June 29, 2011

062 Pressure Changes during Breathing

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.

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