Hi. It's Mr. Andersen and in this podcast we're going to be talking about
osmoregulation. Before we get into osmoregulation we should define what osmosis is. Remember
that is diffusion of water across a semi-permeable membrane. So let's say right here we have
this U-tube and on this side we have a high molarity of water. So a lot of sugar on this
side. On this side we don't have as much. And so basically the sugar would love to spread
out. But it can't because the sugar can't fit through the semi-permeable membrane. But
the water can. So the water is going to flow from an area of high water concentration to
low water concentration. And so basically if you were to watch this, you couldn't see
the sugar but the water on this side would mysteriously raise. And lower on this side.
It would require no energy. If you were to do the opposite of that, so if you were to
do reverse osmosis, we'd have to squeeze it in this direction. We could get pure water
and that's how you actually purify water if you look on your water bottle. It'll say reverse
osmosis a lot of the time. So how does this impact cells? Because in plant cells it's
okay for there to be movement of water because they have a cell wall. But for us not so much.
And so basically if you were to take a red blood cell and have it sit in an isotonic
environment. In other words an environment where the concentration in the blood and outside
the blood is the same, you're going to get a movement of water but the blood cells are
going to be happy like they're pictured right here.
\b \b0 If you put them in a hypertonic area,
so if you put them in sugary water then water is going to flow out. And you can see that
the red blood cells are going to shrivel up. Likewise if you were to put them in distilled
water, water is going to flow in and they're going to pop. Or they're going to lyse. And
so it's really important to the cells in our body that they remain isotonic. So, what are
the two life strategies? Well the two life strategies are some organisms have just decided
this is too much effort. And so what they are called is osmoconformers. And so an osmoconformer
like this octopus right here, the osmolarity, and so osmolarity remember is going to be
the concentration of solutes to water, is going to be the same on the outside as it
is on the inside. In other words they're just going to be the same osmolarity as their surroundings.
It's nice because they don't have to regulate that. The bad thing is that you're going to
get big swings that can effect the rest of the organism. So a lot of organisms are what
are called osmoregulators. Great example of this would be the brine shrimp that are found
in salt water. Brine shrimp, we would have some like in the Great Salt Lake, basically
what they do is they have to regulate the amount of water inside them. So they live
in a salt water environment. So think about where the water is going to flow. Is it going
to want to flow into them or out of them? That's right. It's going to flow out of them.
So they're going to, water is constantly going to be lost. So they're going to have to do
a lot of effort. In fact 30 percent of their metabolism just goes to regulating this balance
of osmolarity. If we think about fish, or fish that live in a fresh water environment
versus a salt water environment, if you really understand osmosis, this is easy to think
about. If you're a fish living in a fresh water environment, where is the saltier area?
It's going to be inside the fish. And so basically they're going to keep having water flow into
them. And so they don't drink water. That's the blue here. Basically they eat food but
they have urine that is really, really dilute. And that's just because they're going to have
a net influx of water due to osmosis. If you move to a salt water fish, so in a salt water
fish we're going to have the opposite problem now. Now the salt water is going to have a
higher solute concentration. So we're going to have water that's going to keep flowing
out of them. And so they have to actually drink salt water. And their urine is going
to be really really concentrated. Okay. So we're not fish. We're not brine shrimp. We
live on land. And so how do we osmoregulate? Well we osmoregulate using this organ right
here. It's called the kidney. And so this is the kidney. It's going to empty urine into
the bladder. And then we finally get rid of that. But we use that on land to regulate
our osmolarity. And living on land it's almost more important that we're able to do that.
Now this gets a little complex, but if you can hold with me I think you'll understand
how this works. So basically, let me go back for just a second. If this is the kidney right
here. On the inside of the kidney, over and over and over again we're going to have this
which is called the nephron. So the nephron repeated over and over and over essentially
makes a kidney. And so basically what happens is blood is going to flow in. Blood is going
to flow into something called the glomerulus. And then it's going to flow into this which
is called the Bowman's capsule. The Bowman's capsule is going to do one thing. It's going
to filter the blood. We also have proximal and distal tubules. That's important for secretion
and reabsorption. But we're not going to talk about any of that right now. Again what we're
focusing on is the water. Okay. So basically what happens is the blood flows in and a lot
of the water and solutes are going to squirt out and they're going to move into this filtrate.
This is eventually going to become urine. So again this is eventually going to go over
here and end up in your bladder. So basically what's happening down here? Well as it enters
into the renal medulla, basically what's going to happen is water is going to flow out. And
water is going to flow out. And as water starts to flow out the osmolarity inside this descending
tubule is going to increase. And so the concentration at the beginning is around 300 milliosmoles.
But it's going to increase to the point down here where it's around 1200. So we're going
to set up a gradient. And so on this side water is going to flow out. Water is going
to flow out. Water is going to flow out. Now it's not just flowing out into the interstitial
fluid. A lot of that water is being reclaimed because we're going to have capillaries outside
here as well. And so on this descending side of the loop of Henle, that's what this is
called, basically what's going to happen is it's going to release water. And so we're
going to set up a gradient. Now on the ascending side, on the other side, we're . . . on the
right side of it, it's not going to be permeable to water. But it is going to be permeable
to salt. And so basically what's going to happen on this side is we're going to lose
salt. And we're going to lose salt. And we're going to lose salt. And as we get into this
thick portion of the loop of Henle, we're actually pumping that salt out. And so basically
now what we have is a gradient where down here it's 1200 milliosmoles. But then we have
it going all the way back up. So it's 300 milliosmoles up here. And so basically it
goes horizontal all the way across here. So what's the work of all the loop of Henle for?
All of the work is to set up this gradient. And this is called a counter current exchange.
So it's important that the fluid is following an opposite direction. So these are interacting
with each other. So basically we've set up a gradient where on this side it's not as
concentrated. As we move down here it's really really concentrated at the bottom. So let
me remove all of that. So again we're going to have 300 up here. We're going to have 1200
down here. And so basically there's a gradient that goes across like this. Okay. So what
is this? This is called the collecting duct. And so basically now we have control over
that water. And so again this is the filtrate. It's eventually going to become urine. But
basically we can control whether or not we let water out. And we do that using a hormone.
And that hormone is called antidiuertic hormone. Think about the name. It's anti-diuretic.
Diuretic is anything that, just think about diarrhea, it's releasing water. So an antidiuretic
is something that has us hold on to water. So basically we have this gradient right here.
And if we release antidiuretic hormone which is going to come from the posterior pituitary,
it's going to interact on this collecting duct over here. When it interacts with this
collecting duct it basically says you can let water through. And so if you can let water
through, water is going to flow out of here and it's going to flow back into our capillaries
and into our interstitial fluid. And so basically if we secrete a lot of ADH, basically this
gradient is going to allow us to reclaim water. And more water. And more water. And more water.
And more water. And even though we've gotten almost all of the water out of our urine,
it's really concentrated out here. So osmosis is going to pull that water out it. Likewise,
let's say we drank a bunch of water and we don't need to reclaim that. Then we're going
to decrease the amount of ADH. And basically now we can't let water out through here. And
so that water instead is just going to flow out into our urine. And so when you look at
your urine and look at the different color in it, what's responsible for that? Well basically
it's the amount of ADH that we're releasing. But more importantly it's this wonderful gradient
that was set up in the loop of Henle. And so that's osmolarity. Again we're osmoregulators.
And you can thank our kidneys and our nephrons for that. And I hope that's helpful.