Throughout your life,
you go through many remarkable phases of metamorphosis,
and none of them are as uncomfortable as when you morph
from the adorable pudgy caterpillar of childhood
and spread your wings as an awkward teenage butterfly.
Not only are our bodies flooded with signals
to become sexually mature,
hair starts growing in strange places,
voices change, your emotions are all over the place,
bodies are growing in every which direction,
and so many secretions.
All of these changes,
as well as dozens of others that you experience
on timescales ranging from seconds to years,
are mediated by one of the strangest systems
in that already peculiar sack of meat you call a body,
the endocrine system and its hormone messengers.
To understand why this chemical soup exists,
we first need to think about the Mongol Empire, wait, what?
(upbeat music)
Hey, smart people, Joe here.
So the Mongols,
Kublai Khan, in the mid 1200s,
reigned over the largest empire in history up to that point,
and he had a problem.
Let's say Kublai, Mr. Khan, Emperor K had an idea.
How do you get it to the farthest reaches of your empire
and make sure that every distant feudal lord works together
for the good of the whole?
Not to mention,
how do you keep stability in your vast empire
before the age of lightspeed communications?
He sent emissaries to deliver his message
and make sure that it was carried out.
Your body has the same problem.
It has to send instructions to its distant reaches
to coordinate stability, peace,
and responses to the external environment,
even the occasional invader.
But instead of emissaries and ambassadors, your body sends
out tiny chemical messengers called hormones.
And instead of roads,
they travel through your circulatory system
to find the cells or organs that need to heed their message.
Hormones tell us many things,
including when we're hungry, when to sleep,
when danger is near, and even when to grow into a new body.
This problem of how to send messages over long distances
and across hugely varying timescales
is one that's likely even older than multicellular life.
This is a cellular slime mold.
They start life as individual amoeba blobbies,
but when their environment gets stressful,
like when there's not enough food,
they secrete a chemical signal that tells them to pile up
with their neighbors until they slither together
like a single slimy slug.
Thousands of amoebas act together like one,
like minions to their chemical messenger overlord,
eventually even morphing into weird tree-like structures
that allow a few lucky individuals to escape as spores
to better and more fruitful lands.
Now you might not think you have a lot in common
with a slime mold,
but they're faced with the same problem your body is.
How do you get many individual cells to communicate,
coordinate, and cooperate over long distances
and even undergo major changes?
The answer, secreted chemical messages.
I mean, think about it,
that chemically-induced slime mold metamorphosis,
isn't that unlike what happens during puberty?
I mean, you're just living your life and then bam,
your body is flooded with chemicals,
setting off a series of weird and wonderful changes.
- [Narrator] This gradual and irregular readjustment
of the glandular system is almost certain
to make Johnny nervous, excitable,
and a little emotionally unstable.
- This is the central problem
that all multicellular creatures have to solve.
Bodies need a coordinated communication system
so that all of their parts know what to do
and when to do it,
whether it's to induce changes
or to keep the body nice and stable
in the face of environmental challenges.
In humans, that means relaying messages
between 30 trillion cells spread among dozens
of different interacting systems,
a vast metropolis of intermingling cellular mishmash.
Wait, isn't that what the nervous system's for,
I mean, taking information from one cell
and sending it to different parts of the body?
For most of medical history,
we thought that every process from fertility, to appetite,
to bodily temperature was controlled by our nervous system.
But in the mid 1800s,
that way of thinking started to change,
thanks to some castrated chickens.
(chicken cackles loudly) For hundreds of years,
people knew that castrated male chickens stayed tender
and delicious instead of becoming not-so-tasty
and not-so-friendly roosters.
But in 1849, for some reason,
German zoologist, Arnold Berthold, decided to put testicles
back into some of those castrated male chickens.
And he noticed that they matured into normal roosters.
The transplanted testicles had only connected
to the bloodstream and not the nervous system.
That told him that the grow sexy rooster feathers signal
was carried in the blood and not the nerves.
Around the same time,
another German doctor was busy taking people's temperatures,
25,000 people's temperatures,
adding up to millions of total readings.
When he averaged those millions of temperatures out,
he got 98.6 degrees Fahrenheit,
which is what most people think of
as normal body temperature.
But the really interesting thing he found was that,
two individuals may have different normal body temperatures,
varying by a degree or more.
But within an individual healthy body,
temperature was kept remarkably stable.
They just didn't know what was doing it.
It took more than 50 years for scientists to figure out
how these huge bodily changes,
like the roosters and their testes,
and the way that bodies keep themselves from changing,
like with temperature, are controlled.
And it turns out, they're mostly controlled
by the same thing, hormones.
All of these hormone messengers
and the tissues that make them, control them,
and shuttle them throughout the body are known
as the endocrine system.
It was the last major body system identified by doctors
because those chemical messages and the parts of cells
that sense them are all basically invisible.
Today we know of more than 50 hormones,
manufactured by at least nine lumps of tissue
that are spread through your body called glands.
Now, once hormones are sent into the bloodstream,
they travel around until they reach the right target,
usually by latching onto a specific receptor
on a certain type of cell,
and they deliver their chemical message.
Hormones help us respond to changes in blood sugar,
prepare our body to flee danger,
tell us when to store or burn extra energy,
they work in concert to prepare bodies
to grow other bodies inside of them,
and as every former teenager knows,
even influence our decision-making and mental state.
(Joe sighs loudly)
Ah, who am I kidding, your brain stays a mess, kids.
You just get better at dealing with it.
But our nervous system is also really good
at passing information to and from distant corners
of our bodies.
Why do we need this extra second layer of communication?
Electrical signals are a great way to communicate quickly.
But often, distant cells and systems
in our bodies need to stay in touch over time.
That gets tricky.
Consider this, controlling puberty
with the nervous system alone,
that would mean nerves firing around the clock
for five or six years.
And more than just signaling long-term changes,
hormones are a way for different parts of our body
to stay in sync and maintain stability.
Imagine different parts of your body getting sleepy
at different times, you'd be a mess.
But luckily, the release of melatonin is produced
by a central gland so it affects the daily rhythms
of every cell in your body simultaneously.
Electrical signals can't do that, but the nervous
and endocrine systems aren't totally separated.
They work in feedback loops.
The endocrine system acts on neurons in the brain,
which controls glands in the brain,
which sends signals to other glands
to tell them to make more or less hormone.
Stress hormones like cortisol can also alter brain function,
even our ability to learn.
And increased levels of sex hormones can make animals act
like complete idiots.
Communicating over large distances over time is a problem
all multicellular life has had to solve,
and it's an incredibly old one.
We find secreted chemical messengers
in everything from single-celled organisms,
to plants, to you, and your dog.
What's weird is that unrelated organisms separated
by enormous distances on the tree of life share
many of the same hormones.
They've just evolved to sometimes use
the same messenger chemical in vastly different ways.
In human bodies, for example,
the hormone, prolactin, is involved with breast growth
and milk production,
but elsewhere in the animal kingdom,
it impacts everything from salt concentrations in fish
to the way that bird bodies get ready to sit on their eggs.
Hormones from one species
can even elicit responses in others.
Back in the 50s, the way we found out
if women were pregnant was by injecting their pee
into frogs or rabbits
and then watching to see
if human hormones kicked off ovulation.
All of this tells us that hormones
and their chemical building blocks are an ancient
and shared way that living things send and receive signals,
maybe as old as complex life itself.
So if you're looking to blame someone
for all those awkward puberty years,
tell it to the slime molds.
So many secretions, stay curious.
And I wanna take a minute to tell you
about our Patreon page.
We rely on the support from our audience,
people like yourself, to help us make videos like this
and do bigger, better, and exciting things.
If you'd like to learn how you can support this show,
you can check the link down in the description.
We've recently reorganized a bunch of our support levels
with new perks, including the opportunity
to submit a dad joke and have it read by me,
a connoisseur of fatherly humor,
a joke like this one perhaps.
What hormone does a fish make when it's in an aquarium?
Indoor fins, swimming inside.
You can submit a better one.
Just visit the link down in the description,
and we'll see you on the next video.
Yo, what's up?
(Joe clucks loudly)
I don't know why I did that.