Introduction to Lung Physiology: Study with Video Lessons, Practice Problems & Examples

The respiratory system functions through two main processes: ventilation and respiration. Ventilation involves the movement of air in and out of the lungs, facilitated by the diaphragm's contraction during inspiration and its relaxation during expiration. Respiration encompasses external respiration, the gas exchange in the alveoli, and internal respiration, where oxygen and carbon dioxide are exchanged between blood and tissues. Hemoglobin plays a crucial role in transporting these gases. Understanding these processes is essential for grasping how oxygen reaches tissues and carbon dioxide is expelled from the body.

Ventilation and Respiration

Alright, folks. As we dive into the physiology of the respiratory system, we're going to be talking a lot about two things: ventilation and respiration. So we're going to break these things up here. Now remember, our real goal here is to get oxygen to the tissues of our body and to get carbon dioxide out of those tissues and back into the air. So that's sort of what our respiratory system is doing. And when we think of that process, altogether sort of breathing, we can take that and break it up into two components. The first is going to be ventilation, and ventilation is the moving of the air in and out of our lungs, getting the air in and out of our body. And the second one is going to be respiration. And respiration is getting that oxygen, that oxygen, O₂, and CO₂, the carbon dioxide, getting that in and out of the blood. Alright. So let's break these things down separately. Let's go through ventilation first. So we said that is the movement of air in and out of the lungs. Well, there are two basic processes to that. We have inspiration. And inspiration, that's your normal inhale. That's your breathing in, and this moves air into the lungs. Now inspiration, we're going to say here, uses muscular force. And our major muscle of breathing here, our diaphragm, we have this illustrated. So we have our anatomical model. We can see the respiratory system. And importantly, we see the diaphragm pulling downwards. It contracts, pulls downwards, makes more space in that thoracic cavity, which pulls air into the lungs. So that uses force. The muscles of the diaphragm are using energy to pull downwards in that case. Now in contrast, we have expiration. Expiration, well, that's our breathing out. That's our exhale, we'll say, and this moves air out of our lungs. And this is a little counterintuitive to some people, a lot of times. This normally just involves muscular relaxation. So we use force to bring air into our lungs, but then to breathe out, that diaphragm is going to go back up. But it's just everything sort of recoiling to its natural space. So sort of your natural tendency, if you just relax, you're going to expire, you're going to exhale. Alright. Now what I've just described is what happens in what we call quiet breathing. And quiet breathing, there's a vocab word for that. We call it eupnea. So eupnea or quiet breathing, that's just that normal quiet breaths, restful breathing, the type of breathing that you do when you just don't think about breathing and you're not doing anything too strenuous. This is what we're going to use for most physiological measures. So as we go through this chapter, when you see volumes, numbers, unless stated otherwise, we're talking about that quiet, restful breathing. Now, obviously, we can breathe harder than that. And when we do that, we call it forced breathing. Forced breathing is deeper, harder breathing, either because you're doing something very strenuous or you're deliberately taking big breaths, something like that. Now in forced breathing, we are going to use muscles for inspiration just like in quiet breathing, but we're going to recruit more muscles to help us breathe in deeper. But we're also going to use muscles for expiration. So in forced breathing, we force air into our lungs, and we use muscular force to force the air out again. Alright. So now let's talk about respiration. So respiration, we've gotten the air into our lungs. Well, now how do we get it to the tissues? Well, there's going to be two steps to this. First, we have external respiration. This is going to be that exchange of oxygen and carbon dioxide between the air and the blood, and that happens in the alveoli. So we have this image of the alveoli drawn there. Now, some people sometimes get a little confused. External respiration, this is happening in my alveoli. My alveoli are in my chest. That seems kind of in my body. Why is it external? The way I think of it, it's the exchange between the blood and the external air. You bring this external air in through ventilation, and this exchange of gases happens in the alveoli, external respiration. Alright. Where we really want to get those gases to and from though is the tissues, and that is internal respiration. So the blood leaves the alveoli, takes it to the tissues, and then we have this exchange between the blood and tissues. And to illustrate this, we have this drawing of, sort of, simple columnar epithelium here. So that's where that oxygen is going to pop out of the blood, go into the tissues, excess carbon dioxide waste is going to come out of the tissues in the blood, so it can be carried back to the alveoli for external respiration. Alright. Just a quick note, that word respiration, sometimes people get a little confused. We also have cellular respiration. Cellular respiration is breaking down molecules like sugar to make ATP. We use oxygen for that, and that produces carbon dioxide. That is something different. Now, obviously, it's related. That's where this oxygen is going. That's where this carbon dioxide is coming from. But respiration in the respiratory system is something very different than cellular respiration; the using and production of these molecules in the making ATP from molecules like sugar. Alright. The final note that we just have here, in respiration, we have hemoglobin. Hemoglobin, you've learned about when you've learned about the blood, is this incredibly important molecule because when we exchange these gases we actually need a ton of oxygen. And it increases the amount of oxygen especially, but also CO₂ to a lesser extent, importantly oxygen though, that can be carried in the blood. Alright. So again, we want to get these molecules to and from the tissues, but there are two steps to do that. We need to get the air in and out of our lungs. That's ventilation. We need to get the molecules in and out of the blood. That's respiration. Alright. We're going to have a lot more on this going forward. It's going to be a grand old time. See you there.

Introduction to Lung Physiology Example 1

For this example, we need to remember the definitions that we just learned, and so we need to match the definitions to these four words: respiration, inspiration, expiration. Do you remember which one of those words refers to the movement of air out of the lungs? Well, that is going to be expiration. Expiration is the movement of air out of your lungs. The next one we have here is the exchange of gases with the blood. Do you remember which one that is? Alright, the exchange of gases with the blood. This is one that, for me, is always hard to remember that this is what's going on there, but that is respiration. Respiration, the movement of that carbon dioxide and oxygen specifically in and out of the blood. So, I'm going to put a on the line for number 2 there.

Next, we have movement of air into the lungs. Alright, which one of those words is the movement of air into the lungs? Well, that was inspiration. Inspiration right there, b. So I'm going to put b on this line here for number 3. And then finally, we have movement of air into and out of the lungs. That movement in and out together. What do we call that? Well, there's only one option left, but let's make sure it makes sense. Ventilation. That is what we call it. We ventilate our lungs by moving air in and out, so I'm going to put d here on the line for number 4. Alright. Those four words we're going to be using a lot going forward, so make sure you have them straight in your head.

The exchange of gases between blood and the air in the lungs is known as:

• A. Ventilation.
• B. Cellular Respiration.
• C. External Respiration.
• D. Internal Respiration.

Most physiological measures are taken during eupnea, or quiet breathing. This means that:

• A. Ventilation is a passive process that does not use muscular force.
• B. Muscular force is used for inspiration but not expiration.
• C. Muscular force is used for expiration but not inspiration.
• D. Muscular force is used for both inspiration and expiration.

Ventilation

We've broken up the functions of the respiratory system into ventilation, the movement of air in and out of the lungs, and respiration, the movement of those gases in and out of the blood. We're going to go through those separately and we're going to start with ventilation. So we want to introduce this now. Now again, here, we're not going to go into a lot of detail. We just want to set this up, so as we get into the details, you see how all this fits together. Alright. So ventilation, we are going to say, is performed by changing the volume of the thoracic cavity. The thoracic cavity, right, that space basically inside your rib cage. So to breathe, to ventilate your lungs, the main job that we're going to do is we're going to make that space inside your rib cage either bigger or smaller. And so we're going to say here that the lungs are really the only structure in that thoracic cavity that can change size significantly. There's other stuff in there, but as you change the size of the thoracic cavity, something has to fill up the more or less space that you're creating, and the lungs are really the only thing that can change size to do that. So we're going to do this in 2 ways. We can do inspiration. And for inspiration, right, we have that volume going up. So we have our anatomical model here, and for inspiration, that diaphragm pulls down, making that space inside the thoracic cavity bigger. And we're going to say there, when you do that, well, the thoracic cavity gets bigger. That makes the lungs get bigger, and so air flows into the lungs to fill up that extra space in the lungs. Alright. Now in the other way, we have expiration. And when you do expiration, well, that volume goes down. And to illustrate that, we have an anatomical model here and this diaphragm is recoiling and going back up, making that space inside the rib cage smaller. And we're going to say here, well, that smaller size, that forces the lun

Ventilation occurs when:

• A. Muscles cause the volume of the thoracic cavity to change.
• B. The gas molecules pass between air and the blood.
• C. Changes in pressure cause a change in the size of the thoracic cavity.
• D. The lungs contract and relax, altering the size of the thoracic cavity.

Here’s what students ask on this topic:

What is the difference between ventilation and respiration in lung physiology?

Ventilation and respiration are two distinct processes in lung physiology. Ventilation refers to the movement of air in and out of the lungs, primarily facilitated by the diaphragm. During inspiration, the diaphragm contracts and pulls downward, increasing the thoracic cavity's volume and drawing air into the lungs. During expiration, the diaphragm relaxes, reducing the thoracic cavity's volume and expelling air from the lungs. Respiration, on the other hand, involves the exchange of gases. External respiration occurs in the alveoli, where oxygen from the air is transferred to the blood, and carbon dioxide from the blood is expelled into the air. Internal respiration is the exchange of gases between the blood and body tissues. Hemoglobin in the blood plays a crucial role in transporting these gases.

How does the diaphragm contribute to the process of ventilation?

The diaphragm is a dome-shaped muscle located at the base of the lungs and plays a crucial role in ventilation. During inspiration, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity. This expansion creates a negative pressure that draws air into the lungs. During expiration, the diaphragm relaxes and moves upward, decreasing the thoracic cavity's volume and pushing air out of the lungs. This process is essential for the movement of air in and out of the lungs, facilitating the exchange of oxygen and carbon dioxide.

What is the role of hemoglobin in respiration?

Hemoglobin is a protein found in red blood cells that plays a vital role in respiration by transporting oxygen and carbon dioxide. Each hemoglobin molecule can bind up to four oxygen molecules, allowing it to carry a significant amount of oxygen from the lungs to the tissues. In the tissues, hemoglobin releases oxygen and picks up carbon dioxide, a waste product of cellular respiration. The carbon dioxide is then transported back to the lungs, where it is expelled during expiration. Hemoglobin's ability to bind and release these gases efficiently is crucial for maintaining proper oxygen and carbon dioxide levels in the body.

What is the difference between external and internal respiration?

External and internal respiration are two phases of the gas exchange process. External respiration occurs in the alveoli of the lungs, where oxygen from the inhaled air diffuses into the blood, and carbon dioxide from the blood diffuses into the alveoli to be exhaled. This process is facilitated by the thin walls of the alveoli and the extensive capillary network surrounding them. Internal respiration, on the other hand, takes place at the cellular level within body tissues. Oxygen carried by hemoglobin in the blood is released into the tissues, and carbon dioxide produced by cellular metabolism diffuses into the blood to be transported back to the lungs. Both processes are essential for maintaining the body's oxygen and carbon dioxide balance.

What is the significance of the alveoli in the respiratory system?

The alveoli are tiny, balloon-like structures in the lungs that play a critical role in the respiratory system. They are the primary sites for gas exchange, where oxygen from the inhaled air diffuses into the blood, and carbon dioxide from the blood diffuses into the alveoli to be exhaled. The alveoli have thin walls and are surrounded by a dense network of capillaries, which facilitates efficient gas exchange. The large surface area of the alveoli, combined with their thin walls, allows for a high rate of oxygen and carbon dioxide diffusion, making them essential for maintaining proper oxygen and carbon dioxide levels in the body.