- [Voiceover] You already discussed
about extracellular receptors a little bit,
how to use a protein in the plasma membrane.
Well, this is showing how that purple oval here,
which is the protein, is embedded in the plasma membrane,
but all it has is a place where the receptor can bind.
That receptor, that little site there,
just is waiting for a signal.
The signal is gonna tell it to perform an action.
In this case, it's time to form the action
to change the substrate into the product.
Well the term substrate is referring to any particle
or any substance that is gonna be used in a reaction.
The product is the end result of a reaction.
So without anything even leaving or entering the cell,
this receptor that receives a signal
on the outside of the cell
can trigger a reaction on the inside of the cell.
So let's get into a little more detail here.
The sodium-potassium pump.
This pump is probably one of the most important pumps
in your body.
It's going to help expel unwanted ions
but keep the ones you need.
It helps keep the cell volume where it should be
to make sure the cell is the proper size, proper shape.
It helps with overall functionality.
This sodium-potassium pump is gonna utilize ATP,
the energy source,
and it will expel three sodium ions
for every two potassium ions it brings in the cell.
So each cycle will take three sodium ions
from inside the cell and push them out.
And then it'll take two potassium ions
from the outside and bring them in.
So let's go through a step by step
to kinda show what that was again.
First off, sodium ions are going into the pump.
If you notice, they're coming from the inside of the cell.
Then you apply some ATP, give it some energy.
When you break that bond, you release the energy.
That purple spheric structure there, that protein,
will then change shape and allow the sodium ions
to be moved to the outside of the cell.
Once it's open to the external environment,
or the outside environment,
you'll then pick up two potassium ions.
K+ is potassium.
Those then will go through, again, a change,
leading to them being released into the cell.
This is necessary because typically
potassium has a high concentration inside.
And that high concentration slowly leaks out.
But sodium has a high concentration on the outside
and that slowly leaks in.
So because these are slowly going down
the concentration gradients,
high concentration sodium outside,
gotta keep pushing back out there
and keep that concentration.
High potassium concentration inside.
It'll keep pulling the potassium in
to keep it as high concentration.
So this is very important to keep the proper volume
of your cell.
These sodium-potassium pump.
So a study states in normal, every day equilibrium,
no problem.
The amount of potassium going out
and the amount of potassium coming in are the same amount.
Amount of sodium going out,
the amount of sodium going in, same amount.
But now when the rate of outward sodium transport
is faster than the inward,
all of a sudden, the cell is shrinking.
But if the sodium transport going out
is less than the sodium coming in,
now the cell is ballooning up, expanding.
The reason being water follows sodium.
Well, where do we find sodium in our bodies?
And the environment around us?
Sodium is part of table salt.
Table salt is NaCL,
so sodium is part of table salt.
This more salt you take in,
a lot of times, the thirstier it gets.
Think about if you ever went to a ball game
and ordered those big, soft pretzels,
the ones loaded with salt.
After you're done eating that, what do you feel?
More often than not, you feel thirsty.
Your body's trying to take in more water
to balance out or reach equilibrium with the sodium.
This movement in and out of fluid from the cell,
controlling the fluid volume, is referred to as tonicity.
Now tonicity itself is the concentration of solutes
in two different fluids.
As far as the cell goes,
we can look at the fluid outside the cell
and the fluid inside the cell.
So your tonicity is comparing these two different fluids.
If you have an isotonic solution,
the fluid inside, intracellular,
and the fluid outside, extracellular,
both have equal ionic concentrations.
You may have heard of the term isotope before,
if you ever had a stay in the hospital.
You're in the hospital with an IV fluid bag, a saline bag.
That is an isotonic solution.
It's meant to help replace fluid in your body
with the same exact ionic concentrations.
So isotonic.
Nothing's really changing much.
They're both equal amounts.
Now in hypertonic,
the extracellular, the fluid outside,
has a high ionic concentration than what's inside.
So hyper means high.
So the extracellular,
the fluid outside has a higher ionic concentration.
Because the outside fluid, or the extracellular fluid,
has a higher concentration, water diffuses out.
The water will leave the cell
and go out of the cell to try and dilute
that extracellular higher ionic concentration.
So the water flows out.
As it leaves the cell,
the cell will start to shrink and shrivel.
If it shrinks and shrivels from enough water loss,
it could potentially die.
But the flip side is hypotonic.
Hypo means low or below.
So now the extracellular ionic concentration
is lower than the intracellular.
So the fluid outside the cell has less ions
than the fluid inside the cell.
Because the internal concentration of ionic ions is higher,
water goes into the cell to try
and diffuse the higher concentration.
The whole idea with both of these
is water is going towards the higher concentration.
Try and dilute it.
So in this hypotonic solution,
as the water goes into the cell,
it'll cause the cell to swell up, get larger.
If enough fluid forces its way into the cell,
it could actually cause the cell to rupture or break open.
Obviously, breaking open the cell will kill it.
So hypertonic, hypotonic.
Both deal with tonicity.
Hypertonic, the outside fluid has a higher concentration.
Hypotonic, the inside fluid has a higher concentration.
Let's look at this diagram.
This is symbolic of red blood cells in a fluid.
The one on the far left,
where you see it has isotonic at the top,
the red blood cell is put in there.
Inside and outside the red blood cell are the same solution.
Nothing happens.
But in the case of a hypertonic solution,
well hypertonic, the outside environment
has a higher solute that causes the cell to shrivel up.
And the last one, the far right, hypotonic.
Well hypotonic means the inside of the cell
has a higher concentration
because the outside around the cell
has a lower, hypo, lower concentration.
So what happens here?
Water flows into the cell,
causing the cell to swell up, get larger.