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  • I’d like you to take a second and really look at yourself.

  • I don’t mean take stock of your life, which really isn't any of my business, but I mean just

  • look at your body.

  • Hold up a hand and wiggle it around. Take a sip of water. Hold your breath. Sniff the air.

  • These things are so simple for most of us that we don’t give them a moment’s thought.

  • But each one of those things is, oh, SO much more complex than it feels.

  • Every movement you make, every new day that you live to see, is the result of a

  • collection of systems working together to function properly.

  • In short, you, my friend, are a magnificent beast.

  • You are more convoluted and prolific and polymorphously awesome than you probably even

  • dare to think.

  • For instance, did you know that, if they were all stretched out, your intestines would be about as long

  • as a three story building is tall?

  • Or that by the time you reach old age, youll have produced enough saliva to fill more than

  • one swimming pool?

  • Or that you lose about two-thirds of a kilogram every year in dead skin cells? And you will

  • lose more than 50 kilograms of them in your lifetime? Just tiny, dried-up pieces of you, drifting

  • around your house, and settling on your bookshelves, feeding entire colonies of dust mites.

  • Youre your own little world.

  • And I’m here to help you get to know the body that you call a home, through the twin

  • disciplines of anatomy - the study of the structure and relationships between body parts,

  • and physiology - the science of how those parts come together to function, and keep

  • that body alive.

  • Anatomy is all about what your body is, physiology is about what it does. And together, they

  • comprise the science of us.

  • It’s a complicated science - I’m not gonna lie to you - and it draws on a lot of other

  • disciplines, like chemistry and even physics. And youll have to absorb a lot of new terms

  • - lots of Latin, gobs of Greek.

  • But this course isn't just gonna be an inventory of your

  • individual parts, or a diagram of how a slice of pizza gives you energy.

  • Because these disciplines are really about why youre alive right now, how you came

  • to be alive, how disease harms you, and how your body recovers from illness and injury.

  • It's about the big-picture things that we either spend most of our time thinking about,

  • or trying not to think about: death, and sex, and eating, and sleeping, and even the act

  • of thinking itself.

  • Theyre all processes that we can understand through anatomy and physiology.

  • If you pay attention, and if I do my job well enough, youll come out of this course with

  • a richer, more complete understanding not only of how your body works, to produce everything

  • from a handshake to a heart attacks, but I think youll also start to see that you

  • really are more than just the sum of your parts.

  • We have come to understand the living body by studying a lot of dead ones.

  • And for a long time, we did this mostly in secret.

  • For centuries, the dissection of human bodies was very taboo in many societies. And as a

  • result, the study of anatomy has followed a long, slow, and often creepy road.

  • The 2nd century Greek physician Galen gleaned what he could about the human form by performing

  • vivisections on pigs.

  • Da Vinci poked around dead bodies while sketching his beautifully detailed anatomical drawings,

  • until the pope made him stop.

  • It wasn’t until the 17th and 18th centuries that certified anatomists were allowed to

  • perform tightly regulated human dissections -- and they were so popular that they were

  • often public events, with admission fees, attended by the likes of Michelangelo and Rembrandt

  • The study of human anatomy became such a craze in Europe that grave-robbing became a lucrative,

  • if not legal, occupationuntil 1832, when Britain passed the Anatomy Act, which provided

  • students with plentiful corpses, in the form of executed murderers.

  • Today, students of anatomy and physiology still use educational cadavers to learn, in

  • person and hands-on, what’s inside a human body by dissecting them.

  • And it’s totally legal. The cadavers are volunteers -- which is what people mean when

  • they say theyredonating their body to science.”

  • So what have all of these dead bodies shown us?

  • Well, one big idea we see over and over is that the function of a cell or an organ or

  • a whole organism always reflects its form.

  • Blood flows in one direction through your heart simply because its valves prevent it

  • from flowing backward

  • In the same way, your your bones are strong and hard and this allows them to protect and

  • support all your soft parts.

  • The basic idea -- that what a structure can do depends on its specific form -- is called

  • the complementarity of structure and function.

  • And it holds true through every level of your body’s organization, from cell to tissue

  • to system.

  • And it begins with the smallest of the small: atoms.

  • Just like the chair youre sitting on, you are just a conglomeration of atoms -- about 7

  • octillion of them, to be precise.

  • Fortunately for both of us here, we've covered the basics of chemistry that every incoming

  • physiology student needs to know, in Crash Course Chemistry. So I’ll be referring

  • you there throughout the course, when it comes to how things work at the atomic level.

  • But the next level up from the chemistry of atoms and molecules includes the smallest

  • units of living things -- cells.

  • All cells have some basic functions in common, but they also vary widely in size and shape,

  • depending on their purpose.

  • For example! One of the smallest cells in your body is the red blood cell, which measures

  • about 5 micrometers across. Now contrast that with the single motor neuron that runs the

  • length of your entire leg, from your big toe to the bottom of your spine, about a meter

  • from end to end. Typically, cells group with similar cells

  • to form the next level of organization: tissues, like muscles, membranes and cavity linings,

  • nervous, and connective tissues. When two or more tissue types combine, they

  • form organs -- the heart, liver, lungs, skin and etcetera that perform specific functions

  • to keep the body running.

  • Organs work together and combine to get things done, forming organ systems. It’s how, like,

  • the liver, stomach, and intestines of your digestive system all unite to take that burrito

  • from plate to pooper.

  • And finally, all those previous levels combine to form the highest level of organization

  • -- the body itself.

  • Me and you and your dog -- were all glorious complete organisms, made from the precise

  • organization of trillions of cells in nearly constant activity.

  • This ability of all living systems to maintain stable, internal conditions no matter what

  • changes are occurring outside the body is called homeostasis, and it’s another major

  • unifying theme in anatomy and physiology.

  • Your survival is all about maintaining balance -- of both materials and energy.

  • For example, you need the right amount of blood, water, nutrients, and oxygen to create

  • and disperse energy, as well as the perfect body temperature, the right blood pressure,

  • and efficient movement of waste through your body, all that needs to stay balanced.

  • And by your survival depending on it? I mean that everyone’s ultimate cause of death

  • is the extreme and irreversible loss of homeostasis.

  • Organ failure, hypothermia, suffocation, starvation, dehydration -- they all lead to the same end,

  • by throwing off your internal balances that allow your body to keep processing energy.

  • Take an extreme and sudden case -- your arm pops off. If nothing is done quickly to treat

  • such a severe wound, you would bleed to death, right?

  • Butwhat does that really mean? What's gonna happen? How do I die?

  • Well, that arterial wound, if left untreated, will cause a drastic drop in blood pressure

  • that, in turn, will prevent the delivery of oxygen throughout the body.

  • So the real result of such an injury -- the actual cause of death -- is the loss of homeostasis.

  • I mean, you can live a full and healthy life without an arm. But you can’t live without

  • blood pressure, because without blood, your cells don’t get oxygen, and without oxygen,

  • they can’t process energy, and you die.

  • With so many connected parts needed to make your life possible, you can see how we need

  • a hyper-precise language to identify the parts of your body and communicate what’s happening to them

  • A doctor isn't gonna recommend a patient for surgery by telling the surgeon that the patient

  • has anachey belly.”

  • Theyre going to need to give a detailed description -- essentially, it's like a verbal map

  • So, over time, anatomy has developed its own standardized set of directional terms that

  • described where one body part is in relation to another.

  • Imagine a person standing in front of you -- this is what’s called the classic anatomical

  • position -- where the body is erect and facing straight ahead, with arms at the sides and

  • palms forward.

  • Now imagine slicing that person into different sections, or planes. Don't imagine it too

  • graphically though.

  • The sagittal plane comes down vertically and divides a body or organ in left and right

  • parts.

  • If you imagine a plane parallel to the sagittal plane, but off to one side, that plane is

  • the parasagittal.

  • The coronal, or frontal plane splits everything vertically into front and back.

  • And the transverse, or horizontal plane divides the body top and bottom.

  • Look at that body again and youll notice more divisions, like the difference between

  • the axial and appendicular parts.

  • Everything in line with the center of the body -- the head, neck, and trunk -- are considered

  • axial parts, while the arms and legs -- or appendages-- are the appendicular parts that

  • attach to the body’s axis.

  • Everything at the front of your body is considered anterior, or ventral, and everything in the back

  • is posterior, or dorsal.

  • So your eyes are anterior, and your butt is posterior, but you’d also say that your breastbone

  • is anterior to, or in front of, the spine, and that the heart is posterior to, or behind

  • the breastbone.

  • Features toward the top of your body, like your head, are considered superior, or cranial,

  • while structures that are lower down are inferior, or caudal.

  • So the jaw is superior to the lungs because it’s above them, while the pelvis is inferior

  • to the stomach because it’s below it.

  • And, there's more: if you imagine that center line running down the axis of a body, structures

  • toward that midline are called medial, while those farther away from the midline are lateral.

  • So the arms are lateral to the heart, and the heart is medial to the arms.

  • Looking at the limbs -- your appendicular parts of your body -- you’d call the areas

  • closer to the center of the trunk proximal, and those farther away distal.

  • In anatomy-talk, your knee is proximal to your ankle because it’s closer to the axial

  • line, while a wrist is distal to the elbow because it’s farther from the center.

  • Okay, so pop quiz!

  • I’m eating a club sandwich -- I'm not, I wish I was, but imagine I am. I’m so ravenous

  • and distracted that I forget to take out that little frilly toothpick at the top, and I

  • end up swallowing it with a raft of turkey, bacon, and toast.

  • A fragment of the toothpick gets lodged somewhere in here, and my doctor takes an x-ray, and

  • says I need surgery.

  • Using anatomical language, how would she direct the surgeon to that tiny wooden stake inside of me?

  • She might describe it as beingalong the medial line, posterior to the heart, but anterior

  • to the vertebrae, inferior to the collarbone, but superior to the stomach.”