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- [Voiceover] Every hormone
in the body is either

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categorized as a steroid or a nonsteroid.

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Now these steroid hormones
are gonna be lipid

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soluble, that means they can go right

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through the cell membrane.

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Really they're pretty
close to cholesterol.

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While the nonsteroid hormones are really

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looking like proteins, and these proteins

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are water soluble.

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They can not go through the cell membrane.

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Now let's do a little more information

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on steroid hormones.

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Mentioned they're lipid
soluble, which means

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they go right through the cell membrane.

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They're actually made from cholesterol.

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That's why they're similar to cholesterol.

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They're able to enter
right into the target cell.

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Once they enter in, they
can activate specific

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genes to make a protein.

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So the hormone itself
can actually activate

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the gene inside the cell.

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Now these are slower than the nonsteroid

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because they go through the membrane,

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find the right gene, and activate it.

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So we're talking minutes to
hours for an activation here.

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Here we're looking at, that blue up top is

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the fluid between two cells.

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The top part says
capillary, that's the blood.

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So the hormone, in this
case the steroid-based

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hormone, can come through
blood and get into

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the interstitial fluid, the fluid

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between the cell and capillary.

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It can then diffuse right
through the cell membrane.

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That's because the steroid
hormones are lipid soluble.

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Well it goes in, eventually
activates a gene,

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but activating a gene is
gonna start protein synthesis.

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With protein synthesis,
you make a new protein.

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That new protein can alter
that cell's activity,

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it could be transported to another cell,

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but there's some reason
why the body triggered

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the production of this protein.

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It's really four steps
here: hormone diffuses

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through membrane, hormone
activates the gene,

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which then triggers protein synthesis,

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and the protein then will change this cell

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or some other cell's activity or even be

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a structural, help to build something.

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The nonsteroid hormones, well, remember

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they're water soluble.

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That means they cannot go
through the cell membrane.

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And since they can't go through the cell

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membrane, they must bind to receptors

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on top of the cell membrane.

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So the nonsteroid
hormones will stay outside

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the cell but bind to an external receptor.

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Once they bind to this external receptor,

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they then go through pretty
much this intermediate

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mechanism, referred to
as a secondary messenger.

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So it takes the message from the hormone,

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which is outside the cell, that message is

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translated to the internal mechanism,

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and that internal
mechanism carries it along.

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This is usually the faster
method because those

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internal mechanisms have
very specific processes.

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So here we go.

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This is gonna be your nonsteroid hormone.

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Same basic stuff, the
blood capillary's up top,

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interstitial fluid's
the middle, then you see

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the target cell membrane is a double-faced

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lipid dilator.

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We can notice that the receptors now

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are facing outside the cell.

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So the hormone binds to the receptor.

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The receptor, then, can
go through and activate

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a secondary messenger because the primary

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messenger or first messenger
was the actual hormone.

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The hormone couldn't come
in so it's transferred

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its information to a secondary messenger.

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That secondary messenger
could then activate

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an enzyme which might
activate another enzyme

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which might activate another enzyme,

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and eventually the final product is there.

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So you might have three different enzymes,

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you might have two, you might have five.

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It's not an exact always three enzymes.

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Depends on the cycle.

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The important part here is they're using

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a secondary messenger.

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The hormone never came in.

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Now these hormones,
those may physically be

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a steroid-based or
nonsteroid-based, whether it's

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lipid soluble or water soluble.

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A large amount of these
hormones are dealing

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with homeostatic control of the mechanisms

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in your body.

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They're helping to keep them working,

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helping to keep them safe, and making sure

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everything runs like clockwork.

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Next is where these negative feedback

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loops come in.

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In the case of the endocrine,
the endocrine gland

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can be the control center,
can send information

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out, in this case
sending the hormones out,

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and get information back.

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The hormones travel from
the endocrine gland,

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control center, and then
travel to the effector,

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whatever is going to make a change.

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The target tissues or
organs, whatever is making

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that change, that is the effector.

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Once an action has been
performed, it'll then

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send information back
to the endocrine glands.

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But it will be in
communication the entire time.

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There's always a little bit of feedback

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bouncing back, saying
"we need more hormone,"

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"we need less hormone."

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So helping to control
the amounts of hormone.

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You can pretty much think
of a negative feedback

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loop as a self-correcting loop.

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If something's going wrong, you send back

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the negative information.

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The control center fixes it, sends it back

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forward, hopefully it's right this time.

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So negative feedback loops are trying

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to correct problems.

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Here we have a basic idea
of what we're looking at.

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Controlled variable, very simplistic.

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If that particular variable
ends up being too low,

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the entering gland or control center

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will get that information.

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It could then send a
hormone to a target cell,

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target tissues, whatever's
not working properly,

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which then, once the
hormone's there, it can

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reverse it and go back
up to proper set point.

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So the endocrine glands can tell us about

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what is going on in the
body, send hormones out

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to correct what's wrong.