062 Pressure Changes during Breathing

062 Pressure Changes during Breathing

Leslie Samuel IBTV, Physiology, The Respiratory System 89 Comments

Breathing is one of the most common things we do everyday to a point that it becomes unnoticed. Wouldn’t it be great to learn what happens behind this process? What exactly happens when we breathe air in and out of our body? Watch this video as Leslie teaches once again in such an easy way to make it all easy for us to understand this concept.

Have fun!

Transcript of Todays Episode

Hello and welcome to another episode of Interactive-Biology TV where we’re making Biology fun. My name is Leslie Samuel. In this episode, Episode 62, I’m going to be talking about pressure changes that happen during breathing. That’s what we’re going to talk about. Let’s just get right into it.

We’ve been talking about the respiratory system. We have been talking about the fact that you are breathing in. As air comes in, so let’s say the air is coming through here and then, it eventually ends up in the lungs. In the lungs, we can see here we have the alveoli. As the air comes in, that air can then give oxygen to the blood and it can take carbon dioxide and bring that into the cavity here and then, when you breathe out, of course, that air is going to go through the mouth and through the nose, depending on how you’re breathing and that’s going to push the air outside.

What we’re going to talk about is how this process of breathing actually happens and the pressure changes that are involved.

Here we have the two lungs. What I’m going to do is I’m going to draw an additional part here because this diagram is kind of simplified so, we’re just going to add a little more. We’re going to close this off and we are going to close that part off. And then, I’m going to give some names.

This entire section that we’re dealing with, that is called the thoracic cavity. In the thoracic cavity, we have this space right here. That space is called the pleural cavity. Then, we have one more cavity and that’s inside the lungs. We’re going to call that the pulmonary cavity. Another thing that we need to label here, this here is a muscle and that muscle we call the diaphragm. Beneath here we have the abdominal cavity but, we’re not going to talk too much about that. Actually, let me still label it here because we are going to mention it. Abdominal cavity.

What we’re going to talk about is what happens during breathing. Over here we’re looking at muscles and here you can see we have this group of muscles here and that is called the external intercostals. You can see it diagonally going here. Then, here we have the internal intercostals muscles. So, we’re going to talk about the things that happen during breathing and we’re going to mention what roles those play also.

When I’m breathing in, I’m taking a breath. I just breathe in. There are a number of things that are happening.

First thing is we have the diaphragm here and the diaphragm contracts. When the diaphragm contracts, that moves down. It kind of moves down here. Then, we have the external intercostals. When they contract, that moves the rib cage up. So the diaphragm is contracting; the external intercostals are contracting; this moves down, the external intercostals move the rib cage up and the overall effect is that we’re increasing the space of the thoracic cavity. So, we’re increasing the size of the thoracic cavity. When you increase the size, that is going to cause a decrease in pressure in the thoracic cavity. Of course, since you’re increasing the size and you’re pushing down here with the diaphragm, it’s increasing the pressure in the abdominal cavity, decreasing the pressure in the thoracic cavity. Of course then, that’s going to cause a reduction in pressure of the pleural cavity. When the pressure is reduced in the pleural cavity, that then becomes lower than the pressure inside the lungs in the pulmonary cavity.

Once again, diaphragm contracts, external intercostals contract. That expands the thoracic cavity, decreasing the pressure in the pleural cavity. If we have a lower pressure in here than in the lungs, what is going to happen to the lungs? Of course, greater pressure inside, lower pressure on the outside, the lungs are going to expand. As the lungs expand, now you have more space in here, that’s going to decrease the pressure in the pulmonary cavity, relative to the pressure of the atmosphere. That is going to cause air to move from higher pressure to lower pressure and the air is going to go in and, of course, go into the lungs.

Let’s review that again: Diaphragm contracts, external intercostals contract that expands the thoracic cavity, decreasing the pressure in the pleural cavity. Because that’s going to be now lower than the pulmonary cavity, that’s going to cause the lungs to expand causing a reduction in pressure in the pulmonary cavity. That’s going to cause air to move from the atmosphere into the lungs. And, we have just accomplished breathing in.

During normal breathing, what then happens when it’s time to, not inspire, but expire, so, exhale. The diaphragm and the external intercostal muscles are going to relax. Since we had a buildup in pressure here, when the diaphragm contracted, the abdominal cavity is then going to push against the thoracic cavity increasing the pressure in the pleural cavity, increasing the pressure in the pulmonary cavity causing air to leave. So, it’s the exact opposite.

First, we’re decreasing the pressure by expanding then, now we are increasing the pressure by making the cavity smaller, pushing the air out. That’s during normal breathing.

When you are breathing more intense and it’s more of a forced breathing situation, it’s very similar to what we just described except that there are other muscles involved. So, for inspiration, the diaphragm is going to contract, external intercostals are going to contract and also some neck muscles and we’re going to get air coming in. It’s a stronger contraction. So, that’s going to bring more air in because you’re reducing the pressure even more.

Then, when you’re breathing out, you’re not just relaxing the diaphragm but you’re also bringing in the internal intercostals muscles and those are going to contract and when those contract, the rib cage moves down, thoracic cavity gets smaller, faster of course, and that’s going to increase pressure faster, and cause more air to be pushed out into the atmosphere.

Overall, you’re breathing in because you’re decreasing the pressure on the inside, you’re breathing out because you’re increasing the pressure on the inside.

That’s pretty much all for this episode. As usual, if you want to find more of these videos and other resources I’d like to invite you to visit the website at Interactive-Biology.com. That’s it for this video and I’ll see you on the next one.

Comments 89

  1. RS

    Is it possible for you to make a video topic that just covers ‘ACID BASE’. For instance, Metabolic alkalosis, Respiratory Alkalosis? You are doing a wonderful job with these videos. It will be nice of you if you please cover the acid base topic in the Respiratory system. Thanks

    1. Post
      Author
      Lrsamuel

      Thanks for your comment. In terms of the videos, I make them as I need them for the classes I’m going to be teaching. If that ever comes up, I’ll make a video about it.

      All the best!

  2. oneaware

    Leslie, I found your website and it’s been a tremendous help for me in nursing school. It is an excellent review of basic physiology that is actually understandable. God bless.

  3. oneaware

    Leslie, I found your website and it’s been a tremendous help for me in nursing school. It is an excellent review of basic physiology that is actually understandable. God bless.

  4. InteractiveBiology

    You’re very much welcome. Do stay tuned for more as Leslie plans to put up more Biology videos coming very soon.

  5. InteractiveBiology

    Glad to know that. :) Leslie is indeed a great teacher! You can keep on learning more Biology stuff from our website. There will be more videos that will be uploaded so, please stay tuned!

  6. InteractiveBiology

    You’re welcome! We’re glad to know you’re finding value in them. Stay tuned! We have new Biology videos coming soon!

    1. Post
      Author
  7. AGirlFromDownUnder

    During inspiration, you breathe in and air enters your lungs, so they expand.

    There is always air inside your lungs, even when you breathe out as much as you can :)

  8. AGirlFromDownUnder

    Ext. Intercostals actually move up AND outwards.
    Also, in forced inspiration (when you take a breath on purpose or are breathing hard), serratus anterior becomes involved as well as the sternocleomastoid, Scalene muscles and the laryngeal/pharyngeal muscles. These are not used at rest!
    In forced expiration, the abdominal muscles come into play (int./ext. obliques, transversus abdominus and rectus abdominus (‘Six-pack’ muscles).
    At rest, expiration is passive and occurs due to elastic recoil.

  9. AGirlFromDownUnder

    Ext. Intercostals actually move up AND outwards.
    Also, in forced inspiration (when you take a breath on purpose or are breathing hard), serratus anterior becomes involved as well as the sternocleomastoid, Scalene muscles and the laryngeal/pharyngeal muscles. These are not used at rest!
    In forced expiration, the abdominal muscles come into play (int./ext. obliques, transversus abdominus and rectus abdominus (‘Six-pack’ muscles).
    At rest, expiration is passive and occurs due to elastic recoil.

  10. AGirlFromDownUnder

    Ext. Intercostals actually move up AND outwards.
    Also, in forced inspiration (when you take a breath on purpose or are breathing hard), serratus anterior becomes involved as well as the sternocleomastoid, Scalene muscles and the laryngeal/pharyngeal muscles. These are not used at rest!
    In forced expiration, the abdominal muscles come into play (int./ext. obliques, transversus abdominus and rectus abdominus (‘Six-pack’ muscles).
    At rest, expiration is passive and occurs due to elastic recoil.

  11. scottseptember1992

    @InteractiveBiology

    This is a wonderfully thorough video. The mentioning of “Boyle’s Law” (which describes the INVERSE relationship between Pressure and Volume, like popping a boil) would further clarify the ventilation mechanism. To integrate this to the NS, the Central NS’s Brain Stem sending signals the Peripheral Nervous System’s Motor System’s efferent (going away from CNS) neurons towards the diaphragm and intercostal muscles and causing them to contract is how this is all “regulated.”

  12. scottseptember1992

    @InteractiveBiology

    This is a wonderfully thorough video. The mentioning of “Boyle’s Law” (which describes the INVERSE relationship between Pressure and Volume, like popping a boil) would further clarify the ventilation mechanism. To integrate this to the NS, the Central NS’s Brain Stem sending signals the Peripheral Nervous System’s Motor System’s efferent (going away from CNS) neurons towards the diaphragm and intercostal muscles and causing them to contract is how this is all “regulated.”

  13. Mallory Richards

    This was really useful and helpful. I wish you had a video of ventilation-perfusion coupling. I have never watched a video from you that I don’t understand, and ventilation-perfusion coupling is hard.

  14. butabobotabu

    Your videos are really helpful. I always look for any videos that is related to the topic I work on before I start reading my lab manual.

  15. butabobotabu

    Also, could you please go into a little more details about how the decreasing pressure in the pleural cavity can affect the pressure inside the pulmonary cavity? Thanks a lot.

  16. Anna Craft O'Neal

    just a minor clarification, though I LOVE your videos, keep up the good work! During expiration, the pleural cavity pressure is still LESS than the pressure in the lungs (intrapulmonary pressure). During inspiration, it is the relative pressure of pleural to pulmonary that causes the influx of air as well as the relative difference of intrapulmonary to atmospheric (greater, at least -1mmHg), pulling air into the lungs. Air flows down gradient until Ppul = Patm. The pressure always wants to be =

  17. Chris H

    Very useful, thank you. Despite understanding Boyle’s law, I was having a hard time orienting myself on the movement of the diaphragm, intercostals, and lungs. Awesome job.

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