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I’d like you to take a second and really
look at yourself.
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I don’t mean take stock of your life, which
really isn't any of my business, but I mean just
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look at your body.
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Hold up a hand and wiggle it around. Take a sip of
water. Hold your breath. Sniff the air.
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These things are so simple for most of us
that we don’t give them a moment’s thought.
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But each one of those things is, oh, SO much
more complex than it feels.
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Every movement you make, every new day
that you live to see, is the result of a
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collection of systems working together to
function properly.
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In short, you, my friend, are a magnificent
beast.
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You are more convoluted and prolific and
polymorphously awesome than you probably even
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dare to think.
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For instance, did you know that, if they were all stretched out, your intestines would be about as long
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as a three story building is tall?
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Or that by the time you reach old age, you’ll
have produced enough saliva to fill more than
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one swimming pool?
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Or that you lose about two-thirds of a kilogram
every year in dead skin cells? And you will
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lose more than 50 kilograms of them in your lifetime?
Just tiny, dried-up pieces of you, drifting
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around your house, and settling on your bookshelves,
feeding entire colonies of dust mites.
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You’re your own little world.
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And I’m here to help you get to know the
body that you call a home, through the twin
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disciplines of anatomy - the study of the
structure and relationships between body parts,
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and physiology - the science of how those
parts come together to function, and keep
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that body alive.
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Anatomy is all about what your body is, physiology
is about what it does. And together, they
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comprise the science of us.
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It’s a complicated science - I’m not gonna
lie to you - and it draws on a lot of other
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disciplines, like chemistry and even physics.
And you’ll have to absorb a lot of new terms
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- lots of Latin, gobs of Greek.
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But this course isn't just gonna be an inventory of your
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individual parts, or a diagram of how a
slice of pizza gives you energy.
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Because these disciplines are really about
why you’re alive right now, how you came
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to be alive, how disease harms you, and how
your body recovers from illness and injury.
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It's about the big-picture things that we
either spend most of our time thinking about,
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or trying not to think about: death, and sex,
and eating, and sleeping, and even the act
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of thinking itself.
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They’re all processes that we can understand
through anatomy and physiology.
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If you pay attention, and if I do my job well
enough, you’ll come out of this course with
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a richer, more complete understanding not
only of how your body works, to produce everything
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from a handshake to a heart attacks, but I
think you’ll also start to see that you
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really are more than just the sum of your parts.
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We have come to understand the living body
by studying a lot of dead ones.
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And for a long time, we did this mostly in
secret.
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For centuries, the dissection of human bodies
was very taboo in many societies. And as a
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result, the study of anatomy has followed
a long, slow, and often creepy road.
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The 2nd century Greek physician Galen gleaned
what he could about the human form by performing
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vivisections on pigs.
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Da Vinci poked around dead bodies while sketching
his beautifully detailed anatomical drawings,
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until the pope made him stop.
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It wasn’t until the 17th and 18th centuries
that certified anatomists were allowed to
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perform tightly regulated human dissections
-- and they were so popular that they were
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often public events, with admission fees,
attended by the likes of Michelangelo and Rembrandt
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The study of human anatomy became such a craze
in Europe that grave-robbing became a lucrative,
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if not legal, occupation … until 1832, when
Britain passed the Anatomy Act, which provided
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students with plentiful corpses, in the form
of executed murderers.
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Today, students of anatomy and physiology
still use educational cadavers to learn, in
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person and hands-on, what’s inside a human
body by dissecting them.
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And it’s totally legal. The cadavers are
volunteers -- which is what people mean when
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they say they’re “donating their body
to science.”
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So what have all of these dead bodies shown
us?
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Well, one big idea we see over and over is
that the function of a cell or an organ or
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a whole organism always reflects its form.
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Blood flows in one direction through your
heart simply because its valves prevent it
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from flowing backward
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In the same way, your your bones are strong
and hard and this allows them to protect and
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support all your soft parts.
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The basic idea -- that what a structure can
do depends on its specific form -- is called
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the complementarity of structure and function.
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And it holds true through every level of your
body’s organization, from cell to tissue
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to system.
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And it begins with the smallest of the small:
atoms.
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Just like the chair you’re sitting on, you are
just a conglomeration of atoms -- about 7
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octillion of them, to be precise.
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Fortunately for both of us here, we've covered
the basics of chemistry that every incoming
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physiology student needs to know, in Crash
Course Chemistry. So I’ll be referring
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you there throughout the course, when it comes
to how things work at the atomic level.
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But the next level up from the chemistry of
atoms and molecules includes the smallest
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units of living things -- cells.
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All cells have some basic functions in common,
but they also vary widely in size and shape,
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depending on their purpose.
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For example! One of the smallest cells in
your body is the red blood cell, which measures
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about 5 micrometers across. Now contrast that
with the single motor neuron that runs the
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length of your entire leg, from your big toe
to the bottom of your spine, about a meter
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from end to end.
Typically, cells group with similar cells
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to form the next level of organization: tissues,
like muscles, membranes and cavity linings,
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nervous, and connective tissues.
When two or more tissue types combine, they
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form organs -- the heart, liver, lungs, skin
and etcetera that perform specific functions
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to keep the body running.
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Organs work together and combine to get things
done, forming organ systems. It’s how, like,
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the liver, stomach, and intestines of your
digestive system all unite to take that burrito
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from plate to pooper.
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And finally, all those previous levels combine
to form the highest level of organization
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-- the body itself.
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Me and you and your dog -- we’re all glorious
complete organisms, made from the precise
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organization of trillions of cells in nearly
constant activity.
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This ability of all living systems to maintain
stable, internal conditions no matter what
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changes are occurring outside the body is
called homeostasis, and it’s another major
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unifying theme in anatomy and physiology.
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Your survival is all about maintaining balance
-- of both materials and energy.
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For example, you need the right amount of
blood, water, nutrients, and oxygen to create
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and disperse energy, as well as the perfect
body temperature, the right blood pressure,
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and efficient movement of waste through your
body, all that needs to stay balanced.
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And by your survival depending on it? I mean
that everyone’s ultimate cause of death
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is the extreme and irreversible loss of homeostasis.
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Organ failure, hypothermia, suffocation, starvation,
dehydration -- they all lead to the same end,
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by throwing off your internal balances that
allow your body to keep processing energy.
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Take an extreme and sudden case -- your arm
pops off. If nothing is done quickly to treat
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such a severe wound, you would bleed to death,
right?
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But … what does that really mean? What's
gonna happen? How do I die?
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Well, that arterial wound, if left untreated,
will cause a drastic drop in blood pressure
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that, in turn, will prevent the delivery of
oxygen throughout the body.
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So the real result of such an injury -- the
actual cause of death -- is the loss of homeostasis.
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I mean, you can live a full and healthy life
without an arm. But you can’t live without
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blood pressure, because without blood, your
cells don’t get oxygen, and without oxygen,
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they can’t process energy, and you die.
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With so many connected parts needed to make
your life possible, you can see how we need
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a hyper-precise language to identify the parts
of your body and communicate what’s happening to them
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A doctor isn't gonna recommend a patient for
surgery by telling the surgeon that the patient
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has an “achey belly.”
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They’re going to need to give a detailed
description -- essentially, it's like a verbal map
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So, over time, anatomy has developed its own
standardized set of directional terms that
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described where one body part is in relation
to another.
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Imagine a person standing in front of you
-- this is what’s called the classic anatomical
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position -- where the body is erect and facing
straight ahead, with arms at the sides and
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palms forward.
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Now imagine slicing that person into different
sections, or planes. Don't imagine it too
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graphically though.
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The sagittal plane comes down vertically and
divides a body or organ in left and right
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parts.
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If you imagine a plane parallel to the sagittal
plane, but off to one side, that plane is
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the parasagittal.
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The coronal, or frontal plane splits everything
vertically into front and back.
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And the transverse, or horizontal plane divides
the body top and bottom.
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Look at that body again and you’ll notice
more divisions, like the difference between
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the axial and appendicular parts.
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Everything in line with the center of the
body -- the head, neck, and trunk -- are considered
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axial parts, while the arms and legs -- or
appendages-- are the appendicular parts that
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attach to the body’s axis.
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Everything at the front of your body is considered
anterior, or ventral, and everything in the back
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is posterior, or dorsal.
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So your eyes are anterior, and your butt is
posterior, but you’d also say that your breastbone
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is anterior to, or in front of, the spine,
and that the heart is posterior to, or behind
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the breastbone.
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Features toward the top of your body, like
your head, are considered superior, or cranial,
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while structures that are lower down are inferior,
or caudal.
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So the jaw is superior to the lungs because
it’s above them, while the pelvis is inferior
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to the stomach because it’s below it.
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And, there's more: if you imagine that center
line running down the axis of a body, structures
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toward that midline are called medial, while
those farther away from the midline are lateral.
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So the arms are lateral to the heart, and
the heart is medial to the arms.
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Looking at the limbs -- your appendicular
parts of your body -- you’d call the areas
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closer to the center of the trunk proximal,
and those farther away distal.
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In anatomy-talk, your knee is proximal to
your ankle because it’s closer to the axial
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line, while a wrist is distal to the elbow
because it’s farther from the center.
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Okay, so pop quiz!
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I’m eating a club sandwich -- I'm not, I
wish I was, but imagine I am. I’m so ravenous
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and distracted that I forget to take out that
little frilly toothpick at the top, and I
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end up swallowing it with a raft of turkey,
bacon, and toast.
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A fragment of the toothpick gets lodged somewhere
in here, and my doctor takes an x-ray, and
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says I need surgery.
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Using anatomical language, how would she direct
the surgeon to that tiny wooden stake inside of me?
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She might describe it as being “along the
medial line, posterior to the heart, but anterior
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to the vertebrae, inferior to the collarbone,
but superior to the stomach.”
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That would give the surgeon a pretty good
idea of where to look -- in the esophagus,
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just above to the stomach! I warned you at
the beginning: Lots of terms!
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But all those terms might have just saved
my life. And it’s the end of your first
00:10:21
lesson, and you’ve already started to talk
the talk.
00:10:24
Today you learned that anatomy studies the
structure of body parts, while physiology
00:10:27
describes how those parts come together to
function. We also talked about some of these
00:10:31
disciplines’ central principles, including
the complementarity of structure and function,
00:10:35
the hierarchy of organization, and how the
balance of materials and energy known as homeostasis
00:10:40
is really what keeps you alive. And then we
wrapped it all up with a primer on directional
00:10:45
terms, all held together with a toothpick.
00:10:47
Thank you for watching, especially to our Subbable
subscribers, who make Crash Course available
00:10:51
not just to themselves, but also everyone
else in the world. To find out how you can
00:10:56
become a supporter, just go to subbable.com.
00:10:58
This episode was written by Kathleen Yale,
edited by Blake de Pastino, and our consultant,
00:11:02
is Dr. Brandon Jackson. Our director and editor
is Nicholas Jenkins, the script supervisor
00:11:07
is Valerie Barr, the sound designer is Michael
Aranda, and the graphics team is Thought Café.
