Respiratory System, Part 2: Crash Course Anatomy & Physiology #32

Summary

The video explains how hyperventilation and respiration affect the body's homeostasis, focusing on the role of oxygen and carbon dioxide. It details how hemoglobin binds oxygen and how factors like partial pressure, acidity, temperature, and CO2 levels influence gas exchange in the blood. The video also explores how hyperventilation disrupts this balance, leading to hypocapnia, and explains why breathing into a paper bag restores normalcy. The key takeaway is how intricate the respiratory system is and how maintaining homeostasis is crucial for optimal function, especially in stressful situations like giving a big presentation.

Takeaways

• 😨 Anxiety during stressful situations, like giving a presentation, can cause hyperventilation, leading to a drop in CO2 levels and an imbalance in the body.
• 🫁 Breathing into a paper bag during hyperventilation helps restore CO2 levels, bringing the body back to homeostasis.
• 💡 Carbon dioxide plays a crucial role in maintaining homeostasis in the body, affecting blood pressure, pH levels, and temperature.
• 🧠 Hemoglobin’s affinity for oxygen changes depending on conditions like temperature, CO2 levels, and acidity, to help regulate oxygen delivery.
• 🧪 Partial pressure gradients of oxygen help move oxygen from areas of high pressure, like in the lungs, to areas of low pressure, like in tissues.
• ⛰️ High altitudes, like on Mt. Everest, make it difficult to breathe due to lower air pressure, reducing the partial pressure of oxygen.
• 🔥 Metabolically active tissues like muscles generate heat and CO2, which lower hemoglobin’s affinity for oxygen, helping release more oxygen where it's needed.
• 🩸 CO2 dissolving in blood forms carbonic acid, which helps lower blood pH and trigger oxygen release, further supporting tissue oxygenation.
• 🔁 Hemoglobin binds to oxygen in the lungs and releases it in tissues, then picks up CO2 for removal via exhalation.
• 🎓 Understanding the exchange of gases like oxygen and CO2 in the body is key to maintaining homeostasis and responding effectively to physical stress.

Q & A

What happens to your body when you start hyperventilating before a presentation?

When you hyperventilate, you exhale more CO2 than you should, which causes a drop in CO2 levels (hypocapnia), leading to light-headedness and other symptoms as your body struggles to maintain balance.

Why is carbon dioxide as important as oxygen in maintaining homeostasis?

Carbon dioxide helps regulate blood pressure, pH levels, and temperature, all of which are crucial for maintaining the body's internal balance.

How does breathing into a paper bag help during hyperventilation?

Breathing into a paper bag allows you to re-inhale the CO2 you exhaled, raising CO2 levels in your blood, lowering pH, and helping restore homeostasis.

What is partial pressure, and why is it important for oxygen exchange in the body?

Partial pressure refers to the pressure exerted by a single gas in a mixture, and it drives the movement of oxygen from the lungs into the blood due to differences in oxygen concentration and pressure.

How does hemoglobin's affinity for oxygen change in different parts of the body?

Hemoglobin's affinity for oxygen decreases in areas like active muscles, where oxygen is needed most, allowing hemoglobin to release oxygen more easily.

What role do heat and CO2 play in oxygen release from hemoglobin?

Heat and CO2 change the shape of hemoglobin, lowering its affinity for oxygen and encouraging more oxygen release in active tissues.

How does low pH affect hemoglobin and oxygen delivery?

Low pH, caused by an increase in CO2, changes hemoglobin's shape and promotes oxygen release, especially in active tissues that need more oxygen.

Why does breathing become harder at high altitudes?

At high altitudes, the partial pressure of oxygen is much lower, making it harder for oxygen to enter the bloodstream due to the lack of a strong pressure gradient.

How do proteins like hemoglobin change shape when binding to molecules?

When hemoglobin binds to oxygen, it changes shape, increasing its affinity for additional oxygen molecules, a process known as cooperativity.

What happens to hemoglobin when oxygen binds to it in the lungs?

When oxygen binds to hemoglobin in the lungs, hemoglobin changes shape, making it easier for more oxygen to attach, and the molecule becomes oxyhemoglobin, ready to transport oxygen to tissues.

Outlines

00:00

😰 Overcoming Presentation Anxiety

The speaker paints a vivid picture of a person preparing for a big presentation but is overwhelmed by anxiety. They imagine worst-case scenarios like losing their train of thought or fainting. This leads to hyperventilation, where the person exhales too much CO2, throwing their internal balance off. Luckily, breathing into a paper bag helps restore this balance by reintroducing CO2, calming them down. The importance of CO2 in maintaining homeostasis, especially in the blood, is introduced.

05:03

🩸 The Role of Hemoglobin in Oxygen Transport

This paragraph discusses the essential role hemoglobin plays in the blood's ability to transport oxygen. Hemoglobin binds to oxygen when partial pressure conditions are right, allowing for gas exchange between the blood and tissues. This balance is critical for bodily functions, including performing strenuous activities like climbing a mountain. Hemoglobin's ability to carry and release oxygen is influenced by the partial pressure of oxygen in the environment and the blood.

10:06

🌡️ Temperature and CO2 Impact on Oxygen Delivery

Here, the script explains how temperature and carbon dioxide (CO2) affect hemoglobin’s ability to release oxygen to tissues. Active tissues, like muscles during exercise, heat up, which lowers hemoglobin’s affinity for oxygen, allowing it to release more oxygen where it’s needed. CO2 further lowers this affinity, prompting hemoglobin to release oxygen and bind with CO2. This coordinated process ensures that oxygen is delivered efficiently, especially during physical activity.

🌬️ CO2 and Blood Acidity's Role in Gas Exchange

This part covers how an increase in CO2 during muscle activity makes the blood more acidic, which further promotes the release of oxygen from hemoglobin. The blood carries CO2 back to the lungs, where new oxygen inhaled binds to hemoglobin, restarting the process of gas exchange. Hemoglobin’s shape and affinity for gases change depending on the surrounding conditions, ensuring effective oxygen delivery and CO2 removal.

💼 Managing Stress and Hyperventilation

Returning to the earlier scenario, the paragraph explains how hyperventilation during anxiety leads to a loss of CO2, raising blood pH and causing vasoconstriction, which limits blood flow to the brain. This causes light-headedness. Breathing into a paper bag helps reintroduce CO2 into the bloodstream, lowering pH and restoring balance. This illustrates how physiological responses can sometimes misfire during stress, but simple interventions can correct the issue.

📚 Crash Course Acknowledgements and Production Team

The script concludes by acknowledging the contributions of the Crash Course Patreon community and the production team behind the episode. It names key individuals involved in the writing, directing, and editing processes, highlighting their roles in making the video possible.

Keywords

💡Hyperventilation

Hyperventilation refers to breathing too rapidly and exhaling more CO2 than the body produces. This lowers CO2 levels in the blood, leading to symptoms like light-headedness and fainting. In the video, this occurs when someone gets nervous before a presentation, highlighting the physiological effects of stress and breathing on homeostasis.

💡Homeostasis

Homeostasis is the body’s ability to maintain internal balance, such as regulating oxygen and carbon dioxide levels in the blood. The video explains how hyperventilation disrupts this balance, causing physiological changes like vasoconstriction. Restoring CO2 levels with a paper bag helps return the body to homeostasis, ensuring stable function.

💡Partial Pressure

Partial pressure refers to the pressure exerted by a specific gas in a mixture of gases, like oxygen in air. In the video, this concept explains how oxygen moves from areas of high to low pressure, allowing oxygen to diffuse from the lungs into the bloodstream. It’s also why breathing becomes difficult at high altitudes, as the partial pressure of oxygen decreases.

💡Hemoglobin

Hemoglobin is a protein in red blood cells that binds to oxygen for transport through the body. The video explains how hemoglobin’s affinity for oxygen changes depending on the environment, such as releasing oxygen in low-pressure areas like muscle tissue. Hemoglobin also binds CO2 when oxygen is released, playing a key role in gas exchange.

💡Cooperativity

Cooperativity refers to how the binding of one molecule (like oxygen) to hemoglobin makes it easier for other molecules to bind. The video compares this to a social situation, where once hemoglobin binds one oxygen molecule, it quickly attracts more until fully saturated. This process ensures efficient oxygen transport and delivery to tissues.

💡Carbon Dioxide (CO2)

Carbon dioxide is a waste product produced by cells and is carried in the blood to the lungs for exhalation. The video emphasizes CO2’s role in regulating blood pH and oxygen delivery. When CO2 levels drop during hyperventilation, the body’s pH rises, causing vasoconstriction and reducing oxygen delivery to the brain, explaining the feeling of light-headedness.

💡pH Balance

The pH balance refers to the acidity or alkalinity of the blood, which is regulated by CO2 levels. The video explains how hyperventilation reduces CO2, raising blood pH and causing vasoconstriction. Maintaining a proper pH is essential for oxygen delivery, as hemoglobin’s affinity for oxygen changes with pH levels, affecting oxygen release in tissues.

💡Vasoconstriction

Vasoconstriction is the narrowing of blood vessels, which reduces blood flow. In the video, it occurs during hyperventilation due to increased blood pH, leading to less oxygen reaching the brain, which causes dizziness. Vasoconstriction is part of the body's stress response, diverting blood to essential areas, but it can be harmful during hyperventilation.

💡Oxyhemoglobin

Oxyhemoglobin refers to hemoglobin that has bound to oxygen. In the video, oxyhemoglobin is formed when hemoglobin binds to oxygen in the lungs and is then transported to tissues. This molecule plays a critical role in oxygen delivery, and its ability to release oxygen is influenced by factors like partial pressure, temperature, and CO2 levels.

💡Sympathetic Nervous System

The sympathetic nervous system is part of the body's autonomic response to stress, preparing it for 'fight or flight.' In the video, it is activated when someone gets nervous before a presentation, increasing heart rate and breathing. This response is helpful in emergencies but leads to hyperventilation and disruptions in gas exchange when there's no physical danger.

Highlights

You're about to give a big presentation, but anxiety makes you forget how to speak and you start hyperventilating.

Hyperventilation leads to an imbalance of oxygen and carbon dioxide, affecting blood pressure, pH, and temperature.

Breathing into a paper bag helps restore CO2 levels and balance your respiratory system, preventing fainting.

Hypocapnia occurs when you exhale too much CO2, breaking the exchange of gases needed for homeostasis.

Hemoglobin's affinity for oxygen isn't constant; it changes depending on the environment, allowing oxygen to bind or release.

Partial pressure is key in gas exchange, with oxygen moving from areas of high to low pressure, such as from air into blood.

At sea level, the partial pressure of oxygen is 160 mmHg, but it drops to 45 mmHg on Mount Everest, making breathing difficult.

Hemoglobin changes shape when binding with oxygen, which increases its affinity for more oxygen, a process called cooperativity.

Oxygen is released from hemoglobin in areas of low oxygen partial pressure, like active tissues, due to metabolic demands.

Heat and CO2 from metabolic activity also trigger oxygen release by lowering hemoglobin's affinity for it.

CO2 binding to hemoglobin helps trigger oxygen release, while also facilitating the transport of CO2 back to the lungs.

Increased CO2 in the blood makes it more acidic, further lowering hemoglobin’s affinity for oxygen and enhancing oxygen delivery.

During stress or hyperventilation, your body's lack of CO2 causes blood pH to rise, leading to vasoconstriction and light-headedness.

Breathing into a paper bag raises the CO2 level in your blood, restoring pH balance and preventing vasoconstriction.

Understanding partial pressure, blood acidity, and temperature helps explain how your body manages oxygen delivery and CO2 removal.

Transcripts

Picture this: You’re getting ready to give a big presentation in front of, like, a lot

of important people. You’re practicing in front of your mirror, and then just for a

second you forget how to speak.

Suddenly, you feel that familiar sting of anxiety, like an icy hand on the back of your neck.

You look at yourself in that mirror and you start imagining some of the worst, worst-case

scenarios. Like, what if you totally lose your train of thought up there? What if you

barf? What if everybody gets up and leaves? Now you’re really nervous. I’m getting

freaked out just talking about it.

So ou start taking quick, shallow breaths, and you’re feeling light-headed, and seeing

stars, and now you, my friend, are hyperventilating.

When we talk about respiration, we tend to focus on oxygen -- and who could blame us?

It’s easy to forget the equally important role that carbon dioxide plays in maintaining

homeostasis. Your internal balance between oxygen and carbon dioxide factors heavily

into all sorts of stuff -- especially in your blood, where it can affect your blood’s

pressure, its pH level, even its temperature.

And now -- at, like, T-minus 5 minutes to your presentation -- all of those things are

out of whack, because you’re exhaling more CO2 than you should.

You’re just about to faint, when a friend suddenly hands you a paper bag to breathe

into. And you’ve never been so grateful for a lunch bag in your life, because, somehow,

it does the trick.

Within seconds, you’re back to normal.

The drop in CO2 that occurs in your blood when you hyperventilate is called hypocapnia,

and it signals a breakdown in one of the most complex and important functions that your

respiratory system performs.

That is: the exchange of gases inside your blood cells, where the stuff your body doesn’t

want is swapped out for what it desperately needs.

This exchange -- between carbon dioxide and oxygen -- is regulated by a whole series of

biological signals that your blood cells use to communicate with your tissues, about what

they have, what they want, and what they need to get rid of.

It’s almost like a code, one that’s written into your blood’s chemistry, in the folding

of its proteins -- even in its temperature and acidity.

It’s what allows you to perform strenuous physical tasks, like climbing a mountain.

It’s also what lets you reboot your whole respiratory system, with nothing more than a paper bag.

I’ll admit it: when we’ve talked about the chemistry of your blood so far, we’ve

tended to keep things pretty simple.

Like, hemoglobin contains four protein chains, each of which contains an iron atom; since

iron binds readily with oxygen, that’s how hemoglobin transports oxygen around your body.

Ba-da-bing.

But the fact is, hemoglobin’s affinity for oxygen isn’t always the same.

In some places, we want our hemoglobin to have a high affinity for oxygen, so it can

easily grab it out of the air. And in others, we want it to have

a low affinity for oxygen oxygen, so it can dump those molecules to feed our cells.

So how does your hemoglobin know when to collect its precious cargo and when to let it go?

Well, a lot of it has to do with a principle of chemistry known as partial pressure.

One of the things that fluids always do is move from areas of high pressure to low pressure.

And molecules also diffuse from areas of high concentration to areas of low concentration.

But when we talk about gases in a mixture, we need to combine the ideas of pressure and concentration.

See, air is a mixture of molecules. And when you’re studying the respiratory system,

you often need to focus on the oxygen, which makes up about 21% of it.

But that doesn’t tell us how many oxygen molecules there are. For that, we need to

know the overall air pressure, since more molecules in a certain volume means more pressure.

So, partial pressure gives us a way of understanding how much oxygen there is,

based on the pressure that it’s creating.

Example: The pressure of air at sea level is about 760 millimeters of mercury. But since

only about 21 percent of that air is oxygen, oxygen’s part of that pressure -- or partial

pressure of oxygen -- is 21% of 760, or about 160 millimeters of mercury.

Now, that’s just outside, at sea level.

When that air mixes with the air deep in your lungs -- including a lot of air that you haven’t

exhaled yet -- the partial pressure of oxygen drops to about 104 millimeters of mercury.

And in the blood that’s entering your lungs -- after most of its oxygen has been stripped

away by your hungry muscles and neurons -- the oxygen partial pressure is only about 40 millimeters.

This big differences in pressure make it easy for oxygen molecules to travel from the outside air into

your blood plasma, because, as a rule dissolved gases always diffuse down their partial pressure gradients.

This is why it’s so much harder to breathe at higher altitudes. When you climb a mountain,

the concentration of oxygen stays at about 21%. But the pressure gets lower, which means the

partial pressure of oxygen also decreases to about 45 millimeters of mercury at the top of Mt. Everest.

So the partial pressure of oxygen at the top of the highest peak in the world, is almost

the same as the de-oxygenated blood that’s entering your lungs.

So basically there is no partial pressure gradient, which makes it really hard to get

oxygen into your blood. But, let’s get back to the red blood cells.

Remember that the globin in your hemoglobin is a protein -- and when proteins bind to

stuff, they tend to change shape. And that shape-change can make the protein more or

less likely to bind to other stuff.

When an empty hemoglobin runs into an oxygen molecule, things are a little awkward.

It’s like a first date -- bonding isn’t so easy.

But once they finally bind, hemoglobin suddenly changes shape, which makes it easier for other

oxygen molecules to attach, like friends gathering around the lunch table.

That affinity for joining in -- or cooperativity, as it’s known -- continues until all four

binding sites are taken, and the molecule is fully saturated.

Now your hemoglobin is known as oxyhemoglobin, or HbO2. It is not...not why the cable network

is called that. That’s the “Home Box Office.” Anyway.

By the time the blood leaves the lungs, each hemoglobin is fully saturated, the oxygen

partial pressure in your plasma is about 100 millimeters, and now it is ready to be delivered

to where it is needed most.

Active tissues, like the brain, heart, and muscles, are always hungry for oxygen. They

burn through it quickly, lowering the oxygen partial pressure around them to about 40 millimeters.

So when the blood arrives on the scene, oxygen moves down the gradient from the plasma to

the tissues, to feed those hungry cells.

That makes the oxygen partial pressure in your plasma drop, so your hemoglobin starts

to give up more of its oxygen to the plasma.

BUT! Partial pressures are only part of what’s prodding your hemoglobin to give up the goods.

All of that metabolic activity going on in your tissues is also producing other triggers,

in the form of waste products -- specifically heat and CO2.

Both of those things activate the release of more oxygen, by lowering hemoglobin’s affinity for it.

Say you’re climbing that mountain again, and your thighs are feeling the burn. Red

blood cells saturated with oxygen are going to the muscle tissue in your quads, where

the hemoglobin can dump a bunch of O2, because of the lower partial pressures of oxygen in your muscles.

But a hard-working quad will also heat up the surrounding tissues, and that rise in

temperature changes the shape of hemoglobin -- and it does it in such a way that lowers its affinity for O2.

So when those red blood cells hit that warm active tissue, they release even more oxygen

-- like 20 percent more -- beyond what partial pressures would trigger.

But wait! There’s more!

Carbon dioxide triggers the release of oxygen, too, because it also binds to the hemoglobin,

changing its shape again, lowering its affinity for oxygen still more. And as oxygen jumps

ship, the hemoglobin can pick up more CO2.

Finally, JUST IN CASE the hemoglobin isn’t getting the message at this point, there’s

one more trigger that your respiratory system has up its sleeve. The spike in CO2 that’s

released by your active muscle tissues actually makes your blood more acidic.

Since your blood is mostly water, when CO2 dissolves in it, it forms carbonic acid, which

breaks down into bicarbonate and hydrogen ions. Those ions bind to the hemoglobin, changing

its shape yet again, further lowering its affinity for oxygen.

So now, at last, your tissues have the oxygen they need, and your red blood cells are stuck

with all this CO2 that they need to get rid of.

Your red blood cells ride the vein-train back to the lungs,

where they encounter a new wave of freshly inhaled oxygen.

And when that O2 binds to the hemoglobin -- which, again, is hard at first -- it eventually changes

its shape back to the way it was when we started, which decreases its affinity for CO2.

So the hemoglobin drops its carbon dioxide, which moves down its partial pressure gradient

into the air of your lungs, so you can exhale it, and the whole thing can start all over again.

Now if that isn’t enough to make you hyperventilate, I’m not sure what is.

But this brings us back to that unfortunate episode you had before your big presentation.

This whole complex code of chemical signals that I just described? Well, it assumes that

what your cells and tissues are telling each other is actually true.

But as we all know, sometimes our bodies don’t mean what they say. Thanks, body.

Like, when you’re freaking out about your presentation, your sympathetic nervous system

makes your heart race and your breathing increase, to prepare you to fight or flee.

The problem is: there’s nothing to actually fight or flee from, so your muscles aren’t

actually doing anything, so they’re not using all the extra oxygen you’re breathing in.

And they also aren't producing the extra CO2 that you're suddenly exhaling all over the place.

So when you start to exhale CO2 faster than your cells release it, its concentration in

your blood drops. And with less carbonic acid around, your blood’s pH starts to rise.

And you know what else? While low blood pH does things like change the shape of your

hemoglobin to deliver oxygen, high pH causes vasoconstriction.

Normally, this is supposed to divert blood from the parts you’re not using during times

of stress, like your digestive organs, to the parts that you are using.

But when you hyperventilate, this constriction happens everywhere, which means less blood

is delivered to your brain, which makes you light-headed.

Luckily, that trick with the breathing into the paper bag -- it really does work.

It works because it lets you breathe back in all of the CO2 you just breathed out. So

the partial pressure of carbon dioxide in the bag is higher, which forces that CO2 into

your blood, which lowers its pH, and you get back to homeostasis.

And of course, homeostasis is the key to life...and you know, also to a successful presentation.

If you were able to remain calm today, you learned how your blood cells exchange oxygen

and CO2 to maintain homeostasis. We talked about partial pressure gradients, and how

they, along with changes in blood temperature, acidity, and CO2 concentrations, change how

hemoglobin binds to gases in your blood. And you learned how the thing with the bag works.

Of course, we must say thank you to our patrons on Patreon who help make Crash Course possible through

their monthly contributions, not just for themselves, but for everyone. If you like Crash Course and want to

help us keep making videos like this one, you can go to patreon.com/crashcourse.

This episode was filmed in the Doctor Cheryl C. Kinney Crash Course Studio, it was written

by Kathleen Yale, the script was edited by Blake de Pastino, and our consultant is Dr.

Brandon Jackson. It was directed and edited by Nicole Sweeney; our sound designer is Michael

Aranda, and the graphics team is Thought Cafe.