Pregnancy physiology I | Reproductive system physiology | NCLEX-RN | Khan Academy

Summary

This script delves into the remarkable physiological changes the body undergoes during pregnancy, emphasizing the cardiovascular, respiratory, and renal systems. It highlights how blood volume surges by 40-50% to nourish the fetus, despite blood pressure dropping due to progesterone's vasodilatory effects and the placental circuit. The heart's workload increases, with a faster beat and higher stroke volume. Respiratory adjustments include increased oxygen consumption and minute ventilation, managed by progesterone's influence on brain centers, leading to a slightly alkalotic blood pH. The kidneys experience heightened filtration rates due to increased blood flow, and the urinary system faces challenges like frequency and susceptibility to infections due to ureter dilation and pressure from the growing uterus.

Takeaways

• 🤰 Pregnancy is a complex process that involves significant changes across every organ system to support the growth and development of the fetus.
• 🩸 The cardiovascular system experiences a 40-50% increase in blood volume to meet the oxygen and nutrient demands of the fetus.
• 💓 The heart works harder during pregnancy, beating faster and increasing its stroke volume to pump more blood per minute.
• 📉 Despite the increased cardiac output, blood pressure tends to decrease due to the vasodilatory effects of progesterone and the low-resistance placental circuit.
• 🚫 Progesterone's relaxation of smooth muscle causes blood vessels to dilate, contributing to the drop in blood pressure.
• 🤷‍♀️ Supine Postural Hypotensive Syndrome occurs when the enlarged uterus compresses the inferior vena cava, leading to decreased blood return to the heart and low blood pressure.
• 👶 The respiratory system adapts to pregnancy by increasing oxygen consumption and minute ventilation to meet the needs of the mother and fetus.
• 🌬️ Progesterone influences the central respiratory centers to increase the volume of air inhaled with each breath, without the mother needing to take deeper breaths intentionally.
• 🔄 The kidneys experience increased blood flow and filtration rate due to the overall increase in blood volume and vasodilation during pregnancy.
• 💧 Pregnant women urinate more frequently due to increased urine production and pressure from the enlarging uterus on the bladder.
• 🚨 The pressure from the uterus on the ureters can lead to dilatation and urinary stasis, increasing the risk of kidney infections like pyelonephritis.

Q & A

How does the body demonstrate teamwork during pregnancy?

During pregnancy, the body demonstrates teamwork by having every organ system undergo significant changes to support the growth and development of the fetus while ensuring the mother's body meets its own needs.

What is the primary reason for the increase in blood volume during pregnancy?

The primary reason for the increase in blood volume during pregnancy is to carry more oxygen and nutrients to the fetus, which increases by about 40 to 50 percent.

How does the heart adapt to the demands of pregnancy?

The heart adapts by beating more quickly, increasing the stroke volume, and thus the cardiac output, to supply more blood to meet the demands of the fetus.

Why does blood pressure decrease during pregnancy despite the increased cardiac output?

Blood pressure decreases due to the relaxing effect of progesterone on smooth muscle, including blood vessels, causing dilation and lowered blood pressure. Additionally, the placenta acts as a low-resistance circuit, contributing to the decrease.

What is Supine Postural Hypotensive Syndrome and how is it related to pregnancy?

Supine Postural Hypotensive Syndrome occurs when the enlarged uterus compresses the inferior vena cava in the supine position, leading to decreased blood return to the heart and causing low blood pressure and lightheadedness.

How does oxygen consumption change during pregnancy?

Oxygen consumption increases during pregnancy due to the fetus's needs and the mother's body changes, leading to an increase in minute ventilation to bring in more oxygen.

What role does progesterone play in respiratory changes during pregnancy?

Progesterone acts on the central respiratory centers in the brain to increase minute ventilation, causing pregnant women to take in more air with each breath.

How does the body maintain blood pH balance when carbon dioxide levels decrease due to increased ventilation?

The body maintains blood pH balance by increasing the secretion of bicarbonate, a base, from the kidneys to counteract the decrease in carbon dioxide, an acid.

What anatomical changes occur in the respiratory system during pregnancy?

The enlarging uterus pushes the diaphragm upwards, but the chest wall becomes more mobile and flexible, and the chest wall circumference increases to compensate for the upward shift of the diaphragm.

How does pregnancy affect the kidneys and the urinary system?

Pregnancy increases blood flow to the kidneys, leading to an increased rate of filtration. Pregnant women also urinate more frequently due to increased urine production and pressure from the uterus on the bladder. The ureters may dilate, which can lead to urinary stasis and a higher risk of kidney infections.

Outlines

00:00

💓 Cardiovascular Changes in Pregnancy

This paragraph discusses the significant changes in the cardiovascular system during pregnancy. The body requires more blood to supply oxygen and nutrients to the fetus, leading to a 40-50% increase in blood volume. The heart compensates by beating faster, about 10-15 beats per minute more than usual, and increasing its stroke volume. Despite these efforts, blood pressure actually decreases due to the relaxing effects of progesterone on blood vessels and the presence of the low-resistance placental circuit. The paragraph also introduces Supine Postural Hypotensive Syndrome, which occurs when the enlarged uterus compresses the inferior vena cava, reducing blood return to the heart and causing hypotension. Relief can be found by changing the mother's position to the left side.

05:03

🌬️ Respiratory and Renal Adaptations in Pregnancy

The second paragraph delves into the respiratory system's adaptations to pregnancy, where oxygen consumption increases to support both the mother and the fetus. The body achieves this by increasing minute ventilation, or the volume of air inhaled per minute, through the influence of progesterone on the brain's respiratory centers. This leads to more air intake and, consequently, more carbon dioxide exhalation, which the body counteracts by increasing bicarbonate secretion from the kidneys to maintain blood pH balance. Anatomical changes include the uterus pushing the diaphragm upwards, but the chest wall's increased mobility and size help compensate for this. The paragraph also covers renal changes, where increased blood volume and vasodilation lead to heightened kidney filtration rates. The bladder's capacity is a topic of debate due to conflicting effects of progesterone and uterine pressure, but increased urination is a consistent observation. Lastly, the uterus's pressure on the ureters can cause dilation and urinary stasis, increasing the risk of kidney infections like pyelonephritis.

10:04

🤰 Overview of Physiological Changes in Pregnancy

The final paragraph offers a brief overview of the physiological changes that have been discussed, focusing on the cardiovascular, respiratory, and renal systems. It summarizes the key points made in the previous paragraphs, emphasizing the body's remarkable adaptations to support the growing fetus and the health of the pregnant woman.

Keywords

💡Cardiovascular System

The cardiovascular system, comprising the heart and blood vessels, is central to the body's ability to supply oxygen and nutrients to the fetus during pregnancy. In the video, it's explained that blood volume increases by 40 to 50 percent, and the heart works harder, beating more quickly and pumping more blood with each beat to meet the increased demands. This system's changes are crucial for fetal development and maternal health.

💡Blood Volume

Blood volume refers to the total amount of blood circulating in the body. The script mentions that during pregnancy, blood volume increases significantly, which is vital for transporting oxygen and nutrients to the fetus. This increase is a key physiological adaptation to pregnancy, ensuring that both the mother and the developing baby receive adequate blood supply.

💡Progesterone

Progesterone is a hormone that plays a significant role in pregnancy. As described in the video, it causes the relaxation of smooth muscle, including that of blood vessels, leading to dilation and a consequent decrease in blood pressure. This hormonal change is part of the body's complex response to pregnancy, affecting various systems including the cardiovascular and urinary systems.

💡Blood Pressure

Blood pressure is the force exerted by circulating blood on the walls of blood vessels. Contrary to common assumptions, the video explains that blood pressure actually decreases during pregnancy due to the effects of progesterone and the presence of the placenta. This decrease is a normal physiological change that helps to ensure adequate blood flow to the uterus.

💡Supine Postural Hypotensive Syndrome

This syndrome, as mentioned in the video, occurs when the enlarging uterus compresses the inferior vena cava in the supine position, reducing blood return to the heart and leading to low blood pressure and symptoms like lightheadedness. It's an example of how the physical changes of pregnancy can impact the body's normal functions and is a reminder of the importance of proper posture during pregnancy.

💡Respiratory System

The respiratory system's role in pregnancy is highlighted by the need for increased oxygen consumption to support the fetus. The video explains that the body compensates by increasing minute ventilation, or the volume of air inhaled per minute, primarily through the action of progesterone on the brain's respiratory centers. This adaptation is essential for maintaining adequate oxygen levels in the blood.

💡Minute Ventilation

Minute ventilation is the total volume of air inhaled and exhaled by the lungs per minute. The video describes how it increases during pregnancy to meet the oxygen demands of the mother and fetus. This increase is facilitated by hormonal changes, specifically progesterone, which instructs the lungs to take in more air, ensuring sufficient oxygenation.

💡Kidney

The kidneys play a critical role in filtering blood and regulating electrolytes and fluid balance. In the context of the video, it's noted that blood flow to the kidneys increases during pregnancy due to the overall increase in blood volume and vasodilation. This results in a higher rate of filtration, which is essential for maintaining the body's homeostasis during the significant physiological changes of pregnancy.

💡Ureters

Ureters are the tubes that carry urine from the kidneys to the bladder. The video explains that they can become dilated during pregnancy due to pressure from the enlarging uterus. This dilation can lead to urinary stasis, increasing the risk of urinary tract infections such as pyelonephritis. The ureters' changes are a significant aspect of the renal system's adaptation to pregnancy.

💡Bladder

The bladder's capacity and function are impacted by pregnancy, as discussed in the video. There's a debate over whether the bladder's capacity increases due to progesterone's relaxing effects or decreases due to pressure from the uterus. Regardless, the frequency of urination increases, which is a common and expected change that can be attributed to both increased urine production and the physical pressure exerted by the growing uterus.

Highlights

The human body's organs work in unison to support fetal growth and development, illustrating remarkable teamwork.

Every organ system undergoes significant changes during pregnancy to accommodate the needs of the growing fetus.

Blood volume increases by 40 to 50 percent to supply more oxygen and nutrients to the fetus.

The heart works harder, beating 10 to 15 times more per minute and increasing stroke volume to meet fetal demands.

Despite the increased cardiac output, blood pressure during pregnancy actually decreases due to progesterone's vasodilatory effects.

The placenta acts as a low-resistance circuit in the circulatory system, contributing to the decrease in blood pressure.

Supine Postural Hypotensive Syndrome occurs when the enlarged uterus compresses the inferior vena cava, leading to hypotension.

Turning to the left side can quickly alleviate the symptoms of Supine Postural Hypotensive Syndrome by reducing pressure on the inferior vena cava.

The growing uterus causes the heart to shift to the left, indicating anatomical changes in the cardiovascular system during pregnancy.

Oxygen consumption increases in pregnancy, necessitating an increase in minute ventilation to supply more oxygen to the blood.

Progesterone influences the central respiratory centers to increase air intake, leading to more oxygen and carbon dioxide exchange.

To maintain blood pH balance, the kidneys increase bicarbonate secretion in response to increased carbon dioxide exhalation.

The enlarging uterus pushes the diaphragm upwards, affecting respiratory mechanics, but the chest wall's increased mobility compensates for this.

Blood flow to the kidneys increases due to the overall blood volume expansion and arterial dilation during pregnancy.

The rate of blood filtration through the kidneys rises, similar to how a water filter works when water flow is increased.

The debate on whether the bladder holds more or less urine during pregnancy is due to conflicting effects of progesterone and uterine pressure.

Pregnant women urinate more frequently due to increased urine production and pressure from the enlarging uterus on the bladder.

Dilatation of the ureters due to uterine pressure can lead to urinary stasis, increasing the risk of pyelonephritis in pregnant women.

Transcripts

- 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.