Name: 內分泌系統，第1部分--腺體和激素。速成班A&P #23 (Endocrine System, part 1 - Glands & Hormones: Crash Course A&P #23)
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I've invited you all here today because
I wanted to talk to you about some

關係子句

進階被動語態

I've been hearing a lot of unfair, unseemly, and
unscientific generalizations being made lately.

And they mostly have to do with sex. And your hormones.

People have a nasty habit of equating “hormones”
with a particular set of behaviors and conditions,

most of which have to do with reproduction,
or sexual development, or acts that include

what my brother John has referred to as “skoodilypooping.”

For example, people will say that “hormones”
are why Kevin has zits, and is being all moody,

or why Hannah, who's three months pregnant,
just cried watching a commercial for car insurance

-- which, let's be honest, I do that too.

Now, I'm not saying that hormones aren't
at the root of sexual attraction, or zits,

or occasional bouts of extreme emotion, because
they are. That's just not all that they do.

When people talk about “hormones” in
the contexts that I just mentioned,

But sex hormones are just one kind of hormone
that you have coursing through your body right now.

In fact, there are at least 50 different types
of these chemical messengers at work in your

body at this very minute, but only a very few
of them have anything at all to do with sex.

The truth is, from birth to death, just about
every cell and function in your body is under

They're floating through your blood, regulating
your metabolism, your sleep cycle, your response

to stress, and the general and incredibly important
overall homeostasis that keeps you not dead.

Some hormones are just there to make other
hormones trigger even more hormones -- in

a kind of chemical relay race that biologists
refer to, rather elegantly, as “cascades.”

These hormones run through you no matter what
your mood is, or whether you have zits.

So the reality is: We're all hormonal ... all
of the time.

OK, to begin to understand our hormones -- and
the endocrine system that produces, releases,

and re-absorbs them -- we have to step back
and take a broad view.

Not just by emphasizing that sex hormones aren't
the only hormones you have -- but also by

looking at how your hormones interact with
your other organ systems.

Because, if anything, your body has two bosses
-- two complementary systems that are constantly

shouting instructions over each other, to
all of your bits and pieces.

Both your endocrine system and your nervous
system are constantly trafficking information

around your corpus, gathering intel, making
demands, controlling your every move. They

just have totally different ways of doing
it.

Your nervous system uses lightning-fast
electrochemical action potentials,

delivered by an expressway made of
neurons to specific cells and organs.

But your endocrine system prefers a slower,
wider stream of data.

It secretes hormones that travel through your
blood -- NOT through neurons -- so they move more

slowly, but they also produce widespread effects
that last a whole lot longer than an action potential.

Now, compared to your heart or brain or other,
arguably more glamorous organs, your endocrine

system's organs and glands are kinda small
and lumpy.

They're also rogues -- instead of being all
nestled together like in your other organ systems,

these guys are scattered all over the place, from your
brain to your throat, to your kidneys, to your genitals.

A gland is a just any structure that makes
and secretes a hormone. And the master gland

in your body is the pituitary, which produces
many hormones that signal other glands -- like

the thyroid, parathyroid, adrenal, and pineal
glands -- to make their own hormones.

The endocrine system also includes a few organs
-- like the gonads, the pancreas, and the

placenta in pregnant women -- all of which
have some other non-hormonal functions and

And technically the hypothalamus in your brain
is in the endocrine club too, since in addition

to all of its busy brain duties, it does produce
and release hormones.

So, thanks to these glands and organs, you've got
all these hormones diffusing through your blood,

doing all sorts of different things, but the thing to
remember about them is that a hormone can only

trigger a reaction in specific cells -- their so-called
target cells -- that have the right receptors for it.

So, just like some keys can open many locks,
while others only work with one, so too can

the hormone-target-cell relationship either
be widespread or localized.

You're probably gonna want an example of
that. So, your thyroid -- at the bottom of

your throat -- produces the hormone thyroxine,
which stimulates metabolism and binds to receptors

But your pituitary -- which is nestled all
comfy under your brain -- produces follicle-stimulating

hormone, which helps regulate growth and triggers
sexual maturity, and it only targets specific

So how do hormones bind to their target cells?

Well, chemically, most hormones are either
made of amino acids -- including their more

complex structures like peptides or proteins
-- or they're derived from lipids, like cholesterol.

And this is key, because a hormone's chemical
structure determines if it's water soluble,

like most amino acid-based ones are, or lipid
soluble, like steroids are.

Solubility is important because your cell
membranes are made of lipids.

That means that water soluble ones can't
get across them. So target cells for those

kinds of hormones have receptors for them
on the outside of their membranes.

Lipid-soluble hormones, on the other hand,
can just basically glide right through that

cell membrane, so their receptor sites are
inside their target cells.

Either way, when a target cell is activated,
the hormone alters its activity, by either

increasing or decreasing some of its functions
-- usually with the goal of maintaining your

body's homeostasis in one way or another.

So, if hormones are keeping your body IN balance,
what's putting your body out of balance?

I don't know -- could I interest you in
some pie?

If you have a couple of nice, generous helpings
of strawberry-rhubarb pie -- and just to make

things interesting, let's say they're a la mode --
your blood glucose level is gonna go through the roof.

And the pancreas regulates your blood sugar by
releasing two different hormones -- insulin and

glucagon. Once you have a belly full of that pie,
beta cells in your pancreas release insulin, which

helps lower your blood sugar by increasing
the rate at which your cells store the sugar

either as glycogen or as fat for later use.

Now, let's say you've done the opposite:
You've eaten no pie -- you're pie-less

-- in fact, you've eaten nothing for hours.

If your blood sugar drops too low, then alpha
cells in the pancreas will instead send out

glucagon, which helps raise your blood sugar
levels, in part by decreasing the storage

of sugar in your cells, and triggering their
release of glucose back into the blood.

Lots of different endocrine-related illnesses
-- like diabetes or hyperthyroidism -- tend

to be the result of either hyper (too much)
or hypo (too little) secretion of certain

hormones, which throw your homeostasis off
balance.

But there are lots of more common -- and less
obvious -- ways your hormones can get out

of balance, not because of some disorder,
but because these signaling chemicals are

just caught up in a chain reaction, which
can take a while to subside.

Some hormones just exist to control other
hormones, which in turn control still more hormones.

So as soon as one starts to trickle out, you can
pretty quickly wind up with a cascade on your hands.

You've got a few different hormone cascades
going on at any given moment, but one of the

big ones -- one that's really worth understanding
-- is the hypothalamic-pituitary-adrenal axis,

or the HPA axis, because you don't want
to have to say that every time.

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內分泌系統，第1部分--腺體和激素。速成班A&P #23 (Endocrine System, part 1 - Glands & Hormones: Crash Course A&P #23)

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