22.1-3Understanding the Respiratory System

Okay, so this lecture is going to focus on the respiratory system, which is chapter 22 in your textbook. The first three sections of this chapter are very anatomy heavy. meaning it's more pertinent information for lab. So I've included in these slides just a basic overview of the first three sections and things that I expect you to know for the lecture exam. However, for lab, you may need to go back in and understand more information that's not included in these slides. So typically, I don't cover these in lecture just for time purposes. However, I'm just going to put together. a basic overview of sections one through three right now in this video. So we've already talked a lot about the circulatory system and now we're going to focus on the respiratory system. Even though these are two distinct systems, they are closely coupled because they're both working and involved in gas exchange. So if we're talking about the major functions of the respiratory system the major function is gas exchange, where we are going to pick up oxygen in our lungs and drop it off to the tissues in our blood via the cardiovascular system, but also to remove the carbon dioxide. that we picked up as a metabolic waste product from our body. Also functions in olfaction, which is our sense of smell and speech because our respiratory system is moving air. There are four processes involved in the process of respiration. The respiratory system is responsible for two of these processes, and our circulatory system is responsible for two other processes. So if we're talking about the two processes, the respiratory system is responsible for that is pulmonary ventilation, which is our actual breathing. So the movement of air into and out of our lungs. And then the second process would be exhalation. external respiration, where we're actually exchanging oxygen and carbon dioxide between the lungs and our blood. We have the circulatory system that is responsible for two, again, of the processes of respiration. One of the processes is transport. We use our blood. It's a fluid connective tissue in order to transport these gases between our lungs and virtually everywhere in our body. And then internal respiration. which is the actual exchange of these gases between the systemic blood vessels and our body tissues. I did go over or make another overview video, which is not slide relevant, just to kind of hit in on the main concepts from the first three sections. It's under the supplemental section of this exam module. So again, these are the four processes of respiration. two of which the respiratory system is responsible for, and two of which the cardiovascular system is responsible for. I would kind of make sure you understand the four different processes and what those actually mean. Okay, major organs. Again, we're not going into the anatomy portion of this because this is the lecture. However, you may need to go back and reference a couple of these first sections in lab in order for you to identify a lot of the different structures on these different organs. Okay, so major organs for our respiratory system are divided into two main groups based off of whether they belong to what's considered the upper. respiratory system or the lower respiratory system. If we're talking about the upper respiratory system, we're talking about it beginning with our nose and ending at our pharynx. Our lower respiratory system is going to begin with our larynx and end with our alveoli, which are just tiny air sacs in our lungs. Overall, you should understand the function of the upper respiratory system, which is different from the overall function of the lower respiratory system. So overall, our upper respiratory system, again, that would include include our nose, nasal cavity, paranasal sciences, as well as our pharynx. The function would be to help warm, humidify, and filter the incoming air. You do need to have an understanding, general understanding. understanding, nothing super specific of the description and basic function of the structures in the upper respiratory system, as well as the lower respiratory system. So just go in and recognize what the structures are, what their general function is, and general description of each one. I do want to go ahead and point out that the pharynx does have three subdivisions based off of the location. of the segment of the pharynx in our body. So directly behind our nasal cavity, we have the nasopharynx. That's the most superior portion of the pharynx. And then below it, we have the oropharynx, which lies behind our tongue, and then our laryngopharynx, which is actually going to connect to our larynx itself. Okay, lower respiratory system. Again, we're talking about the larynx, trachea, bronchi, lungs, and alveoli. We break the lower respiratory system up into two different zones. We have a respiratory zone and a conducting zone. The respiratory zone is the actual site of gas exchange, and our conducting zone is going to be the conduits. Basically, their sole function is to just transport the gas to and from exchange. sites. So our respiratory zone is actually going to consist of our respiratory bronchioles, alveolar ducts, and alveoli. Our conducting zone, we're talking about all the other respiratory structures of the lower respiratory system, and their function is going to be to help cleanse, warm, and humidify the air. Okay, these are basic structures that are involved in the lower respiratory system. And again, just a basic description, basic function. You don't need to know all the details. Like for example, the trachea, the C-shaped cartilages that are incomplete, things like that. That's more lab-based. Here, I just want you to understand what the contribution of each one of these structures are. So for example, if we're talking about the larynx, that does house our vocal cords. which we call our true vocal cords because we also have false vocal cords. Our true vocal cords are the ones that are responsible for voice production. So our voice box and voice production is the function of the larynx. And if we're talking about our trachea, that's also referred to sometimes as our windpipe. And then we also have our epiglottis, which we consider to be the guardian of our airways. So again, just general description, what the structures are, general function of these in the lower respiratory system. Going a little bit more into voice production, again, which is the responsibility of our larynx itself, which houses the true vocal cords, we're going to talk about speech. So speech involves basically the intermittent release of expired air, so during expiration, during the opening and closing of the glottis. If we're talking about the pitch of our voice, that's going to be determined by the length and the tension of the vocal cords that are housed in the larynx. The longer and thicker means that the deeper your voice is, or the pitch of your voice is actually going to be. Longer and thicker vocal cords. Loudness is going to be dependent upon the amount of force of the air. So for example, if we increase the force of the air. We're going to increase the vibration, which means we're going to increase the loudness. Something really important that's covered in the first three sections is the respiratory membrane. So we're going to talk more about this in this chapter. But for now, just kind of understand what is the respiratory membrane. The respiratory membrane is basically the alveolar wall. and its basement membrane and the capillary wall of the blood vessels where they're fused with their basement membrane. So we have the alveolar wall attached to the capillary wall and a basement membrane fusion sandwiched between the two. This is what we refer to as the blood air barrier. Really, really thin as we would expect because this is going to be one of the sites of gas exchange. And again, if we're talking about gas exchange of oxygen and carbon dioxide, this is always going to be via simple diffusion, meaning it doesn't require any energy. There's three major types of cells found in this respiratory membrane. One is type 1 alveolar cells. Then we also have type 2 alveolar cells. And then we have macrophages. So if we're talking about the type 1 alveolar cells, this is the primary cell type. And these are just simple squamous epithelial cells. We also have scattered among the type 1 alveolar cells, type 2 alveolar cells, and they're cuboidal if we're talking about their shape. They're really important because they are going to secrete something called surfactant. Surfactant is a detergent-like substance. that coats all of the alveolar surfaces. We'll talk more about surfactant function later in this lecture for chapter 22. So alveolar type 2 alveolar cells secrete surfactant, but they also secrete antimicrobial proteins. So these are really important when we're talking about RNA immunity. The third type of cell was our alveolar macrophages. These are also very, very important because they're able to break down bacteria, dust, and debris in order to help keep our alveolar surfaces as close to sterile as possible. And because our macrophages are constantly being exposed to the bacteria, dust, and debris, they're constantly dying trying to fight this battle. They're dying in such high quantities. that we actually lose about 2 million macrophages per hour. And what we do is when they die, we just carry them with the cilia that's in our throat and we actually just swallow them. And then they go through our digestive system that way and eventually excreted or broken down. Another thing, so those are three types of cells. Another important attribute of our respiratory membrane are the alveolar pores. which actually connect all the adjacent alveoli together. These are really important when we're talking about the air pressure within our lungs. You'll see in a little bit that pressure differences are what's going to influence the movement of the gases. So the movement of these gases through these alveolar pores is actually really important. They can also provide alternate routes in case we have some sort of blockage in an alveoli or if we have bronchial. collapse. So here's kind of an image. This right here would represent one alveolus. A good way to think about the difference between an alveoli and alveolar sac is the alveolar sac basically kind of represents a bunch of grapes. If you were to pick a bunch of grapes up, each individual grape in the bunch of grapes would represent an alveoli. And here we can see the different cells that we just talked about that make up that respiratory membrane. If we zoom in on the respiratory membrane, we can see that it's made up of the alveolar wall right here, along with the capillary wall right here, and their fusion at the basement membranes. Our three important cells are our type 1 alveolar cell, which is just a simple squamous epithelium. Then we can see inner... Dispersed within our simple squamous epithelium are type 1 cells. We see the type 2 alveolar cells that are really important because they're going to secrete something called surfactant as well as antimicrobial proteins. And then our third type of cell are macrophages. There's several of them dispersed throughout our alveolar sac who are just going to function to help get rid of any unwanted debris or bacteria or dust. and basically eliminate it so we can keep the alveoli a sterile place. So these slides are just some general anatomy. Again, you're going to have to know way more in lab, but just a general overview of the structure of our lungs. So we have two lungs. The two lungs are going to differ in both their size and their shape. The left lung is going to be smaller than the right lung because of the position of the heart. So our heart sits right here and we have what's called the cardiac notch. So this is our left lung. Again, it's the person or the patient's left, not yours. So the left lung is slightly smaller and has a different shape than if you notice from the right lung, which is over on this side. Another difference between the left and right lung is that the left lung has two lobes. It has a superior and an inferior lobe. So this is the superior lobe, this is the inferior lobe, and then it's separated by the oblique fissure. Our right lung is divided into three lobes, not two lobes. So we still have our superior lobe. And we still have our inferior lobe, but our third lobe is the one that's in the middle, which is our middle lobe. Because we have three different lobes, we don't just have one fissure separating it. Now we need two fissures to separate each lobe. So we have the horizontal fissure that's going to separate the superior middle lobe, and then the oblique fissure that's going to separate the middle lobe from the inferior lobe. So another thing I just want to point out. Position wise, the apex of the lung is going to be at the top, just deep to the clavicle. And then the base of the lung down here, which is the wider portion of the lung, is at the bottom and it's going to rest right on top of your diaphragm. So each of our lobes also contains bronchial pulmonary segments. I just want to also point out differences in this between the right and the left lung. So if we're talking about our right lung, it has 10 bronchopulmonary segments. And our left lung has anywhere between 8 and 10. It's variable sometimes, bronchopulmonary segments. Each segment, whether it's on the right side or the left side, is served by its own artery and its own vein. This is really important because pulmonary disease is often combined. to only one or a couple of these segments. So if you do have some sort of pulmonary disease, you can go in and remove one of the segments or the affected segments without damaging the neighboring segments or impairing the neighboring segments' blood supply. Okay, pulmonary circulation. We already talked about this a little bit when we talked about the cardiovascular system, but just as a refresher, our pulmonary arteries, these are going to be carrying low-level oxygenated blood from the heart to the lungs so that we can pick up oxygen there. Our pulmonary veins are going to be carrying the heavily oxygenated blood that's leaving our lungs back to the heart. And again, if we're talking about pulmonary circulation, which is inclusive of our pulmonary veins, this is a low pressure, high volume system. Bronchial circulation. So just like when we talked about our cardiovascular system, we had our systemic blood supply, and then we had our coronary circulation. Because we cannot... supply, even though the blood is being held in the heart, the heart muscle itself couldn't utilize the blood that it was holding. The heart itself had to have its own circulation, which was the coronary circulation. Well, same thing with our lungs. Even though our lungs have the blood vessels going through them for the gas exchange, the lungs themselves need their own circulation and their own blood celli. And that's going to be the bronchial circulation. So we have bronchial arteries, and these are going to provide oxygenated blood or heavily oxygenated blood to the lung tissue itself. This is the reverse of the pulmonary arteries, with the exception of the alveoli themselves. Our pulmonary veins, these are going to carry the blood back to the heart itself. If we're talking about nerve innervation of the lungs. Both of our autonomic divisions, the sympathetic and the parasympathetic divisions innervate our lungs. The nerves are going to enter through what's called the pulmonary plexus, which is on the root of the lung. What do they control or what do they cause based off of the innervation? Well, the parasympathetic fibers are going to cause bronchial constriction. And sympathetic is going to cause bronchodilation. Again, parasympathetics are rest and digest. Sympathetic is our fight or flight. So we want our bronchioles to be able to dilate to get in the max amount of airflow possible. All right, the pleurite. This should be a review from AMP1 where you talked about the CRS membrane. So just as a refresher. Pleurae is referring to the membranes that are associated with the lungs. Pericardium would be the membrane associated with the heart. Parietal and visceral are just the terms referring to which of the two membranes you're talking about. So visceral is always going to be the membrane that's actually covering the surface of the organ. Because we're talking about the visceral pleura specifically, we're talking about the membrane that's actually covering the lung surface itself. The parietal pleura, parietal is going to represent the cavity in which the organ is housed. And so if we're talking about the parietal pleura, we're talking about the membrane that's lining the thoracic cavity, which is holding our lungs. It's also going to be present on the superior face of the diaphragm, a little bit around the heart, and also between the lungs themselves. In between these two membranes, the parietal pleura and the visceral pleura, we have pleural fluid. within this cavity. And anytime you have fluid in a cavity, its typical function is to help with lubrication and service tension from the movement of the organ itself.

So I've included in these slides just a basic overview of the first three sections and things that I expect you to know for the lecture exam. However, for lab, you may need to go back in and understand more information that's not included in these slides. So typically, I don't cover these in lecture just for time purposes.

However, I'm just going to put together. a basic overview of sections one through three right now in this video. So we've already talked a lot about the circulatory system and now we're going to focus on the respiratory system.

Even though these are two distinct systems, they are closely coupled because they're both working and involved in gas exchange. So if we're talking about the major functions of the respiratory system the major function is gas exchange, where we are going to pick up oxygen in our lungs and drop it off to the tissues in our blood via the cardiovascular system, but also to remove the carbon dioxide. that we picked up as a metabolic waste product from our body.

Also functions in olfaction, which is our sense of smell and speech because our respiratory system is moving air. There are four processes involved in the process of respiration. The respiratory system is responsible for two of these processes, and our circulatory system is responsible for two other processes. So if we're talking about the two processes, the respiratory system is responsible for that is pulmonary ventilation, which is our actual breathing. So the movement of air into and out of our lungs.

And then the second process would be exhalation. external respiration, where we're actually exchanging oxygen and carbon dioxide between the lungs and our blood. We have the circulatory system that is responsible for two, again, of the processes of respiration. One of the processes is transport.

We use our blood. It's a fluid connective tissue in order to transport these gases between our lungs and virtually everywhere in our body. And then internal respiration. which is the actual exchange of these gases between the systemic blood vessels and our body tissues. I did go over or make another overview video, which is not slide relevant, just to kind of hit in on the main concepts from the first three sections.

It's under the supplemental section of this exam module. So again, these are the four processes of respiration. two of which the respiratory system is responsible for, and two of which the cardiovascular system is responsible for. I would kind of make sure you understand the four different processes and what those actually mean.

Okay, major organs. Again, we're not going into the anatomy portion of this because this is the lecture. However, you may need to go back and reference a couple of these first sections in lab in order for you to identify a lot of the different structures on these different organs.

Okay, so major organs for our respiratory system are divided into two main groups based off of whether they belong to what's considered the upper. respiratory system or the lower respiratory system. If we're talking about the upper respiratory system, we're talking about it beginning with our nose and ending at our pharynx. Our lower respiratory system is going to begin with our larynx and end with our alveoli, which are just tiny air sacs in our lungs. Overall, you should understand the function of the upper respiratory system, which is different from the overall function of the lower respiratory system.

So overall, our upper respiratory system, again, that would include include our nose, nasal cavity, paranasal sciences, as well as our pharynx. The function would be to help warm, humidify, and filter the incoming air. You do need to have an understanding, general understanding.

understanding, nothing super specific of the description and basic function of the structures in the upper respiratory system, as well as the lower respiratory system. So just go in and recognize what the structures are, what their general function is, and general description of each one. I do want to go ahead and point out that the pharynx does have three subdivisions based off of the location.

of the segment of the pharynx in our body. So directly behind our nasal cavity, we have the nasopharynx. That's the most superior portion of the pharynx. And then below it, we have the oropharynx, which lies behind our tongue, and then our laryngopharynx, which is actually going to connect to our larynx itself. Okay, lower respiratory system.

Again, we're talking about the larynx, trachea, bronchi, lungs, and alveoli. We break the lower respiratory system up into two different zones. We have a respiratory zone and a conducting zone.

The respiratory zone is the actual site of gas exchange, and our conducting zone is going to be the conduits. Basically, their sole function is to just transport the gas to and from exchange. sites.

So our respiratory zone is actually going to consist of our respiratory bronchioles, alveolar ducts, and alveoli. Our conducting zone, we're talking about all the other respiratory structures of the lower respiratory system, and their function is going to be to help cleanse, warm, and humidify the air. Okay, these are basic structures that are involved in the lower respiratory system. And again, just a basic description, basic function. You don't need to know all the details.

Like for example, the trachea, the C-shaped cartilages that are incomplete, things like that. That's more lab-based. Here, I just want you to understand what the contribution of each one of these structures are.

So for example, if we're talking about the larynx, that does house our vocal cords. which we call our true vocal cords because we also have false vocal cords. Our true vocal cords are the ones that are responsible for voice production.

So our voice box and voice production is the function of the larynx. And if we're talking about our trachea, that's also referred to sometimes as our windpipe. And then we also have our epiglottis, which we consider to be the guardian of our airways. So again, just general description, what the structures are, general function of these in the lower respiratory system.

Going a little bit more into voice production, again, which is the responsibility of our larynx itself, which houses the true vocal cords, we're going to talk about speech. So speech involves basically the intermittent release of expired air, so during expiration, during the opening and closing of the glottis. If we're talking about the pitch of our voice, that's going to be determined by the length and the tension of the vocal cords that are housed in the larynx. The longer and thicker means that the deeper your voice is, or the pitch of your voice is actually going to be. Longer and thicker vocal cords.

Loudness is going to be dependent upon the amount of force of the air. So for example, if we increase the force of the air. We're going to increase the vibration, which means we're going to increase the loudness. Something really important that's covered in the first three sections is the respiratory membrane.

So we're going to talk more about this in this chapter. But for now, just kind of understand what is the respiratory membrane. The respiratory membrane is basically the alveolar wall.

and its basement membrane and the capillary wall of the blood vessels where they're fused with their basement membrane. So we have the alveolar wall attached to the capillary wall and a basement membrane fusion sandwiched between the two. This is what we refer to as the blood air barrier.

Really, really thin as we would expect because this is going to be one of the sites of gas exchange. And again, if we're talking about gas exchange of oxygen and carbon dioxide, this is always going to be via simple diffusion, meaning it doesn't require any energy. There's three major types of cells found in this respiratory membrane.

One is type 1 alveolar cells. Then we also have type 2 alveolar cells. And then we have macrophages.

So if we're talking about the type 1 alveolar cells, this is the primary cell type. And these are just simple squamous epithelial cells. We also have scattered among the type 1 alveolar cells, type 2 alveolar cells, and they're cuboidal if we're talking about their shape. They're really important because they are going to secrete something called surfactant.

Surfactant is a detergent-like substance. that coats all of the alveolar surfaces. We'll talk more about surfactant function later in this lecture for chapter 22. So alveolar type 2 alveolar cells secrete surfactant, but they also secrete antimicrobial proteins.

So these are really important when we're talking about RNA immunity. The third type of cell was our alveolar macrophages. These are also very, very important because they're able to break down bacteria, dust, and debris in order to help keep our alveolar surfaces as close to sterile as possible.

And because our macrophages are constantly being exposed to the bacteria, dust, and debris, they're constantly dying trying to fight this battle. They're dying in such high quantities. that we actually lose about 2 million macrophages per hour. And what we do is when they die, we just carry them with the cilia that's in our throat and we actually just swallow them. And then they go through our digestive system that way and eventually excreted or broken down.

Another thing, so those are three types of cells. Another important attribute of our respiratory membrane are the alveolar pores. which actually connect all the adjacent alveoli together.

These are really important when we're talking about the air pressure within our lungs. You'll see in a little bit that pressure differences are what's going to influence the movement of the gases. So the movement of these gases through these alveolar pores is actually really important.

They can also provide alternate routes in case we have some sort of blockage in an alveoli or if we have bronchial. collapse. So here's kind of an image. This right here would represent one alveolus.

A good way to think about the difference between an alveoli and alveolar sac is the alveolar sac basically kind of represents a bunch of grapes. If you were to pick a bunch of grapes up, each individual grape in the bunch of grapes would represent an alveoli. And here we can see the different cells that we just talked about that make up that respiratory membrane.

If we zoom in on the respiratory membrane, we can see that it's made up of the alveolar wall right here, along with the capillary wall right here, and their fusion at the basement membranes. Our three important cells are our type 1 alveolar cell, which is just a simple squamous epithelium. Then we can see inner...

Dispersed within our simple squamous epithelium are type 1 cells. We see the type 2 alveolar cells that are really important because they're going to secrete something called surfactant as well as antimicrobial proteins. And then our third type of cell are macrophages.

There's several of them dispersed throughout our alveolar sac who are just going to function to help get rid of any unwanted debris or bacteria or dust. and basically eliminate it so we can keep the alveoli a sterile place. So these slides are just some general anatomy. Again, you're going to have to know way more in lab, but just a general overview of the structure of our lungs. So we have two lungs.

The two lungs are going to differ in both their size and their shape. The left lung is going to be smaller than the right lung because of the position of the heart. So our heart sits right here and we have what's called the cardiac notch. So this is our left lung.

Again, it's the person or the patient's left, not yours. So the left lung is slightly smaller and has a different shape than if you notice from the right lung, which is over on this side. Another difference between the left and right lung is that the left lung has two lobes.

It has a superior and an inferior lobe. So this is the superior lobe, this is the inferior lobe, and then it's separated by the oblique fissure. Our right lung is divided into three lobes, not two lobes.

So we still have our superior lobe. And we still have our inferior lobe, but our third lobe is the one that's in the middle, which is our middle lobe. Because we have three different lobes, we don't just have one fissure separating it. Now we need two fissures to separate each lobe. So we have the horizontal fissure that's going to separate the superior middle lobe, and then the oblique fissure that's going to separate the middle lobe from the inferior lobe.

So another thing I just want to point out. Position wise, the apex of the lung is going to be at the top, just deep to the clavicle. And then the base of the lung down here, which is the wider portion of the lung, is at the bottom and it's going to rest right on top of your diaphragm. So each of our lobes also contains bronchial pulmonary segments. I just want to also point out differences in this between the right and the left lung.

So if we're talking about our right lung, it has 10 bronchopulmonary segments. And our left lung has anywhere between 8 and 10. It's variable sometimes, bronchopulmonary segments. Each segment, whether it's on the right side or the left side, is served by its own artery and its own vein.

This is really important because pulmonary disease is often combined. to only one or a couple of these segments. So if you do have some sort of pulmonary disease, you can go in and remove one of the segments or the affected segments without damaging the neighboring segments or impairing the neighboring segments' blood supply. Okay, pulmonary circulation. We already talked about this a little bit when we talked about the cardiovascular system, but just as a refresher, our pulmonary arteries, these are going to be carrying low-level oxygenated blood from the heart to the lungs so that we can pick up oxygen there.

Our pulmonary veins are going to be carrying the heavily oxygenated blood that's leaving our lungs back to the heart. And again, if we're talking about pulmonary circulation, which is inclusive of our pulmonary veins, this is a low pressure, high volume system. Bronchial circulation. So just like when we talked about our cardiovascular system, we had our systemic blood supply, and then we had our coronary circulation.

Because we cannot... supply, even though the blood is being held in the heart, the heart muscle itself couldn't utilize the blood that it was holding. The heart itself had to have its own circulation, which was the coronary circulation.

Well, same thing with our lungs. Even though our lungs have the blood vessels going through them for the gas exchange, the lungs themselves need their own circulation and their own blood celli. And that's going to be the bronchial circulation. So we have bronchial arteries, and these are going to provide oxygenated blood or heavily oxygenated blood to the lung tissue itself.

This is the reverse of the pulmonary arteries, with the exception of the alveoli themselves. Our pulmonary veins, these are going to carry the blood back to the heart itself. If we're talking about nerve innervation of the lungs.

Both of our autonomic divisions, the sympathetic and the parasympathetic divisions innervate our lungs. The nerves are going to enter through what's called the pulmonary plexus, which is on the root of the lung. What do they control or what do they cause based off of the innervation?

Well, the parasympathetic fibers are going to cause bronchial constriction. And sympathetic is going to cause bronchodilation. Again, parasympathetics are rest and digest.

Sympathetic is our fight or flight. So we want our bronchioles to be able to dilate to get in the max amount of airflow possible. All right, the pleurite.

This should be a review from AMP1 where you talked about the CRS membrane. So just as a refresher. Pleurae is referring to the membranes that are associated with the lungs.

Pericardium would be the membrane associated with the heart. Parietal and visceral are just the terms referring to which of the two membranes you're talking about. So visceral is always going to be the membrane that's actually covering the surface of the organ.

Because we're talking about the visceral pleura specifically, we're talking about the membrane that's actually covering the lung surface itself. The parietal pleura, parietal is going to represent the cavity in which the organ is housed. And so if we're talking about the parietal pleura, we're talking about the membrane that's lining the thoracic cavity, which is holding our lungs. It's also going to be present on the superior face of the diaphragm, a little bit around the heart, and also between the lungs themselves. In between these two membranes, the parietal pleura and the visceral pleura, we have pleural fluid.

within this cavity. And anytime you have fluid in a cavity, its typical function is to help with lubrication and service tension from the movement of the organ itself.

Transcript for:22.1-3Understanding the Respiratory System

Transcript for:
22.1-3Understanding the Respiratory System