Respiratory Structure & Function

Alright guys, in this lesson we’re going to talk about the general structure and function of the respiratory system.

Before we look at specifics, I want to talk about some general terminology that you will need to know as you’re going through these respiratory lessons. We are going to use this terminology a lot so I want to make sure that you understand what it is that we’re talking about. First, is respiration. Anytime you see the word respiration I want you to think gas exchange. So there are three types of respiration. External respiration occurs in the lungs. This is when our bodies are exchanging oxygen and carbon dioxide with the outside world. So we breathe in the oxygen and breathe out the carbon dioxide. That exchange process that occurs in the lungs is called external respiration, and we will talk about it a little bit more in just a minute. Internal respiration is the exchange of gases within the tissues. So this time we are taking the oxygen to the tissues to drop it off and we’re picking up carbon dioxide from the tissues to take it back to the lungs to be exhaled. So that exchange of oxygen for carbon dioxide in the tissues is called internal respiration. And then we have cell respiration. Cell respiration still involves seeing oxygen and carbon dioxide switch, but instead what’s happening is the cells are using the oxygen and then making carbon dioxide during their metabolic processes. All of this is one big cycle. We bring in oxygen through our lungs with external respiration, we take that oxygen to the tissues in internal respiration, then the cells use that oxygen in cell respiration. During that process, our cells make carbon dioxide, then we exchange that Carbon dioxide back into the blood and take it to the lungs where external respiration helps to get the carbon dioxide out of our bodies.

Lastly let’s define the difference between inspiration and expiration. Inspiration or inhalation is the process of pulling air into the lungs so that all of the rest of these processes can happen. Expiration or exhalation is forcing the air out of the lungs and back out to the external environment. So basically, breathing in, and breathing out. Make sure that you check out the breathing movements lesson to understand how we do that.

So let’s talk about the location of the respiratory system. We have both an upper respiratory tract and a lower respiratory tract. So, in the head and neck we see the upper respiratory tract. We have the oral and nasal passageways that lead back to the pharynx, which is the back of the throat. Then that leads into the trachea, which starts the lower respiratory tract. so, as the air comes in nasal passages against humidified filtered and mixed within the nostril then comes back through the nasopharynx oropharynx and laryngopharynx before it gets to the lower respiratory tract. You’ll notice this tube back here is the esophagus. There is a small piece of tissue here called the epiglottis that will cover the trachea when we swallow to make sure that if food goes down the right tube. We all know how it feels when the food doesn’t go down the right tube, right!?

Now, we will look at the lower respiratory tract in more detail in just a second, but what I want you to know is that the whole thoracic cavity is also involved in respiratory function. So the walls of the thoracic cavity are made up of the rib cage and the intercostal muscles, and the floor of the thoracic cavity is made of the diaphragm which is this red muscle that you see here. It is skeletal muscle that had innervations from the phrenic nerve. A fun fact here is that it is a skeletal muscle, therefore it is voluntary. However, the nerve signals sent from the phrenic nerve telling us to breathe are not always voluntary. Which is actually a good thing – that’s how we keep breathing when we’re asleep and not thinking about it! Again, check out the breathing movements lesson to see more on how these muscles get involved.

So, now let’s look at the lower respiratory tract! We saw how the pharynx brings the air down to the trachea, right? Before it gets into the trachea it has to go through the larynx or the voice box. The larynx is made up of the thyroid and cricoid cartilage. Just inside the larynx is where we find our vocal cords. Once the air passes pasta lyrics it enters the trachea. all of the air passages from here down are made up of smooth muscle. The trachea also contains c-shaped cartilage rings to help the trachea keep its shape and stay open at all times. So, when I say c-shaped that means it has a little opening on the posterior side that allows for a little bit of flexibility. the trachea then splits off into the left and right primary bronchi. bees have the same exact structure at the trachea they are just a little bit smaller. Then the primary bronchi split into the secondary bronchi. Again, same structure, just smaller. On the left, there are two secondary bronchi for the two lobes. And, on the right, we have three secondary bronchi because we have 3 lobes. You can’t actually see the third one here. The secondary bronchi then split into smaller tertiary bronchi to reach the farther areas of the lungs and now instead of rings, the cartilage is only present in plates. It still gives it a little bit of stability, but it isn’t as rigid. From there the passages split into many tiny bronchioles, which then branch into the alveolar ducts. That’s where we find our alveoli in the alveolar sacs. As you can see here, the alveolar sacs are surrounded by blood vessels and that’s how gas exchange happens.

Now, we have a whole lesson on gas exchange in the respiratory system, but I just want to give you a quick overview. Remember each alveoli is surrounded by blood vessels. The deoxygenated blood comes in and releases the CO2 into the alveoli to be exhaled, and the oxygen diffuses into the blood to be taken out to the body – this is that external respiration we were talking about. Important things to know about the alveoli is that there’s a fluid on the internal surface called surfactant that helps to keep the alveoli open and keep them from collapsing. There are also macrophages, which are a type of white blood cell, inside the alveoli to help protect us from foreign particles in the air. Again, check out the gas exchange and alveoli lessons in the respiratory course to learn more details.
So, let’s recap. Make sure you know the terminology – external versus internal versus cellular respiration – they all involve exchange of O2 and CO2, just in different locations. And of course, remember inspiration and expiration is the process of breathing in and out. We find the respiratory system in the head, neck, and thoracic cavity. The air flows from the upper respiratory tract – the oral and nasal passages plus the pharynx – into the lower respiratory tract – the trachea, bronchi, bronchioles, and then the alveoli. This is where gas exchange occurs – that’s our external respiration. And remember that the alveoli are held open with surfactant and have macrophages to try to protect us from foreign particles in the air.

So that’s the basic structure and function of the respiratory system. Make sure you check out the images and resources attached to this lesson, as well as the lessons on breathing movements, breathing control, and the respiratory functions of blood. Now, go out and be your best selves today. And, as always, happy nursing!