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Respiratory System

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

The intake of oxygen into the lungs and producing carbon dioxide in return is the main function of the respiratory system. The respiratory system includes airways, lungs and respiratory muscles. When oxygen is breathed in, it enters the circulatory system through the lungs by the process of diffusion.

The respiratory system is designed to help exchange gases, oxygen, carbon dioxide with the environment and your blood. Now red blood cells have in them a special protein called hemoglobin that can bind to oxygen and carry it now that hemoglobin can also help the red blood cells transport carbon dioxide. Carbon dioxide can also be transported in the blood in the form of bicarbonate ion and that's done through the help of an enzyme called Carbonic anhydrase and what it does it combines carbon dioxide gas with water from the blood plasma to form carbonic acid which then disassociates because its a acid and gives off this H+ion forming bicarbonate ion. The nice thing about this is it helps buffer the blood to prevent any other pH changes.

Now, how do we do it? Well we use lungs. Other creatures on this planet use their skin to exchange gases some use gills obviously like fish, insects a lot of them have these little tubes running through their body to help gases get into their bodies but again like I said we use lungs just like birds and many other vertebrate land animals. Now the reason that we have lungs instead of using our skin or gills is that to exchange gases you need to be able to dissolve the oxygen and carbon dioxide which means you need to have that organ of respiration to be wet so by having lungs which are inside our body we can retain water since we're on land which tend to be a lot drier than water. We also need to warm the air so that it doesn't disturb the internal temperatures so let's take a quick look over here and see how is this accomplished?

Now this begins with this portion right here, above that we have our nasal cavity when you inhale air your nose hairs which some of us have more than others, jealous, they help filter out larger particles, pollens things like that then the mucus also helps trap little bits of fungal spores bacteria and other things because you're trying to cleanse the air. Now you have blood vessels which some you discovered maybe when you're a little kid and you started digging around and those blood vessels are really close to the surface to help give heat to the air that's coming in and they exude water to help humidify the air. It then goes through the opening to your trachea the this long tube here called the glottis you have a little flap called the epiglottis epi means above that epiglottis closes the opening to the larynx or voice box which is at the top of the trachea.

The epiglottis closes in order for you to be able to swallow food and not have it go go down into your trachea and lungs so once the air goes through the glottis it enters the larynx or voice box. It then goes through the trachea and you can see there's these weird little rings over there, those are bands of cartilage that help keep it inflated so as the air goes down, it then branches into these tubes called bronchi. The bronchi or the branches here they go into smaller and smaller bronchi until finally get into these tiny little branches the final ends of the bronchi which are called bronchioles. Now we're in alveoli ducts at the end of each of these branches you'll have these clusters of little sacs, each sac is called an aveolus and an alveolus's job is to be as really thin simple sac and each alveolus or alveoli is the plural as you can see here these yellow sacs are surrounded by blood vessels and they're thin enough like oxygen gas and carbon dioxide gas can cross the membranes very quickly and easily and they're little bit moist not too much and you actually produce a special chemical that disrupts hydrogen bonding, and that keeps those sacs which don't have any real strong support from collapsing and sticking to each other like if your pants get wet they start sticking to your legs like that.

Now again I pointed out how the cartilage rings here prevent that kind of collapse but if you had cartilage helping hold up opening the alveoli you would have problems with them being too thick. Now these little red things here those are muscles and what those muscles do, they're smooth muscles or vascular muscles and they can open and close to increase or decrease the amount of air that you are inhaling and exhaling every moment. Now let's take a look at how inhalation and exhalation works. The breathing is controlled by the brain stem. In there you have special neurons sitting at the base of your brain that are detecting data coming in from sensory receptors that are detecting changes in pH or carbon dioxide concentration. Now a lot of time people think while I breathe to get in oxygen that's why you want to breathe but you're actually triggering when to inhale and exhale based on the build up of pH sorry of carbon dioxide the more carbon dioxide you have the more acidic your blood and that depresses the pH so when the pH gets too low too acidic, that signals your body time to exhale and get that carbon dioxide out and suck in some fresh air alright? Now what this does the carbon, the brain stem sends signals to the diaphragm muscle which sits at the base of your chest right above your abdominal region and it also helps control the ribcage muscles.

Let's take a look at this. What a lot of people don't get is that when you inhale, what you're doing is you're contracting that diaphragm that's why your stomach sticks out when you inhale because this diaphragm muscle here is pushing down on the abdomen as you can see in this diagram here shaving your guts out because there's no other space to go that helps expand the space of the chest now your ribcage can move a little bit so you have muscles on the in on the outside of the ribcage help pull it up and that helps increase the space of your chest cavity by increasing the space that drops the pressure compared to the outside so air rushes in from the higher pressure outside then when I want to breathe out which you don't think about is that most of the action of exhaling or expiration as physiologists like to call, expiration happens mainly by relaxing, you relax that diaphragm muscle and then the muscles that keep your guts from toppling all over the place they help push that diaphragm back up, your chest starts to relax now you can help this along by tightening to squish that diaphragm up even faster you've also got muscles on the inside of your ribcage that can pull the ribcage down to help increase the pressure in your lungs squirting the air out so you just cycle back and forth between these two and that's how we breathe, so I hope that I helped inspire you to breathe some of the stuff in and learn more about the respiratory system.