Voiceover: I want you to imagine with me
that you're a cell in the brain.
Let's say you're a member of the hypothalamus right here.
As a part of the hypothalamus
one of your jobs is to regulate how much fluid
is in the blood volume at any given time.
You just got informed by another part of the brain
that your body cell down in the kidneys right here
has been making urine like a madman all day,
and now the fluid volume in the blood is a little bit low.
You want to tell him to stop
but how do you go about doing that?
I mean one way the body communicates is
through the nervous system
and sending messages down the hardwired,
prelaid tracks of the nervous system through nerves
but there isn't really an established connection
between you and him.
What you decide to do is you decide to
put a message in a bottle of sorts
and float it down the bloodstream to him
and hope that it gets there.
You send that message his way
and he receives it.
He opens that message and he sees
that you want him to close the permeability to water
and he does that
and fluid volume begins to be restored again.
That process of sending a message
from one part of the body to another part of the body
through the bloodstream
forms the basis of the endocrine system.
The endocrine system.
The endocrine system is a system of glands
that produce chemical messages called hormones
that travel from one part of the body
to another part of the body through the blood
in order to elicit an effect.
In order to make a change in what's going on
in a different part of the body.
In the effects that are caused by the endocrine system
cooperate with the nervous system
in order to control the body's internal environment
and homeostasis.
The endocrine system and the nervous system
are really related.
They're almost like cousins.
They're really similar
but they're kind of unique.
The nervous system is kind of like the hare
in the children's story with the tortoise and the hare
and the endocrine system would be the tortoise.
The nervous system is really, really fast
and you see results in milliseconds.
The endocrine system in comparison is fairly slow
and it might take minutes to even days or weeks
to see the effects of these hormones.
Like the children's story with the tortoise
and with the hare,
the tortoise as fast as he go
he runs out of steam pretty quickly
and the endocrine system as it goes a little bit
slower but it will last longer.
The effects while slower
had a more lasting effect in the body
with the endocrine system.
Anyway, the chemical messages called hormones
that the endocrine system utilizes
they can be broken down into three distinct classes.
First you have proteins and polypeptides.
Proteins and polypeptide hormones
like any other proteins in the body
are made up of amino acids and they can be really small.
As small as three or so amino acids
which is pretty tiny when you think about it
because an amino acid is a fairly small collection of atoms
and if you're talking about three amino acids
that's only a few atoms all the way up to
hundreds and hundreds of amino acids
in a polypeptide chain.
Typically after you get about a hundred amino acids
in a chain you start calling it a protein
and that holds true for hormones as well.
The second class after proteins and polypeptides
are steroid hormones.
Unlike proteins and polypeptides
that are made up of amino acids
steroid hormones are typically derived from cholesterol
which is a lipid.
From cholesterol.
Steroids are made up of lipids
and have lipid-like qualities like they're not charge
and they can pass through cell membranes.
That might mean the receptor
instead of being on the outside of the cell
it's on the inside of the cell.
You've got proteins and you've got steroids
and then you've got a class called tyrosine derivatives.
Tyrosine is an amino acid
and this class of hormones,
the reasons it's separate is that
they're derived from tyrosine.
Tyrosine can be manipulated in order to make
a couple different hormones.
The two main classes of tyrosine derivatives are
thyroid hormones and catecholamines.
Catecholamines, I hope I spelled that right.
Catecholamines.
Catecholamines are the hormones
that are made in the adrenal medulla
and they include epinephrine and nor epinephrine.
A little bit more common name
outside of the medical community
for epinephrine is adrenaline.
Adrenaline is a little bit more familiar
because we hear it when you're really excited
and your fight or flight response.
These are the three main classes of hormones
and we see that they're classified by structure
but they're also classified by function
in a separate system.
Even though all these hormones
are functioning in the endocrine system
not all of them have endocrine function.
There's a class of hormones
that are considered to have autocrine function
and these are hormones that elicit a response
at the cell that they're made
or the cell immediately next to
the cell that makes the hormone.
In addition to autocrine signalling
there's paracrine signals.
This is more the regional effect.
One example of paracrine signals
are between the hypothalamus and the pituitary gland
which I'll show you in a second.
Those are really close.
Yeah, there's not a hard line that gets drawn
with where paracrine signal function ends
but generally these are regionally acting signals.
Then the last class are the endocrine signals.
Those are the classic hormones
that are set to function at a distance in the body
and their response is elicited somewhere far away.
Let's say the pituitary gland
traveling all the way down to the gonads.
That's a pretty long distance in terms of hormone size
and blood vessel length.
Those are called endocrine glands.
Now that we've covered how hormones are classified
I want to talk about the main organs
of the endocrine system
that use these hormones to communicate.
I went ahead and pre wrote out
to save a little bit of time.
The first organ that I want to talk about
in the endocrine system is the hypothalamus.
The hypothalamus is a member of the endocrine system
but it's also a member of the nervous system.
It's right here in the brain.
It's about the size of a grape.
As a member of the nervous system
it's taking in the signals
that are being stimulated by the sensory nerves.
It takes those signals
and it kind of funnels them into the endocrine system
through the pituitary gland
by controlling the pituitary gland.
The pituitary gland is often known as the master gland.
It's situated right here below the hypothalamus
and if the hypothalamus is about
the size of a grape in the body,
the pituitary gland is about the size of a green pea
and it's tiny but it's role is huge
in that it is principally involved in
stimulating the other endocrine glands
which are ultimately gonna
cause any of the effects that are happening in the body.
The first organ that it stimulates
going down the list here is the thyroid gland.
It stimulates the thyroid gland
through thyroid stimulating hormone.
The thyroid gland is a gland that wraps around
the trachea which is your windpipe
and you can feel it when you swallow,
but the thyroid gland's main role
is regulating our body's metabolism.
Up regulating or down regulating the entire body
and it does that through the thyroid hormones T3 and T4.
Another name for T3 is triiodothyronine
and another name for T4 is thyroxine,
but those are the thyroid hormones
that are a member of the thyrosine derivatives
that I was talking about a little bit earlier.
Behind the thyroid gland are four spots
that are kind of collectively known
as the parathyroid gland.
I'm drawing them on the front
but I want to be clear
that these spots are on the back of the thyroid gland
and the parathyroid gland is principally
or chiefly involved in regulating
our body's calcium levels.
It does that through its hormone parathyroid hormone.
Moving down the list we have the adrenal glands
right here on top of the kidneys.
They're called adrenal glands
because they're adjacent to the kidneys
and another name for the kidneys are the,
the whole kidney system is the renal system.
The adrenal glands are stimulated
by the pituitary's release of adrenocorticotropic hormone
and then they ultimately release their hormones.
There are two separate areas of the adrenal glands.
You've got the cortex of the adrenal glands
which is the outside and the medulla
which is the inside of the adrenal glands.
The cortex is where the adrenal
steroid hormones come from
and so you got your glucocorticosteroids
and your mineralocorticosteroids
and those are things like cortisol and aldosterone.
Those have a lot of functions in the body
as far as regulating fluid volume
and the stress response
and in the medulla
that's where the catecholamine hormones are made.
Again, those catecholamines were the second class
of thyrosine derivatives that I mentioned earlier.
Moving down the list even further
we have the gonads.
In females those are your ovaries.
In males your testes.
The gonads are stimulated by
the pituitary's release of FSH and LH
which is follicle stimulating hormone
and luteinizing hormone.
The gonads then take that stimulation
and release their hormones, the sex hormones.
In ladies that's mostly progesterone and estrogen
and in males testosterone.
Those are your gonads.
Outside of that pituitary signalling system
is the pancreas right here.
The pancreas isn't stimulated
by the pituitary gland directly
but it does release some pretty important hormones
insulin and glucagon which function
to regulate the blood sugar level.
Again, the blood sugar level is pretty tied
into the metabolism as glucose is
kind of the backbone molecule that we get
all of our energy from.