A User's Guide to the Human Body

i know piloting this big complicated collection of cells and tissues we each inhabit can be daunting but over the years we here at scishow have compiled quite a few tips and tricks enough to put together a user's guide to the human body well an actual user's guide would probably fill several textbooks so maybe this is more of a quick start guide crash course if you like either way here's what we can tell you first you may be aware that you need to maintain your human body at a consistent temperature 37 degrees celsius to be exact give or take a few but why is our body's temperature requirement so demanding and so consistent from person to person part of the reason might be fending off fungal infections here's me with much much shorter hair to explain if you pulled out a thermometer and took your temperature right now you'd probably get a reading around 37 degrees celsius that number may vary a little from day to day or even hour to hour but overall your body temperature is pretty consistent if you get too hot your blood vessels will expand and you'll sweat to cool down if you get too cold your blood vessels will contract and you'll shiver to warm up and if you stray more than a couple degrees in either direction like with really bad fever or in freezing weather your proteins and cells will stop working and you could die so why is 37 degrees the magic number why not 35 or 40. well one major theory suggests it's all about keeping out fungus scientists have found that certain animals like reptiles and amphibians get a lot of different fungal diseases and they're all ectotherms they depend on external heat sources to stay warm specifically they get way more fungal infections than their endotherm counterparts like mammals which generate body heat internally researchers from yeshiva university wanted to find out why they tested the heat tolerance of different species of fungus starting at a temperature of 30 degrees celsius they found that every one degree increase in temperature caused a six percent decrease in the number of fungal species that are able to infect an animal host so if you're a frog depending on sunlight to warm you up you've got to worry about tens of thousands of fungal species that can infect you and cause life-threatening disease but if you're a mammal hovering around 37 degrees only a few hundred fungi can survive long enough to mess with you in other words when it comes to the risk of fungal infection it really helps to be hot then again you don't want to be too hot after all it takes a whole lot of energy to maintain a high body temperature you don't want to spend all of your time finding food and eating it you want to find a perfect balance and guess what when these researchers ran some mathematical models weighing the benefits of protecting against fungi versus the cost of extra food consumption they calculated an ideal body temperature of 36.7 degrees celsius which is right around our toasty 37 degrees in fact these scientists even think that maintaining this warm body temperature helped mammals thrive as the dinosaurs went extinct even though it's energy intensive it's possible early mammals started to beat out reptiles simply because we were more resistant to fungus so i guess our hotness helped us survive i stand by that line we're hot and that's a good thing now you also need to put your human body into rest mode periodically to maintain optimal performance yes i know it sounds strange but stay with me we really do need to sleep sometimes the question is whether it's possible to spend too long in this powered down state research suggests that might be the case here's olivia to explain how when people talk about having too much of a good thing they usually mean over-indulging in something like cake or fast food things you probably enjoy even if they aren't very good for you but what about something that's objectively important to your health and well-being like sleep well it turns out that you can get too much of that too most people need seven to nine hours of sleep and over sleeping is connected to health problems like depression heart disease and diabetes a 2014 study of 894 pairs of twins for example showed that the genetic risk of depression was higher in subjects who got less than seven hours of sleep or nine or more hours of sleep every night meaning people who overslept or under slept were more likely to be depressed because of genetic factors as opposed to environmental ones and according to a study on the sleep habits of 400 000 taiwanese adults the risk of coronary heart disease is about the same in people who sleep less than four hours a night as it is in those who sleep more than eight hours a night subjects who under slept had a 35 higher risk of heart disease and people who overslept had a 34 increase another study published in 2009 followed 276 subjects for six years and found that people who slept either less than 7 hours or more than 8 hours were at least twice as likely to develop type 2 diabetes or trouble tolerating glucose and there's more a 2013 study of about 54 000 adults over the age of 44 found links between too much sleep and increased rates of heart disease diabetes obesity stroke and mental health issues in fact the rates of coronary heart disease diabetes and stroke were even higher in people who overslept than in those who slept too little so the links are there sleep correlates with all kinds of health problems but it's hard to say whether too much sleep actually causes these issues it's totally possible that oversleeping is actually a symptom of things like depression or heart disease or that there's some other connection either way consistently sleeping too much might be a bad sign good to know oversleeping might be a sign it's time for some maintenance by a physician it's also possible that at times your human body might request maintenance in the form of input of specific food stuffs cravings i mean sometimes you just get a hankering for taco bell and nothing but a cheesy gordita crunch with extra jalapeno sauce will make it go away here's me again to explain why that happens starts off quiet a gentle whisper in your ear you're working hard so you push the thought away but soon it comes back louder and more urgent you start thinking about the bar in your backpack how delicious it would taste and pretty soon it's all you can think about as your brain chants louder and louder like chocolate until you cave in and give it exactly what it wants sound familiar you're not alone maybe it was bacon or pizza or a chai latte but nearly everyone has felt food cravings at some point but why and is this unshakable desire for a chocolate bar my body's way of telling me i need more magnesium well before we can talk about cravings let's look at hunger actual physiological hunger is how your body tells your brain it needs a resupply of calories it isn't about specific flavors it's about survival when your stomach is empty and your blood sugar levels are dropping your body starts secreting ghrelin otherwise known as the hunger hormone the ghrelin tells the hypothalamus in your brain that you need to eat and triggers a chain reaction that revs up your appetite and gets your digestive system ready to receive food and then once you've gobbled down enough food to stretch your stomach a bit the ghrelin tap turns off and you feel satiated for a while but if you've ever been tempted by the dessert menu even after a big meal you know that food cravings are different from straight-up hunger in some cases a food craving can be a sign that you need more of a specific nutrient if you're very low on salt for example you might crave potato chips or pretzels but if you need something more specific say magnesium there's no evidence that you'll start craving chocolate even though chocolate has magnesium in it often cravings are more about a psychological hunger than a physiological one and they can be wrapped up in emotions like stress and anxiety in the past we've talked about how humans tend to be drawn to fatty high carb foods in part because they're loaded with the energy we need to think and move and do stuff sir that's a physiological need but the pull toward junk food is often a psychological one as well eating a butter frosted cupcake or a bag of salty french fries releases an opioid typhoon that lights up the brain's pleasure center and makes us feel awesome at least for a while celery just doesn't have the same effect cravings are also tied to your brain's memory center which explains why you might also crave a food that isn't full of fat or sugar your brain could be tying that food to a happy memory or a feeling of reward and thinking about a memory associated with a food can make you crave that food another psychological cause of cravings can be a boring or restricted diet in studies where subjects had to drink only meal replacement shakes they ended up with a lot more cravings than usual especially for solid foods and this diet provided all the calories and nutrition that the subject's bodies technically needed so they probably didn't get those extra cravings because they were missing out on some nutrient pregnancy hormones on the other hand probably don't cause cravings pregnant women are often portrayed as having serious urges for things like pickles and ice cream but there isn't actually much evidence for a connection between those hormones and cravings instead these cravings probably have more to do with mood so if you're really jonesing for that chocolate it's probably just because your brain remembers that it feels good to eat it i mean is anyone here gonna deny that taco bell is delicious next you might be confused by some of the seemingly useless extra parts that your human body shipped with like your appendix except well the appendix was dismissed as pointless for years until researchers discovered the point here's stefan with more the appendix gets a bad rap you probably never even think about it unless it's the reason you're doubled over in abdominal pain and for the most part it gets written off as a useless organ left over from our evolutionary past but even though you can usually ignore it you've got to give your appendix some credit because it might not be as useless as you thought the appendix has evolved in mammals at least 29 times which is a pretty good sign that it does something and back in 2016 an international team of researchers set out to understand why it appears so many times they started by looking at what kinds of things animals with appendixes have in common but first they had to define what an appendix even is since the thing we call an appendix comes in all shapes and sizes across mammals as a starting point the researchers defined it as a section of tissue extending from the cecum the beginning of the large intestine they then used computer models to analyze data on hundreds of mammals they gathered information about their habitats and social behavior and of course whether or not they had an appendix and they concluded two things the first was that the appendix has evolved more times than it's been lost so it must have some kind of evolutionary advantage and second after finding high concentrations of lymph tissue which protects the body against foreign invaders they concluded that the appendix is involved in immunity across mammals and that seems to be the case for humans as well within the inner layers of the appendix we find all kinds of densely packed immune cells including t and b cells and natural killer cells which are all important parts of your body's immune response but we also find a reservoir of good gut bacteria hanging out in there that's the same type of bacteria that line the insides of the intestine creating a protective barrier against invaders given its prime position just off the colon researchers think the appendix might dish out emergency rations of gut bacteria in times of crisis like during cases of extreme diarrhea diarrhea can flush out your intestines but the impediments may be able to provide a fresh population of the gut bacteria that keeps your digestion on track they say you don't know what you have until it's gone and it's true one way to appreciate the immune function of the appendix is to see what happens when it comes out a study published in 2015 found that patients who contracted a particular bacterial infection called clostridium difficile were twice as likely to develop a severe infection if they didn't have an appendix that study alone doesn't prove that the appendix prevents infection but it does raise questions about whether or not surgeons should remove the appendix when they don't need to since that might actually cause trouble rather than prevent it that said appendicitis can be deadly so if your appendix needs to come out it's coming out but otherwise maybe we shouldn't be so quick to dismiss this organ that's usually just trying to be a pal that's sweet it's doing its best speaking of extra bits and bobs our human bodies also ship with considerable variation from unit to unit and in general these differences are great sometimes though there's even more going on than we realize like the fact that we have hundreds of blood groups beyond the four that we usually learn about once more let me explain what that means at some point like if you've donated blood you might have been asked about your blood type and even if you don't know what yours is you're probably aware that you could have a b a b or o blood and that your blood can be positive or negative but that's not the whole story because there are potentially millions of blood types out there there are so many possible blood types because of the way blood types are defined you see your blood type is defined by the antigens present in your blood antigens are anything that can elicit a response from your body's self-defense system though your immune system normally ignores the ones that belong to you and you can find antigens on cells throughout your body with different cells having different combinations of antigens the ones that matter for blood classification are found on the surfaces of your body's red blood cells simply put your particular blood type depends on which antigens are or aren't there like if you have a b blood that means you have both the a and b antigens in the blood group you could be just a or just b or if you're o you don't have either but those antigens are just two of over 600 blood antigens identified by the international society of blood transfusion and the list hasn't stopped growing yet many of these antigens fit into blood group systems like each of which is defined by a gene at a single site or by multiple genes that are closely related and all of us have these genes your type for a particular group depends on how your genes translate into the antigens that end up on the outside of your blood cells there are 36 blood group systems currently recognized so your full blood type if written out would include all 36 of these groups and the variants you have or don't have for all of those 600 plus antigens which is why we can say that there are millions of potential blood types of course there are only eight common ones and that's because many of these antigens are found in practically everyone while others are present in only a few individuals for example the sara antigen has only ever been seen in two families while 99.96 percent of people have the vel antigen and blood groups can get really complicated too just look at the rh blood group that's the group that gives you a positive or negative blood type like if you're a b positive the positive part generally means you have the rh antigen called rhd but to make things more confusing whether your blood is considered positive or negative may depend on how much of the antigen you have in your system since that can impact what sorts of antibodies your immune system makes to protect you and d is just one of over 60 known antigens in the rh group so positive or negative doesn't even begin to capture your overall rh blood type in fact one of the rarest blood types in the world occurs if you have none of the antigens in the rh group if you're one of the roughly 50 people with this blood type which is known as the rh null your body will reject the blood from practically anyone else and the rh group isn't the only blood group where having no antigens can be a matter of life or death another example is the diego group its antigens are proteins that help the lungs and kidneys perform essential functions like with the group there are two primary antigens a and b that determine a person's diego blood type but unlike the group where o or the lack of antigens is most common there has only been one documented case of someone lacking both of these key diego antigens sometimes though having no antigens can help you out for example one of the malarial parasites uses antigens in the duffy blood group to target and infiltrate cells so having no antigens from that group can make you more resistant to the disease but it also means there's a chance that your body will attack another person's blood if you're given a transfusion since the cells you receive could have duffy antigens on them that your body sees as foreign the good news is that despite all the potential blood types you could have for the most part the rh blood typing we're using does a pretty good job of matching people's blood with this system if you receive blood from someone with the same rh type there's a 99.8 chance your blood will be compatible with your donors for some reason your body's immune system doesn't go after every antigen equally so you don't usually need to know what version of every single known antigen you have and if you do want to be extra sure there are ways doctors can tell if you have a rare blood type for example they can screen for unexpected antibodies that could potentially target donated red blood cells or perform cross matching where your blood is mixed with the donors to see how the two react doing these two steps racks your safety margin up to 99.95 and if you do happen to have a rare blood type like rh null don't fret efforts like the international rare donor panel work hard to make sure you can get the blood you need no matter where in the world you are one person needing a transfusion had a rare blood type delivered from the uk to cameroon that's about 4 000 miles away so even if your blood is literally one in a million you can be pretty confident that you'll be able to find someone whose blood matches yours and finally it's important to realize that our bodies sometimes require the use of carefully designed chemicals to maintain optimal function i'm talking about medicine but the dose of these chemicals can vary a lot depending on the unit's age in other words you can't give the same amount of medication to a child as you do to an adult but how the dose varies might surprise you stefan can tell us more if you've ever strolled through a pharmacy in search of over-the-counter meds you might have noticed that lots of drugs have special children's formulas and you might think that's because smaller people need smaller doses but you'd be wrong because kids aren't just tiny adults in fact children sometimes need larger doses of medicine welcome to the weird science of alloma tree olmetry simply refers to the study of how physiology changes with size and it plays a big part in understanding how much medicine kids should get you might think bigger bodies would need larger doses of medicine since they have more of whatever tissue or cells the drug is targeting and there are a lot of medications that are prescribed based on a patient's weight what's sometimes referred to as a weight-based dose for instance an adult might be prescribed five milligrams of medicine for every kilogram they weigh but what's really weird is that this dose isn't constant throughout a person's lifetime you often can't take the dose per weight an adult would take and simply multiply it by the child's weight to figure out how much they should get and that's largely because a person's cells use less energy as their body grows in other words bigger people have lower mass-specific metabolic rates than smaller ones even at the cellular and subcellular level oxygen and calorie consumption is just slower in larger bodies not only that but it's a non-linear relationship so as bodies get smaller metabolism increases fast and that matters when it comes to medicines because it impacts how fast your body processes drugs generally speaking the faster the metabolism the faster you break down a drug and that means that even if you're small you might need to take more to have the amount you need stick around long enough for it to work let's consider acetaminophen which you might know is tylenol it's an over-the-counter drug that you can take to reduce pain and fevers the regular adult dose for acetaminophen is 650 milligrams so an adult weighing roughly 80 kilograms the average mass for adults in north america would generally take that amount every four to six hours as needed and if you'd never heard of velometry you might think a child one quarter that weight at 20 kilograms or so would get 162.5 milligrams but that's way too little the child will metabolize it super quickly so the drug won't really have a chance to be effective with junior strength tablets the recommended dose is actually 240 milligrams and for a 44 kilogram child the recommended amount is 640 milligrams that's basically the same as what's recommended for adults even though the child is about half the weight and if you calculate the weight-based doses for everyone the children actually take about two times as much and other drugs can be even more extreme the adult dose of oseltamivir which is an antiviral used to treat influenza infections is a hundred and fifty milligrams a day so a little under two milligrams per kilogram per day for our 80 kilogram adult but pediatric doses range from three to six milligrams per kilogram per day now as for why metabolic rate scales with mass in this strange non-linear way well physiologists don't know for sure but by looking at people and animals of all sizes they've come up with some good hypotheses the first and perhaps most obvious is that little bodies belong to individuals that are still growing and it takes more energy to build tissues than to maintain them so that's probably part of it but there has to be more going on because the allometric pattern holds across different sized adults too that's where the shapes of smaller and larger bodies might be coming into play because a smaller body has a larger surface area relative to its tiny volume it loses core heat faster and that means it needs to burn more energy and therefore run a higher metabolic rate to stay warm but even that still doesn't fully explain the allometric scaling of metabolic rate seen in nature because it only makes sense in so-called warm-blooded species like us that strictly regulate their internal temperature with the heat they produce and this metabolic rate scaling occurs in reptiles and other so-called cold-blooded species as well there may be another way that overall shape impacts all of this though which helps explain that some mathematical work suggests metabolic rates in large animals are limited by their internal plumbing see branching blood vessels have to strike a balance between their width the pressure of the blood moving against their walls and the force it takes to move that blood around in a bigger animal with a larger longer and branchier circulatory system blood flow ends up being slower since it's slower and the body is larger it takes longer for blood and the oxygen it carries to get places and the animal can't beat its heart faster or harder to speed things up because if it tried its heart would fail so as an animal grows in size its cells simply can't keep using oxygen at the same rate more work is needed to sort out how all these ideas apply to humans specifically but whatever the reason for children's elevated metabolisms the effect on drug dosing can be pretty dramatic so ultimately it's not that there are separate formulations because kids always need less medicine if anything it's so that a patient or their caregiver can more carefully adjust the dose they need for their body size liquid medications in particular can be carefully tailored to a child's weight and there are other reasons to have special formulas for kids too like that pills can be hard to swallow or even a choking hazard especially for younger children so lots of kids medicines avoid the issue by using chewables or liquids instead plus not all medications are recommended for children of all ages they might be ineffective or have more severe side effects in smaller kids or they just haven't been thoroughly tested yet the bottom line is if it isn't sold in a separate children's version it shouldn't be given to a child without consulting a pediatrician and you should always stick to the children's formulations when treating kids because that's the best way to ensure they get the right amount even though it may be more than what you'd take so remember if your human body experiences technical issues it's best to consult a professional thanks for watching this scishow compilation if you'd like to keep going we have a user's guide to the human brain as well and if you'd like to help us make more videos you can support us at patreon.com scishow you

Channel: SciShow

Views: 220,611

Rating: 4.9227762 out of 5

Keywords: SciShow, science, Hank, Green, education, learn, health, human body, temperature, fungus, michael aranda, sleep, depression, oversleep, self care, health problems, chocolate, cravings, pizza, magnesium, deficiency, hunger, ghrelin, memory, psychological, physiological, pregnancy, hormones, appendix, mammals, gut bacteria, immune response, appendicitis, appendectomy, antigens, Rh(D), blood type, dose, allometry, physiology, metabolism, weight-based dose, mass-specific metabolic rate, A User's Guide to the Human Body

Id: buwz62Ns1x8

Length: 22min 31sec (1351 seconds)

Published: Wed Jan 27 2021