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Current time:0:00Total duration:11:10

Video transcript

all members of the kingdom Animalia need oxygen to make energy oxygen is compulsory without oxygen we die but as you know the byproduct of the process that keeps us all alive cellular respiration is carbon dioxide or co2 and it doesn't do our bodies a bit of good so not only do we need to take in the oxygen we also got to get rid of the co2 and that's why we have the respiratory and circulatory systems to bring in oxygen from the air with our lungs circulated to all of our cells with our heart and arteries and collect the co2 that we don't need with our veins and dispose of it with the lungs when we exhale now when you think of the respiratory system the first thing that you probably think of is the lungs but some animals can take in oxygen without lungs by a process called simple diffusion which allows gases to move into and pass through wet membranes for instance arthropods have little pores all over their bodies that just sort of let oxygen wander into their body where it's absorbed by special respiratory structures amphibians can take in oxygen through their skin although they also have other lungs or gills to help them respire because getting all your oxygen by way of diffusion takes freaking forever so what do we have to have these stupid lung things instead of just using simple diffusion well a couple of reasons for starter the bigger the animal the more oxygen it needs and a lot of mammals are pretty big so we have to actively force air into our lungs in order to get enough oxygen to run our bodies also mammals and birds are warm-blooded which means that they have to regulate their body temperatures and that takes many many calories and burning those calories requires lots of oxygen finally in order for oxygen to pass through a membrane the membrane has to be wet so for a newt to take oxygen and through its skin the skin has to be moist all the time which you know for a newt isn't a big deal but you know I don't particularly want to be constantly moist do you fish need oxygen too of course but they absorb oxygen that's already dissolved in the water through their gills if you've ever seen a fish Gill you'll remember that they're just sort of bunch of filaments tissue layered together the skilled tissue extracts dissolved oxygen and excretes the carbon dioxide still there are some fish that have lungs like lung fish which we call lung fish because they have lungs and that's actually where lungs first appeared in the animal kingdom all animals from reptiles on up respire with lungs deep in their bodies basically right behind the heart so while it's more complex animals can't use diffusion to get oxygen directly our lungs can lungs are chock full of oxygen dissolving membranes that are kept moist with mucous moist with mucous another great band name the key to these bad boys is that lungs have a ton of surface area so they can absorb a lot of oxygen at once you wouldn't know from looking at them but human lungs contain about 75 square me years of oxygen dissolving membrane that's bigger than the roof of my house and the simple diffusion that your lungs use is pretty freakin simple you and I breathe oxygen in through our nose and mouth it passes down a pipe called your larynx which then splits off from your esophagus and turns into your trachea which then branches to form two bronchi one of which goes into each lung these bronchi branch off again forming narrower and narrower tubes called bronchioles these bronchioles eventually end in tiny sacs called alveoli each alveolus is about a fifth of a millimeter in diameter but each of us has about 300 million of them and this friends is where the magic happens alveoli are little bags of thin moist membranes and they're totally covered in tiny narrow blood carrying capillaries oxygen dissolves through the membrane and is absorbed by the blood in these capillaries which then goes off through the circulatory system to make cells all over your body happy and healthy but while the alveoli are handing over the oxygen the capillaries are switching it out for carbon dioxide that the circulatory system just picked up from all over the body so the alveoli and capillaries basically just swap one gas for another from there the alveoli takes that co2 and squeezes it out through the bronchioles the bronchi the trachea finally out of you nose and/or mouth so inhale for me once congratulations oxygen is now in your bloodstream now exhale wonderful the co2 has now left the building and you don't even have to think about it so you could think about something more important like how many Cheetos you could realistically fit into your mouth at the same time so now you're oh yeah that's great Hank but how the lungs actually like work like how do they do the thing where they do where they get moved to come in and out and stuff well eloquent question well asks lungs work like a pump but they don't actually have any muscles in them that caused them to contract and expand for that we have this big flat layer of muscles that sits right underneath the lungs called the thoracic diaphragm at the end of an exhalation your diaphragm is relaxed so picture an arc pushing up on the bottom of your lungs and crowding them out so that they don't have very much volume but when you breathe in the diaphragm contracts and flattens out allowing the lungs to open up and as we know from physics as the volume of a container grows larger the pressure inside it goes down and the fluids including air always flow down there pressure gradient from high pressure to low pressure so as the pressure in our lungs goes down air flows into them when they die from real axis the pressure inside the lungs becomes higher than the air outside and the deoxygenated air rushes out and that is breathing now just so happens that the circulatory system works on a pumping mechanism just like the respiratory system except instead of moving air into and out of the lungs it moves blood into and out of the lungs the circulatory system moves oxygenated blood out of the lungs to the places in your body that needs it and then brings the deoxygenated blood back to your lungs and maybe you're thinking well what about the heart isn't the heart the whole point of the circulatory system will settle down I'm going to explain we're used to talking about the heart as the head honcho of the circulatory system and yeah you would be in serious trouble if you didn't have a heart but the hearts job is to basically power the circulatory system move the blood all around your body and get it back to the lungs so that it can pick up more oxygen and get rid of the co2 as a result the circulatory system of mammals essentially makes a figure eight oxygenated blood is pumped from the heart to the rest of the body and then when it makes its way back to the heart again it's then pumped on a shorter circuit to the lungs to pick up more oxygen and unload co2 before it goes back to the heart and starts the whole cycle over again so even though the heart does all the heavy lifting in the circulatory system the lungs are the home base for the red blood cells the postal workers that carry the oxygen in the co2 now the way that your circulatory system moves the blood around is pretty nifty remember when I was talking about air moving from high pressure to low pressure well so does blood a four chambered heart which is just one big honkin beast of muscle is set up so that one chamber the left ventricle has very high pressure in fact the reason it seems like the heart is situated a little bit to the left of center is because the left ventricle is so freakin enormous and muscley it has to be that way in order to keep the pressure high enough that the oxygenated blood will get out of there from the left ventricle the blood moves through the aorta a giant tube and then through the arteries and blood vessels that carry the blood away from the heart to the rest of the body arteries are muscular and thick-walled to maintain high pressure as the blood travels along as arteries branch off to go to different places they form smaller arterioles and finally the very little capillary beds which through their huge surface area facilitate the delivery of oxygen to all of the cells in the body that need it the capillary beds are also where the blood picks up co2 so from there the blood keeps moving down the pressure gradient through a series of veins these do the opposite of what the arteries did instead of splitting off from each other to become smaller and smaller little ones flow together to make bigger and bigger veins to carry the deoxygenated blood back to the heart the big difference between most veins and most arteries is that instead of being thick walled and squeezy veins have thinner walls and have valves that keep the blood from flowing backwards which would be bad this is necessary because the pressure in the circulatory system keeps dropping lower and lower until the blood flows into two major veins the first is the inferior vena cava which one's pretty much down the center of the body and handles blood coming from the lower part of your body and the second is the superior vena cava which sits on top of the heart and collects the blood from the upper body together they run into the right atrium of the heart which is the point of the lowest pressure in the circulatory system so all this deoxygenated blood is now back in the heart and it needs to stop up some more oxygen so it flows into the right ventricle and then into the pulmonary artery now arteries remember flow away from the heart even though in this case it contains the oxygenated blood and pulmonary means of the lungs so you know that this is the path to the lungs after the blood makes its way to the alveoli and picks up some fresh oxygen it flows to the pulmonary vein remember it's a vein because it's flowing to the heart even though it contains oxygenated blood and from there it enters the heart again where it flows into the left atrium and then into the left ventricle where it does the whole body circuit again and again again and again and that is the way that we work our hearts are really efficient and awesome and they have to be because we're endo therms or warm-blooded meaning that we maintain a steady internal temperature having an endothermic metabolism is really great because us vulnerable to fluctuations in external temperature than ectotherms or cold-blooded animals also the enzyme do all the work in our bodies operate over a very narrow range of temperatures in humans that ranges between 36 and 37 degrees Celsius the trade-off is that endotherms need to eat constantly to maintain our high metabolisms and also create heat and for that we need a lot of oxygen hence the amazing efficient four chambered heart and our gigantic frakkin lungs Fecteau therms on the other hand have slow metabolisms and don't need as much in the way of food a snake is totally pumped if it gets a meal once a month so since ectotherms aren't doing much in the way of metabolizing they don't need much in the way of oxygen so their circulatory systems can be you know a little bit janky and inefficient it's still cool remember back when we were tracking the development of chordates one of the signs of complexity was the number of chambers in an animal's heart visually have two chambers one ventricle and one atrium the blood gets oxygenated as it moves through the gills and then carries oxygen through the rest of the body back to the heart where it's moved through the gills again but reptiles and amphibians have three chambered hearts they've got two atria but only one ventricle what that means is that not all of the blood gets oxygenated every time it makes a full pass around the body so oxygenated blood gets pumped through the body and mixed up with the little deoxygenated blood not super efficient but again doesn't really have to be so there you have it the how and why behind how oxygen gets to all the places it needs to be the question is what powers the diaphragm what powers the heart where does that energy come from well it comes from the digestive system and that's what we're going to be talking about next time
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