular system, there's a syndrome

  • that's called Supine, it's called Supine ..

  • "Supine" means when you're lying on your back,

  • Supine Postural, so it's Supine Postural,

  • "Postural" meaning related to posture,

  • Supine Postural Hypotensive

  • Syndrome, so Supine Postural Hypotensive Syndrome.

  • And it's weird that I'm talk about a syndrome

  • in a video that's talking about physiology during pregnancy.

  • But I guess you could say, it's a syndrome,

  • or something that goes wrong,

  • due to normal pregnancy physiology.

  • So anyways, what it refers to is when,

  • late in the course of a pregnancy,

  • the uterus becomes larger, right?

  • And when the uterus becomes larger,

  • it can compress the inferior vena cava.

  • So that kind of looks like this.

  • And since the inferior vena cava gathers the blood

  • from the veins of the lower body

  • and returns that blood to the heart,

  • the compression of the inferior vena cava

  • means that less blood is pushed back to the heart,

  • meaning that less blood is pumped out with each heartbeat.

  • And that leads to low blood pressure, or hypotension.

  • Right? So that's where the "Hypotensive"

  • in this name comes from.

  • So the woman starts to feel light headed

  • and like she's about to faint,

  • especially when she's on her back,

  • because that's the position, when she's on her back,

  • that's the position in which the uterus is exerting

  • the most pressure on the inferior vena cava.

  • A really quick way to resolve that issue

  • is for the woman to turn to her left side,

  • and that tilts the uterus to the left

  • and off of the inferior vena cava,

  • allowing more blood to return to the heart.

  • So that's all or most of the functional changes

  • that occur with the cardiovascular system in pregnancy.

  • And the growing uterus also shifts the heart to the left

  • a little, so there are also some anatomical changes, too.

  • Now, I know that's a lot of information,

  • but the cardiovascular system undergoes lots of changes

  • to support the pregnancy.

  • So now let's move on to what changes occur

  • in the respiratory system.

  • So oxygen. Okay.

  • Oxygen consumption increases in pregnancy.

  • Right? The fetus uses oxygen, the mom is using more oxygen

  • to support all the changes in the body.

  • So that means that mom's body needs to

  • bring in more oxygen into the blood.

  • And that's mostly done

  • by increasing minute ventilation.

  • It's mostly done by increasing minute ventilation,

  • or the volume of air

  • that's taken in each minute.

  • And it's not that pregnant ladies

  • intentionally take deeper breaths,

  • because that would get really uncomfortable very quickly.

  • It's all that progesterone once again.

  • So it's all that progesterone in the blood.

  • And what that progesterone does is,

  • it acts on the central respiratory centers

  • in the brain to instruct the lungs

  • to take in more air with each breath.

  • So that's how you end up

  • with more air being taken in

  • with each breath during pregnancy.

  • And a quick thing that needs to be mentioned is that,

  • when you have more air being inhaled with each breath,

  • more carbon dioxide is being exhaled with each breath.

  • Right? Does that make sense?

  • And carbon dioxide is an acid.

  • So in order to keep the pH of the blood balanced,

  • the body responds to that decrease in carbon dioxide,

  • so that decrease in an acid,

  • by increasing the secretion of bicarbonate,

  • which is a base, from the kidneys.

  • So you have increased secretion

  • of bicarbonate from the kidneys.

  • So what you end up with is either normal

  • or a very slightly alkalotic,

  • so a slightly basic, blood pH.

  • Okay. And lastly, there are

  • a couple of anatomical changes, too.

  • So, the enlarging uterus pushes the diaphragm upwards,

  • almost four centimeters through the course of the pregnancy.

  • And that would really make it difficult to breathe.

  • But the chest wall during pregnancy

  • is also more mobile, it's more flexible.

  • And your chest wall circumference is larger.

  • So that works to make up

  • for that upward shift of the diaphragm.

  • Okay, so let's finish off down here

  • by discussing the changes that occur with the kidney.

  • So two things. First thing, we said that there's

  • an increase in blood volume during pregnancy, right?

  • And secondly, all of the arteries in the body

  • are dilated during pregnancy,

  • including the ones that supply the kidney.

  • So if you add those two things up,

  • you end up with having more blood flow to the kidney.

  • And what that means is, you end up with an increase

  • in the rate of filtration of blood through the kidney.

  • It's kind of like, you know those water filters

  • that you can attach directly to your faucet?

  • Right? Imagine if you had one of those.

  • And if your pipes and your faucet got much larger,

  • they got much wider, and there's more water

  • running through the pipes, the rate at which the water

  • was being filtered through the water filter

  • would increase drastically.

  • Well, this is the exact same thing.

  • The kidney is just like your water filter

  • in that it filters all of your blood.

  • Now, with regards to the bladder,

  • there is a contentious topic of whether the bladder

  • holds more or less urine in a pregnant woman.

  • There's some thought that progesterone,

  • which, remember, causes relaxation of smooth muscle,

  • relaxes and increases the capacity of the bladder.

  • And then there's other thought that the pressure

  • of the uterus, the large uterus on the bladder,

  • decreases the capacity of the bladder.

  • So we're not entirely sure.

  • But one thing is certain, and that is that pregnant women

  • definitely urinate more frequently than normal.

  • And that has to do with increased urine production,

  • as well as that pressure on the bladder from the uterus.

  • And that pressure from the uterus

  • also leads to dilatation of the ureter.

  • So the ureters become dilated.

  • And that's really important.

  • And it kind of looks like this,

  • where the pressure from the larger uterus

  • causes the ureters to become wider, to become dilated.

  • And that uterus putting pressure here

  • sort of acts as a road block.

  • And urine builds up in the ureters behind that road block.

  • That built-up stagnant urine

  • acts as a medium for bacterial growth, right?

  • Because we know urinary stasis is a risk factor

  • for bacterial growth.

  • And that's perhaps why pregnant women

  • are more susceptible to developing pyelonephritis,

  • or infection of the kidney,

  • than are non-pregnant women.

  • It's because of that urinary stasis

  • that occurs as a result of the large uterus

  • putting pressure on the ureters.

  • All right. So those are some

  • of the physiologic changes that occur in pregnancy,

  • with the cardiovascular system,

  • the respiratory system, and the renal system.

- You know, there's that saying

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B2 中高級 美國腔

妊娠生理學I (Pregnancy physiology I | )

  • 76 4
    Amy.Lin 發佈於 2021 年 01 月 14 日
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